How To: Build Your Own Schlieren Setup

[@JoshTheEngineer]

Can't get access to a nice mirror? Or you want to try something different? Check out my video on Background Oriented Schlieren (BOS): kzbin.info/www/bejne/jHS4f2hvrZV_fJY

[@aether222]

What kind of cameras can this work with though? Do I need something fancy, or could I use a phone? if not, then how fancy does one need to get?

[@JoshTheEngineer]

@@aether222 You can use your phone without a problem. I would highly recommend putting it on a tripod though. You can get rid of vibrations (as I show in that video), but it's much better if you use a tripod.

[@aether222]

@@JoshTheEngineer What did you think of my idea of using computer methods to further enhance optical Schlieren photography? If computers can enhance regular video to show Schlieren so well, surely some method could enhance optical schlieren to make a super sensitive system?! (even if it needs a version that works with brightness or colour not translation).

[@SeanLavery]

Great tutorial. Thanks for writing out such comprehensive details. Your explanation of how it works gets the point across better than any other professional schlieren mirror video I've seen. I think I am going to try this out myself.

[@JoshTheEngineer]

Thanks, I appreciate it! There are a lot of other nice videos on KZbin showing peoples' setups and results (some mentioned in the video description), but I didn't find any that laid out step-by-step how to make a setup at home, so I thought it would help others who wanted to do it themselves. If you get stuck, feel free to ask me questions.

[@Disktoaster]

Holy smokes dude. I had the 2¢ version of how Schlieren imaging worked before I searched the term and found your video, and by the 1:38 mark you've made it clear the whole trick is the same interaction between point source light and atmosphere that makes stars "twinkle," and described how to recreate it consistently over a variable distance. That's the whole answer to how to build one, but I'mma still watch the rest of the whole video out of respect and expect to learn a hell of a lot more. (Edit: mild dysgraphic moment)

[@elenosandoval778]

Thanks for making this video. I saw the Schlieren effect in a pilot training film describing how moving air causes lift in an aircraft wing. That was in 1967, and I never forgot it. I also never saw it again until I stumbled onto your video. Thanks again!

[@negarbp1306]

thanks for this wonderful video and your comprehensive explanation. we are going to try it!

[@JoshTheEngineer]

Good luck!

[@lore10010]

Thanks a lot for your video! I am from Colombia and probably I wouldn't do it without this explanation!

[@JoshTheEngineer]

Glad I could help!

[@KrzysiuNet]

Thanks, Josh! I thought it's just a good video, but when I saw that mirror stand made from cardboard and adhesive tape, I instantly clicked on "subscribe". DIY in its purest form. Love it!

[@JoshTheEngineer]

You're welcome! Sometimes you just have to use what you have lying around.

[@nicolasscheggia5017]

Thanks for this great video. I've been trying to make a schlieren effect set up for quite some time now, but I thought it would require expensive instruments and tools. After seeing this video I made a quick try with a commercial mirror and I guess it will be possible to make it work.

[@skunkjobb]

Very nice! For years, I have thought about this kind of imaging and not known how they are made and finally I know and would even be able to do it myself if I like to. Many thanks!

[@JoshTheEngineer]

You're welcome! It seems like a lot of other people in the comments have had success with their own setups, so you should definitely try it yourself!

[@jasonmcintosh2632]

This was great! I finally know how to make one of these. Now I just got to find a good reason to make one...

[@alwinian]

Thanks for putting this together. I'm sure it was a lot of work - but for us the viewer. Totally Awesome! Thanks

[@JoshTheEngineer]

I enjoyed doing it, and I'm glad it was helpful!

[@sleepydog4]

Wow, great video! Thank you for the detailed explanation. I was going to do some experiments with a less-then-opticaly accurate parabolic mirror and you saved me from a lot of wasted time.

[@JoshTheEngineer]

Thank you! I'm glad I could help. As you saw at the end of the video, the bathroom mirror produced pretty poor results, but it did technically work. So it ends up being a trade-off between price and quality. Depending on your application, you could start with something you have lying around, and if it doesn't give you what you want, then a move to a higher optical quality might be a good idea.

[@muhammadmahmoud2054]

Thanks man, I've passed my project because of you.

[@JoshTheEngineer]

Awesome to hear!

[@marcuslow9396]

Fantastic video! Makes me feel like trying out on my own!

[@JoshTheEngineer]

Thanks! This is a great little weekend project, and according to my calendar, there's a weekend coming up.

[@gokturktorun]

Thanks for great video, we are going to use this setup to observe ultrasonic soundwave while acoustic levitation.

[@cIimber314]

Oh, thank you so much. I was trying to make Schlierenfotographie for years and at all the sites were I have been everybody talks about putting the camera at 2f. So it never worked. Your video gave me the clue needed that it must sit on 1f. So obvious. I thought I messed up some other component. Now it works. Do you think that one can observe smaller differences in refractiv index of the fluids with better optics?

[@JoshTheEngineer]

You're welcome! I just want to make clear here though that in this double-pass (single mirror) system, the light source and knife edge are in fact located at 2f. That is, two times the focal length of the spherical concave mirror. A better mirror is the easiest (though probably the most expensive) way to get better images. You can also change sensitivity with the knife edge. It will also depend on the size of your light source and the tightness of the focused spot.

[@coolakin]

learned a lot from this. Really nicely explained. Watching the vibrations of you walking is cool.

[@JoshTheEngineer]

Thanks! Yea, the vibrations show just how sensitive the positioning is. I was actually trying to walk carefully/quietly, but I clearly failed.

[@natanaelportillo2401]

That's a cool set up! I like that you used a commercial one to show the difference in quality of the image. It made realize i didnt have to get fancy just experiment with this type of photography. It would be a cool experiment to do in a middle school or high school physics class too, for the teachers out there teaching kids about STEM. Next time you do this, you can try using the spot meter on your camera, your camera will only ready a specific point instead of an area. If you put your nikon on aperature priority, set it to the smallest f/22, with a spot meter (exposure settings (AE, scroll using the wheel, find spot)), you wont have to fiddle around with the exposure compensation as much, or might be able to go darker to get. more contrast which seems key to this type of imaging. Closing your windows would've helped to, your camera wont try to read the ambient light, it would just over expose the experiment. Thank you for taking the time to make this really in depth video! i am taking a compressible flow class and saw this technique being used for past experiments, did some google searches and found some neat videos, yours by far the best! I am a photographer and engineer so this experiment tickled my fancy haha. Good work!! =D

[@JoshTheEngineer]

Thanks! Yea, this setup is super simple and would make a great display for some STEM outreach. That's been on my list of things to do for a science fair or something, now I just need to find the time. Good advice regarding the camera settings. I always just default on matrix metering because that's what I mostly use when I'm outside shooting. Unfortunately the blinds on my windows are what they are, and let quite a bit of light in even when they're fully closed (although after looking at my video again, I noticed I didn't even close them). I'll try the small aperture and spot metering next time I set it up. Thanks for the info! Good luck in your compressible flow class. It was one of my favorites when I took it in undergrad. I actually have quite a few compressible flow videos on my channel if you ever get stuck.

[@jandeturck9967]

Thanks for this great video. I was just trying to quickly find out what Schlieren imaging was, but ended up watching to the end !

[@JoshTheEngineer]

You're welcome! And thanks for sticking it out to the end; I know it's a long video.

[@waynebreivogel1742]

Kudos... well done. A question: if you wanted to capture a sneeze or breath, let’s say an area a little bigger than a head, that would require a mirror of maybe say 12-15 inches. Obviously a quality scientific mirror would get pricey... any suggestion for an “adequate” solution? Perhaps a solar capture plastic mirror? Obviously not “fine”, but perhaps better than the cosmetic mirror. Again, this is a well done demonstration. I showed it my son in law, his response was two simple words... “mind blown”.😉

[@JoshTheEngineer]

Thanks! Yes, mirrors can get quite expensive, especially nice ones that you need for schlieren measurements. One method that doesn't need a mirror is called background oriented schlieren (BOS). I recently made a video going through an entire DIY setup that might interest you (kzbin.info/www/bejne/jHS4f2hvrZV_fJY). You might have some trouble getting it to be as sensitive as a conventional schlieren setup, but this recent video by LaVision shows how sensitive it can be (kzbin.info/www/bejne/oYqtp4huZql-nc0&feature=emb_title). Note that LaVision is a company dedicated to flow diagnostics/visualization/imaging, so what they show is going to be hard to achieve at home with a simplified setup, but you can get pretty close.

[@MyRadDesign]

Cool video. To show the turbulence caused by the heat of the candle it is better to have the candle several centimeters below the center of the mirror. The column of rising air above the candle is laminar for a few centimeters then transitions to turbulent flow. The turbulent flow is more interesting to watch.

[@JoshTheEngineer]

Thanks. You're correct, I could have moved the mirror up a little. However, showing the laminar part is a good way to show how the knife-edge affects the results you're seeing. I didn't switch the knife-edge in this video, but it would have been a good explanation to rotate it 90 degrees, and show that you don't see any gradients.

[@adi13th]

Thank you! I will build a set and put the final result on my tranparent paper paravant which seperates my private space from my working space. Customers will see the result but not the setup. THANK YOU!

[@JoshTheEngineer]

Sounds pretty cool! Good luck!

[@maximivanov8467]

This is a great video, thanks a lot! I'll try to make a similar setup for teaching optics (and convection) at the local polytechnic museum.

[@JoshTheEngineer]

You're welcome! That sounds like a great idea...good luck, and let me know if you run into any problems.

[@Wormsandconditions]

Amazing video. I have a quick question, if you have the time. What is the minimum temperature difference that can be shown in this setup? Can heat rising from a human body be shown like this? Thanks very much.

[@cptechno]

I recently discovered Schlieren imaging. I want to build one myself. There are a few variations that I suggest to you should be investigate. VARIATION #1 You used a vertical position of the razor blade. How different the image would be if the blade was horizontal? Comparing both images vertical/horizontal razor blade position would be interesting. Along the same line, how about puting the razor blade a different angular increments and compare the resulting images? For example, you can choose the angular positions of 0, 15, 30, 45, 60, 75, 90, angular degrees. VARIATION #2 This is something I saw from another KZbin video. They used colored light filters instead razor blade. This gives a far better result because the image is no longer blocked off, but colored. the resulting image gives far more visual information. Another similar variation is to use use two colored filters side-by-side in place of the razor blade. This seems to give the best result of all because the surface of the gradient becomes visible at both poles of the gradient. Another similar variation would be to find a color filter that changes from one color to another. This may be from one color to full transparency. This type of color filter might be harder to find, but they would hold good results because no information about the image would be lost for contrast. VARIATION #3 Use a polar light filter instead of the razor blade. You can use the polar light filter in the cheap 3D glasses given in movie theaters when they show 3D projection movies. Polar filters have a direction up/down or left/right. You can experiment with that in the same way as with the razor blade. First you try one filter replacing the razor blade and see what the result is. The filter might block off too much light and acting like a razon blade. Then you can try two polar filters side-by-side with one having vertical polar direction and the other having horizontal direction. I imaging that the light intensity might have to be increased significantly.

[@svenayu9589]

Incredible video! Every step is so well explained :) Subscribed right away!

[@JoshTheEngineer]

Thank you!

[@rigan47]

Great work Josh! I have a question tho... why is it better to use a spherical mirror instead of a parabolic one? Since parabolic mirror focus collimated light without introducing spherical aberration I fail to understand why shperical mirror is the best choice. Cheers

[@JoshTheEngineer]

Thanks! The spherical mirror is needed for the double-pass schlieren system, whereas the parabolic is needed for the Z-type schlieren system. The one I show in this video is the double-pass, and only requires one mirror. I'll probably make a video on the Z-type system at some point, but it requires two mirrors. You're right that the parabolic mirror collimates the beam, but we actually don't want any collimation for the double-pass method. The spherical mirror is used because if you locate you point source twice the focal distance from the mirror, it will reflect off the spherical mirror and focus back down at the same 2f distance, which is then where we place the knife-edge. For the Z-type system, you place the point source at the focal length of the parabolic mirror, which then collimates the beam, and then a second parabolic mirror takes that collimated beam and focuses it down at one focal length, which is where we place the knife-edge. There are pros and cons to both types of systems, but that's the reasoning for the different mirrors.

[@cynthiacarlisle8534]

Is it possible to see inaudible frequencies that are being broadcast into a house? I am seeking a way to trace their origin. I would really appreciate any information or advice you could give me. Thank you for your video. Very well done!

[@JoshTheEngineer]

Thank you! The sensitivity is realistically going to be too low to see those sound waves, but there are certain instances where you can see them, for instance when you set up a standing wave. There are some demonstrations of schlieren being used for sound wave visualization that you can take a look at (by the Harvard Natural Sciences Lecture Demonstrations).

[@unwindedcom]

awesome!! love that you used stuff that you can almost get anywhere

[@JoshTheEngineer]

Thanks! The goal was to make it easy for anyone to set up at home.

[@yiyou6529]

Thank you for your post! This is the best video I have ever seen about Schlieren-Shadow imaging. I successfully built a mini one with a concave mirror that has a f=50 mm. Most of the parts of mine were 3d printed. I can see hot air, butane and helium. But argon, not really. The mirror I used was a scientific grade concave mirror with aluminum sputtered for UV. Also I used green LED instead of a white one due to the fact that refraction of light is positively related to wave length. I think a blue one might work better. One quick question, have you thought about build one with 2 concave mirrors? That should give you "True" Schlieren imaging and better sensitivity. BTW, I don't think the focal distance is the major factor that determines the sensitivity or image quality. Instead, I think the quality of the pin-hole and the razor blade are the keys. Please correct me if I am wrong about it. Thanks again for you post!

[@JoshTheEngineer]

Thanks for watching; sounds like you have a pretty cool little setup! I definitely want to make a 2-mirror Schlieren setup at some point, but the reason for making this one is that it is the cheapest for the frugal DIY-er. It's also pretty easy to construct and align everything. I'll probably get around to make a more scientific setup at some point. There are a lot of different aspects of the system that affect the sensitivity. I mentioned the mirror as (arguably) the most important component because of the uniformity of light that we see in the images. If the mirror is poorly constructed, you'll get some dark spots, and the light source won't focus back to a perfect point. This then makes the razor blade placement a little tricky. I do think that the focal length is important for sensitivity because if you think of the divergence of the ray from it's nominal (non-refracted) path, the longer the focal length is, the farther the displacement from its final location it will be when it gets to the 2f distance. This makes it more sensitive to pick up lower density gradients. However, like you mention, knife-edge placement is also key. You can pick up different gradient directions by aligning the knife-edge vertically, horizontally, etc. You can also block all the undisturbed light as well by making sure the knife-edge covers the center of the beam, and then you'll only see the refracted light. There are a lot of different opportunities with regard to the knife-edge design and placement that will affect what you see in the image or video. So it really ends up being a combination of many components that influences the sensitivity and images you see, and it's hard for me to confidently say that this one component matters more than that one without getting into some more advanced optics equations.

[@johnnyjohnson2894]

Great info, looking forward to trying this out. Cheers!

[@umeshm1518]

Hey Josh, Thanks for the video. I have a question by the way. I saw your reply to one of the comments below, where you mentioned that the first step in Schlieren is getting a uniformly lit mirror. What exactly needs to be done to achieve this? I am using an 8" dia, 30" focal length mirror with a Nikon D610 for visualization. I can visualize the flow patterns, but my mirror is not uniformly lit and the image is just focussed on a small portion of the mirror. What should I do to get it over the whole mirror?

[@JoshTheEngineer]

No problem! The easiest way to get a uniformly lit mirror is to take out the knife-edge completely, and place your camera (behind the point where the light focuses back down to a point) in a location where you see the mirror completely filled. You've probably tried this already, so here are two more things to check. First, make sure your light source is diverging enough such that it completely fills the mirror. As an extreme example, if you use a laser point without a diverging lens, the light spot you'll see in your camera will only be as big as the laser beam diameter. You can see in my Laser Schlieren video (kzbin.info/www/bejne/gKeri4eVrKeji6c) that when I use a diverging lens, the light overfills my mirror a little bit, which is better than it under-filling the mirror. Second, make sure your aperture (F-stop) is open as wide as it can go (lower numbers). I was trying to take some high speed Schlieren a little while ago, and it turns out I couldn't attach my lens of choice to the camera because it would auto-adjust the F-stop to the smallest aperture (highest number). I had to use a manual-aperture lens with that body so that I could make sure the lens was wide open, which didn't restrict the light entering the camera. Try checking this, and let me know if it doesn't solve the problem.

[@simonsantama]

Great video! interesting, very well done and easy to understand.

[@JoshTheEngineer]

I'm glad you liked it! Thanks for the positive feedback.

[@ABitOfTheUniverse]

Expect a lot more views and comments now that brusspup has released a video on this. A lot of people are going to want to know how it works and how he set things up and this is one of the best explanations, if not the best, of the setup. Thanks for sharing this with us.

[@Doct0r0710]

Yep. I come from that video too. Didn't know that you can do that in your own home

[@JoshTheEngineer]

My pleasure. I made this video so that anyone would be able to make the setup in their own home, and it looks like it has helped a few people!

[@lordchickenhawk]

I also came here from Brusspup because I wanted to understand why it works. Thanks for the explanation, it was clear and concise. Now that I have seen what the Schlieren effect does, I realise that I have been seeing photos of such in books since childhood (40+ years ago now!) Until now I never realised that those images were made in a concave mirror... inspite of the fact that said photos were always round instead of rectangular. Thanks Josh!

[@JoshTheEngineer]

That's what I'm here for! And yep, you'll see Schlieren images in almost every engineering book that deals with fluids or aerodynamics. It's a great way to visualize stuff that you normally can't see.

[@Doct0r0710]

Btw I tried it last Friday, and it worked great. For the mirror I used the mirror from a Newtonian telescope. That's big enough, and very smooth.

[@yuesu4458]

Hi thank you for this great video! If I don't want to buy a camera, can I use my iPhone camera instead?

[@JoshTheEngineer]

Thanks! And yes, absolutely. Back when made this video I had taken some images with my Samsung phone and it worked just fine. You'll have more control with a dedicated camera, but you'll absolutely be able to get nice images/videos with your phone.

[@youssefdirani]

+JoshTheEngineer do you think it will work if 1 foot behind the razor blade we placed a white paper as a screen so we get the image? I mean not to use a camera

[@JoshTheEngineer]

That should also work, since the camera is mainly there so you can record images or videos. You might also notice that if you take the razor blade out of the setup, you can place a piece of paper where your camera would generally be, and you should still be able to see something that looks like Schlieren, but is actually called shadowgraph.

[@youssefdirani]

shadowgram yes

[@morancium]

Awesome sir .....its truly Amazing ........i am gonna try today !!! thanks a lot !!

[@JoshTheEngineer]

Glad I could help. Good luck!

[@minettesumaoang6814]

Hi. We're trying to make a Schlieren set up for our research. And we want to use a 50 cm Diameter mirror. We'll be making our own mirror using space blankets. Is it possible that we can still get images???

[@JoshTheEngineer]

I think you'll definitely get something, though I'm not sure what kind of quality it will be. I had wanted to try this setup with the mirrors that NightHawkInLight made, so let me know how they work!

[@molnarmilan8350]

Fantastic experiment! It is possible to se the effect with eye without camera? Thank you!

[@JoshTheEngineer]

Yep! You can just take out the camera and hold up a piece of paper a little farther back behind where the camera was. The farther you move the paper back, the larger the image gets, but it will also get dimmer. However, you'll be able to see the effect no problem. Note that the image will be upside down. You can also switch between Schlieren and shadowgraph by pulling out the knife edge.

[@Lee-he2gf]

Hello! I was wondering if why we need a small light source. What happens if we use a larger light source? Thx for your video, it helped me a lot in understanding Schlieren photography.

[@lemongames268]

the result wont be as focused, so you'd get smaller quality of shclieren effect

[@ahmadalias7271]

Hi Josh, just a quick question. How different is this set-up compared to the "Z" system Schlieren? Which set-up is actually better (more sensitive and representative) to capture the observed phenomena

[@JoshTheEngineer]

There are a few differences, but the main one is that the Z-type is a single-pass, while the setup I have is a double-pass. That is, in my setup, the light first passes through the object (heat from the flame), hits the mirror, then comes back through the object again. It also means that the light is diverging and converging as it passes through the object. For the Z-type, you collimate the light on the first mirror, then the collimated light passes through the object (not diverging or converging because it's collimated), and then it is focused back down to the knife-edge/camera with another mirror. So for my setup you only need one mirror, while for the Z-type you'll need two. I believe the setup I used is the cheapest and easiest to set up for the layman, but I think most researchers use the Z-type (or something more complex).

[@workshopscience425]

Hi Josh and Ahmad, As Josh said, a Z type arrangement is found more commonly in research labs. This is for a few benefits of practicality a double-pass system doesn't allow: For critical image making (& quantitative analysis), micro adjustments need to be made in every component of the system. With the light source for example, often the LED (or other point source) is spread out to create a source which isn't quite considered "point". The benefit of this is that the system is no longer an "on"/"off" phenomena, but some of the normal rays are allowed to pass, and this gives different data in the image with a more embossed feel. This is why laser doesn't often make a great source. With a Z system, parabolic mirrors rather than spherical mirrors are used. This way the collimated light can be better calibrated without any astigmatism. Each of the mirrors are also on a micro-adjustment mount (which is often more expensive than the mirrors). Aside from the adjustments a Z system gives, it also allows for quick conversion to a great shadowgraph setup, or allows for different variations of schlieren - color cutoff, color direction indicating and so on. Often the image needs to be resized at the camera position, so that the entire mirror can fill the field of view of the sensor - this is done via various options in optics, but a simple achromat doublet is best. Having said this, a z arrangement is not necessarily best. Spherical mirrors are more readily available in bigger sizes (think old telescope mirrors), and if you really want to go big, you can use a grid schlieren system. I have also often come across lens schlieren systems, however these are typically riddled with distracting artefacts from the lenses themselves. Fine for data collection though. I hope this helps

[@JoshTheEngineer]

Thanks for your more detailed response!

[@ahmadalias7271]

Thanks guys for the assistance. I have developed the "Z-type" Schlieren system using two parabolic mirrors and seems to have captured something.

[@gabrielacosta7196]

Josh, can I use this setup for large images, like the air moving around people's bodies as they walk? If yes, I should change the scale of what objects?

[@JoshTheEngineer]

Yes, it's possible to do this. With this particular setup, you'd essentially just need a larger diameter mirror. There are other methods/setups that might be better for larger subjects though. One that I'd like to try in the future is Background Oriented Schlieren.

[@gabrielacosta7196]

Thanks Josh!

[@JoshTheEngineer]

You're welcome!

[@muhammadfarooqi]

amazzzzzzzzzzzzzing.. and really loved it.. I would try to buy some good quality mirror.. but did you try this with even more easy using MOBILE's Camera with manual focus or something?

[@JoshTheEngineer]

Yea, I tried it with both an old digital camera and my phone's camera. Both worked, but the quality was obviously lower than using my DSLR.

[@allenwegner]

im sure you probably know XD but all radioshacks are closed now, is there anywhere else you suggest getting the LED and if so what specs LED did you use??

[@JoshTheEngineer]

Yea, unfortunately they were starting to go out of business when I made this video. If I were you I would just buy a pack of LEDs off of Amazon. You can get a bunch of them for pretty cheap. I just used the standard 5 mm clear LED, but you can honestly use whatever kind you want.

[@victoryfirst2878]

Hello Josh, I have a stupid question for you concerning night vision cameras ??? Since the camera uses infrared light to enhance the light around the lens this can easily be seen with an app on a smartphone. This defeats the purpose of in cognito of the camera in the first place. What can I do to be able to film what is going on to about 400 feet distance with good resolution ??? Is there something you can be kind enough to guide me in the right direction if there is something out there in the field with a reasonable price ???? Thanks a bunch and peace. Your video is very well done with the right ratio of information and whiteboard illustrations. Thanks a bunch and peace too.

[@samanthaknepp7049]

Great video! I am curious, how important is the camera quality?

[@rileynorkett8714]

I have been trying to get this to work for a few days now. I am using a DSLR camera, a concave mirror with a 24" focal length and a razor blade setup just as yours is in this video. I am getting to a point where the mirror appears gray-ish, like in this video. However when I turn any heat source on in front of the mirror, nothing shows up in the image. Any tips? I have tried a couple different light sources including an LED flashlight with the reflector taken out and a black cover over the top with a hole in it and an LED point source like yours in the video.

[@JoshTheEngineer]

I'm assuming you've pretty much set up everything the way I do it in the video, so let's work through a couple scenarios and see if that helps. If you remove the knife edge completely from your system (and you don't put anything in the beam path, which I'll just call a candle from now on for simplicity), you should get a uniform light distribution on your mirror as viewed through your camera. If you do, that's a good first step. The next thing to do is to place the knife-edge in the beam path, at the point where the beam focuses down to a point, still without the candle. If you cover up half the beam with the knife-edge (you'll see half the beam spot on the knife-edge, even though it'll be small), then you should see your intensity go down, but it will still be uniform. The more you move your knife-edge into the beam, the dimmer the image on your camera will get, but it will always stay uniformly lit. After the knife-edge blocks the beam, you obviously won't see any light passing through to your camera. If everything makes sense up to now and is working like I mentioned, then you should bring the knife-edge back to the point where it's covering about half the beam spot at the focus. As we saw before, you'll have a uniformly lit mirror, but it will be dimmer than if there were no knife-edge in. No place your candle as close to the mirror as you can without it burning or heating up the mirror, maybe an inch away. You should see something now on the camera. If you pull the knife-edge out of the beam path slowly, then you'll see the sensitivity decrease, and the mirror will become uniformly lit at the full intensity of the light source. If you move the knife-edge farther into the beam spot, you'll still "see the heat", but the background intensity will go down. If you look at the video that the KZbinr "brusspup" posted, you can see in that setup that he has most of the beam spot covered by the knife-edge, which is why the background looks so dull and gray. I personally don't like the way that looks, so I usually do about 50% coverage, and then adjust back and forth until I get an image I like. A couple of other things to note. Orientation of the knife-edge does matter. If you're looking for horizontal gradients of index of refraction, then you need to orient the knife-edge vertically, as I do in the video. If you are looking for vertical gradients of index of refraction, then you need to orient the knife-edge horizontally. Or you can do it at an angle and be slightly sensitive to both. For a candle, put the knife-edge in vertically because the index of refraction changes abruptly in the horizontal direction. Also make sure that your return beam spot is coming back as close to the LED source as possible (within reason). This will eliminate double images. You might need to adjust your exposure compensation on the camera too, because as you can see in my video when I bring it back to 0 (no compensation), you can't see much on the mirror. Another KZbin comment mentioned that I could have used spot metering as opposed to matrix metering for my exposure, where the spot would be fixed on the mirror such that it was correctly exposed for the mirror light. Hope something in this response helps with your setup! If it does, let me know what fixed it.

[@josewagner8739]

Hey Josh very nice video. I would like to know why we have to put the blade in 2 times the focal distance. Thanks

[@Multiunitaz]

Thanks bro, for this explanation! Hail from Russia!

[@JoshTheEngineer]

You're welcome, and hello!

[@knightriderwindtalkerlv513]

Thanks Josh, awesome video with great explanation. I have a question, would placing the light source and knife edge at the focal point work as well? since at focal point the light will also come back as a dot just similar to 2f point. Also, is the led bulb collimated? Does the light source need to be collimated? Thank you!

[@JoshTheEngineer]

You're welcome! If you placed the light source at the focal point, the light would actually leave the mirrors collimated, and wouldn't focus back down again. This is actually what the Z-type Schlieren system does. You place the light at the focal point, collimate it with a mirror, then use another mirror to focus the collimated light back down to a point at the second mirror's focal point, which is where you would place your knife edge. This way, you get collimated light through your object of interest. The LED is not collimated; it emits light in all directions. You don't want a collimated light source, because it needs to diverge out to fill the mirror. Lasers are collimated, which is why in my other Laser Schlieren video, I use a lens to diverge the light so it encompasses the mirror.

[@PleochroicSpodumene]

Hey there, awesome video that seems very 'complete' in both theory and practical setup. I was wondering if there would be much advantage/disadvantage in using a laser pointer as your light source? I am guessing you need the beam to be divergent enough to cover the mirror but still coming from as small a point as possible. I may have misunderstood something but as you were using the word laser a lot so I wondered if it was because it would be of benefit to use one if you had it?

[@JoshTheEngineer]

Hah, yes I use the word 'laser' a lot because I work with lasers in my research and I'm so used to saying it, so I slipped up a few times in this video! You can definitely use a laser though, and I actually have with my setup. You're correct that you'll need to diverge the beam to cover the mirror. Here's how I did it. I have a simple red laser pointer that you can buy for a couple of bucks. I bought a plano-convex lens to diverge the beam from the laser (search Thorlabs LA1213 on Google, it's the first choice). This happens to diverge the beam just the right amount to cover the mirror in my setup. If it diverges too much, you'll lose intensity, and if it doesn't diverge enough, you won't use all of the usable area of your mirror. I got pretty good results with the laser, but you should note that you'll definitely get a speckle pattern show up in your images. This is just an unavoidable thing that comes with using lasers. I like the pictures I get from my LED better, but if you're using a higher quality or high power laser, it might be better. I say this a lot, but the quality depends on a lot of factors, and it's hard to make sweeping generalizations. You should definitely try it out though, and see for yourself!

[@PhilTaylorPhotog]

HpyCmp3r just a short note about lasers..yes they will work but there a few issues with them. Being a coherent light source, you will struggle to get a very clean field due to the patterns you get, and as they are monochromatic light sources, you will experience greater diffraction around the knife edge. This in turn will make the image a little less sharp. A red laser will be safer here as the wavelengths are far longer. Hope that helps you both.

[@wcsc0829]

if the LED is placed at 2f position and the viewing angle of the LED is too large does that mean not all of the reaches the mirror and being reflected? if thats the case does that mean i need to use the tangent formula and calculate the half angle of the LED to choose the most appropriate one?

[@rajibkudas123]

Urs videos are always so well explained...

[@JoshTheEngineer]

Thank you!

[@rajibkudas123]

Please if U can make a video on implementing vortex panel method in Matlab...For plotting Cp, P for NACA aerofoil

[@yzz234]

WHAT A NICE VIDEO!!!! but,I think in this system the light has passed the Density variation region twice， I think，it will has some infulence for this system。

[@JoshTheEngineer]

Thanks! Yes, in this setup with only one mirror, the light passes through on the way to the mirror, and then again on its way back to the camera. A Z-type system is a little more straightforward in that the light only passes through the region of interest once, but you also need to buy an extra mirror.

[@fzigunov]

I'm amazed!! Great explanation, thanks for sharing!!!

[@JoshTheEngineer]

My pleasure!

[@JoshTheEngineer]

Very cool! I'm glad you got it working! I love seeing results from people using my video as a guide, so thank you for posting this.

[@UrbanoZea]

Does it work if you don't use a point source, but instead use a light source that produces beams parallel to the principal axis of the mirror, and place the blade edge and camera at the exact focal length instead of twice the focal length?

[@JoshTheEngineer]

That's actually sorta what the Z-type Schlieren system does. You're essentially just skipping the first mirror part, which collimates a beam from a point source located at the focal point of a parabolic mirror. Then after the collimated beam passes through the region of interest, another parabolic mirror focuses the light rays down to a focus, where a knife edge is located, and then into your camera.

[@avasangel5559]

In other video's , the light source or "medium" was put right in front of the Mirror, and looked completely different than this way on your video. ?? A bit u clear to me now. Will you help a rookie out?

[@GeeveGeorge]

Who's here from after watching veritasium? Great tutorial Josh , thank you :)

[@JoshTheEngineer]

Yea, Derek had a pretty cool setup going. It also helps having a big mirror! Thanks for watching!

[@sprusedgoose162]

me, I actual got it to work from a cheap mirror

[@RobertShane]

Veritasium just posted a new video on schlieren

[@insightfool]

Very cool detailed instruction. Thank you!

[@JoshTheEngineer]

Glad you liked it!

[@GglSux]

Very interesting, and clearly explained, thanks a lot. Best regards

[@JoshTheEngineer]

No problem!

[@GglSux]

+JoshTheEngineer Excuse a couple of possibly stupid questions, but if One wanted to build/test this Yourself, what are the most important "criteria" to make the "system" "clear", and easy/robust to set up. I wonder mostly what one should "look for" regarding the mirror, as this seems to be the hardest part to get (and most expensive;). Is larger mirror always better than a smaller(qualities otherwise equal), and what about "focal distance", is longer always better than shorter,or vice versa. Or is the "sweet spot" simply only dictated by the "size" You want Your set up to be. ((I mean I understand that the focal distance dictates the "size",what I'm not sure about is whether Your set up was "deliberately chosen" to be that "lenght/size" due to some underlying reason. Or that it simply was due to that "this was the mirror You got") And would it be possible to use a laser as a light source, if so would this have any advantages,or drawbacks ? (EXEPT the obvious that You of course can (should) NOT observe the reflection with a naked eye) (Appologies for the verbose questions) Best regards.

[@JoshTheEngineer]

You have some good questions here. Regarding the most important part of the system, I would say the mirror is the crucial component. As you can see from my setup, there aren't really that many parts involved, and the mirror is the one that has the biggest impact on the quality, as long as you have everything set up correctly. With a nice mirror, you'll get uniform light distribution in your videos/images before you put the knife-edge in place, which can be critical if you want to see minute details in your flow when you do finally put the knife-edge in. What I mean by that is if you look at the end of the video, that bathroom/makeup mirror I use is clearly of poor quality for these types of experiments, and even without the knife-edge in place, the light distribution on the mirror is not even close to being uniform. It makes alignment more difficult too. There's a trade-off regarding the mirrors though, to get to your next question. The three-way trade-off for me is between large mirror diameter, long focal length, and camera zoom. It would usually prefer a larger mirror because the things I can look at can be bigger. However, if you have too large of a mirror and a dimmer light source, then you'll have less light intensity over the surface area of the mirror. It might matter, but it might not, just something to take into account. To increase sensitivity, a longer focal length is better, but at some point, your setup will just be too large, and won't be able to fit in the room. In my other couple of videos I did with a larger mirror, the focal length was pretty long and I had to position my mirror and camera on opposite sides of the room. In this video, you can see that the mirror never takes up the full screen because my camera couldn't zoom in far enough. When I switched to the larger mirror, it still doesn't fill up the whole frame because the focal length of the mirror increased. The main reason I used the mirror I did in this video is because it was a high quality mirror with a long focal length for a very reasonable price. That's pretty much it. I have used a red laser pointer as a light source with a diverging lens attached to the front of it, and it worked pretty great. The main drawback with that laser pointer is the speckle pattern was pretty bad and it was magnified because I diverged the beam to fit on the mirror surface. There will always be a speckle pattern with any laser, but higher quality ones will be better in general. This was just a couple dollar laser pointer I was using. But yes, definitely make sure you don't look straight into the laser!

[@330MillionGods]

Does it give more clear picture because distortion happens, twice, once going towards mirror, once light returning from mirror ?

[@JoshTheEngineer]

The double-pass nature of this particular setup makes it more sensitive to distortions. So it's really the sensitivity that's increased, not necessarily the clarity of the picture/video.

[@joemonster55]

Great demo! Could you now make a DIY supersonic wind tunnel to watch some shock waves?!

[@JoshTheEngineer]

+joemonster55 That sounds like something that I would definitely be interested in doing (i.e, make a shock tube with a little viewport and a place to insert a mini model). However, this will take some more time to think about and execute. I do have some other interesting ideas about how to use this setup to visualize shock waves from bullets, etc. I will probably post a couple more videos describing minor perturbations to this setup first, such as using the external camera flash instead of the LED. But if you have any cool ideas, let me know!

[@rotgertesla]

+JoshTheEngineer I would also be interested in a DIY video of a shocktube to see some shockwave (If the cost can be kept down like we see in this video). Can a simple paintball gun produce a supersonic shockwave if we fire it into low pressure air?

[@JoshTheEngineer]

The shock tube idea is definitely still on my to-do list for the future. I have so many other videos I'm trying to work through at the moment, but I'm going through some calculations for a shock tube design that would result in shocks strong enough to be seen by a simple Schlieren system like I showed in this video. I also wanted to do a video on Schlieren images for some sort of gun or projectile launcher, so that's in the works as well. I would have to look more into paintball gun firing velocities, but I can guarantee that you would see something coming out of the front. What you see and with how much sensitivity will be dependent on the gun characteristics and the sensitivity of the Schlieren setup (focal length, mirror quality, light uniform-ness, and so on).

[@TheTrumanZoo]

you might be able to sell pre prepared sets? nicely fixed lens holders and the correct distances etc :)

[@JoshTheEngineer]

Hah, that would be nice! I've been 3D printing some parts for this setup, so when I get all the kinks out, I'll make those files available.

[@TheTrumanZoo]

that is even more humane, wow im surprised. im like that myself, did not expect that :D i just share it and seed ideas into the world. still, for peoiple without acces to a 3d printer, you could offer a starter kit :d well balanced etc, or a little booklet i dont know :D keep up the awesome work!

[@TheTrumanZoo]

do you often engineer projects etc? im working on a 3D ufo model that i think could work, like a drone only everything doubled in xyz like rotors on top and below working in tandem. im looking for someone with engineering experience for a few pointers perhaps. :0 some one who likes to help save this world :)

[@itwrdoomed6720]

Hello josh, I'm 15 and I from France, in high school we have to do a project in groupe of 2 or 3 about the topic we want and the final mark of this project count for the baccalaureate. So I think that in our project we will do this experience : first we'll put a brick behind a ventilator, then we'll put a little car (a toys) behind the ventilator. thanks to your tuto, we will be able to see what will do the air and we will be able to compare the effect of the ventilator's air on the two objects and the effect of the objects on the ventilator's air. Could you tell me If you think it's a good or a bad idea? I don't know if you managed to understand what I mean so I'm sorry if you don't. Thank you a lot for your video !

[@mikehalloran93]

Cool vid! Is this gonna be the start of a DIY series? Or is it a one hit wonder.

[@JoshTheEngineer]

+mikehalloran93 There will most certainly be more DIY videos; I'm no Natalie Imbruglia. Get it?! You'll get there eventually.

[@__-cd9ug]

Hi! I believe I have everything needed at home. The mirror is one of those that you put in the bathroom I hope it'll work! I'll find a razor blade somewhere in the house and there must be a LED lying around as well. My only problem is that my camera is a semi-DSLR?(if there's such a thing ahah) By that I mean you can't zoom in and out manually and you can't really adjust the exposure. Will it work in a super dark room? I'll try to cover any lights or maybe put a long cardboard box between the camera and the mirror. I don't know, if you have any suggestions please help me! This project looks so cool

[@__-cd9ug]

help me maybe?

[@JoshTheEngineer]

Hello! The mirror I use at the end of the video is a bathroom mirror, so you can see that maybe you won't get the crystal clear images like I get with my good mirror, but you should still be able to get something. If you don't have a razor blade lying around, you can always use a knife, just be careful. You can use any light source, even a light bulb, as long as you put a cover over it and poke a little hole in that cover to make a quasi-point source. I've gotten good results with my DSLR, my point-and-shoot circa 2005, and with my phone. The main problem you'll run into is that you won't be able to zoom in on the mirror, so it might be sort of small on your screen or in you picture you take. That's the problem I have, since I don't have a lens that zooms far enough. Your camera should definitely have some sort of exposure setting. All three cameras I just mentioned have the option to adjust the exposure manually, even my phone. I would just check the manual for the camera. It's easier if the room is dark, but as you can see in my video, I'm taking this video during the day, so that should work just fine too. Good luck!

[@randall642]

What did the razer do? Trying to understand the need for the knife edge. Awesome video Edit: kind of understand now.. The knife edge is just blocking a corner of the light, blocking some rays but letting others pass..

[@JoshTheEngineer]

Sorry for the delayed response; I've had a busy summer. Like you said, the knife edge blocks some of the light from getting to the camera. Based on the angle that the light gets refracted as it passes through the air, it will either get blocked by the knife-edge or it will be allowed to pass by and into the camera.

[@deweyOnce]

Hi Josh, absolutely love the video. I in fact just built a setup in my living room with a 1300mm FL mirror. It is a telescope mirror, and fits this experiment well. I am creating this as part of my physics final project. One question though. I have everything setup, and light a match or something, the image that I am seeing is everything I need to see, but it's inverted. Placing things at the bottom of the mirror is showing at the top of the mirror, and the smoke is going downwards (upwards). Any thoughts as to why?

[@youssefdirani]

+JoshTheEngineer Can we use the camera of a mobile phone? I mean instead of a special camera? Does it usually work?

[@JoshTheEngineer]

Yep, that will work. I used my Samsung phone with this setup too and it worked, I just didn't want to make this video longer than it already was. The video is higher quality with the DSLR, but a phone's camera can definitely work. You'll still need a way to make sure it doesn't move, so I ended up buying a little phone mount that attaches to my tripod (for a few dollars).

[@gustavotorres2899]

i can place the setup further than 2ft? does the light - camera distance matter and how could i calculate it?

[@JoshTheEngineer]

The separation distance between the light source and mirror is dictated by the focal length of your mirror. Your light source needs to be twice the focal length of your mirror away from the mirror. If you don't know the focal length of your mirror, you can find it like I show in the video, using the flashlight on your phone.

[@avinotion]

X2 the focal length of the mirror is the radius of the theoretical sphere the mirror was cut out of. Or R=2f Oh and thanks a bunch for this video!

[@hasnainqaisrani3961]

This video is very good. Do you have any idea to see the flow dynamics inside a tube whose dimension are in mm. Either it should be a circular or square

[@JoshTheEngineer]

Are you interested in building a shock tube? If so, I would recommend going with circular cross-section tubes. If you use square cross-sections, you'll have to worry about stresses at the corners when you pressurize the driver. Circular tubes are better for pressurization. When you say 'dimensions are in mm', do you mean that you're trying to build a very small one? You also need to be concerned with the boundary layer that develops along the length of your tube. If you have a very small diameter tube, you probably won't have a uniform freestream near your test article. Is this what you meant? I might have misinterpreted your question. If I did, try to rephrase it and I'll give it another shot!

[@hasnainqaisrani3961]

I want to see dynamics of fluid inside the tube which is nearly 8 cm long with inner diameter is 4 mm and the tube is square shaped. I can see the flow outside but i cannot see anything inside tube. Do you have any idea or suggestion to solve this problem.

[@JoshTheEngineer]

The tube diameter is quite small, and I think it will be difficult to get optical access to it. You'll have some boundary layer interaction which will make it difficult to understand exactly what is happening in the tube. What flow velocities are you looking at? The first step is to simply put a window looking into the tube. If you don't have optical access, you can't do any sort of Schlieren imaging.

[@chinadedream]

hello, I what to ask you a question. Thanks . Will schlieren work if we are trying to watch the shock wave in the circular pipe. the pipe is glass and 12cm in diameter and 1cm in chickness. actually, I want to now Circular structure will make schileren impossible?

[@JoshTheEngineer]

You'll find that if you put a transparent circular tube in front of the mirror, it will look black on your camera since the light isn't passing through and hitting your sensor. The way most people look at shock tubes with a Schlieren setup is to have a square cross-section with flat windows. A better setup would also be either the two-mirror Z-type setup or a two-lens setup. Both of these collimate the light as it passes through the test section so the windows won't affect the videos or images.

[@chinadedream]

Wow, thank you for your kind answer. Just several days ago, I came up an idea to use a cylindrical lens behind the tube to compensate the cylindrical structural effect and We are make a cylinrical lens now. ^_^

[@heidiwong9035]

May I ask what is the minimum focal length of the concave mirror should be? Cause the mirror with 750 mm sounds a bit expensive for me ha:P Also, are there any requirement for the thickness and wavelength range of the mirror? Thank you!

[@heidiwong9035]

Also, I check from your link on edmund optics, which displayed two mirror, one is with focal length of 75mm and one is with 1500mm. Is the 75mm one is the mirror you bought? Can the setup be worked with the one with 75mm?

[@heidiwong9035]

Sorry for asking too many questions. Thanks!

[@MrWnw]

Can I use a concave mirror that has a holder in the middle? That means there is a black circular spot right in the middle. Will it matter? Please help, Thank you very much!

[@JoshTheEngineer]

You can use the mirror, but you'll just have a black spot in the middle. I'm guessing you have a telescope mirror or something like that? It should work, but just note that you'll only being able to see the light around the center spot. I think there are a few Schlieren videos out there that use the same kind of mirror you have.

[@MrWnw]

Yeah, it's one mirror out of many from huge observatory telescope. One university offered me to borrow it. Unfortunatelly I couldn't get to anything better. We will see what are the reselts gonna be. TY for help, mate!

[@JoshTheEngineer]

No problem. Good luck!

[@MrWnw]

Why do I need LED (point) light source? The regular bulb would do it it too shining everywhere, wouldnt it? The goal is to hit an entire mirror with light, right?

[@arichinweze]

Hello !!! please how do I select a suitable camera for the schlieren system.... I intend capturing spray parameters of a nozzle and the combustion of a fuel.... will Nikon d40 work??

[@JoshTheEngineer]

Yea, that camera should be great for this. I'm using a Nikon D3200 for my videos. I don't have the right lens though, since I need a little more zoom. I'm using my 18-55mm kit lens that came with the camera, but I wanted to use a higher zoom lens so I can fill the screen with the mirror. If you watch my other Schlieren videos, you'll see that even with a bigger mirror, it doesn't help because they focal length had increased so I had to move my camera farther away. Ideally, you would want a high-speed camera and a large enough zoom lens.

[@arichinweze]

JoshTheEngineer Thank you so much for the explanation ...

[@theendisnear9395]

When i attempt to do this set up and test to find the focal point of the mirror using my phone, it ends up being almost directly in front the mirror where that little dot is smallest, is there something that i am doing wrong or is there something wrong with my mirror?

[@JoshTheEngineer]

It sounds like your mirror just has a really short focal length. That was the case for the bathroom mirror that I use at the end of the video (although it still had a long enough focal length to get a decent image). You might want to get a mirror with a focal length more like the one I use in this video.

[@theendisnear9395]

I believe the focal length of my mirror is 75mm is it still possible to do this with such a small length? And also I ordered my mirror from the website in the link Edmund Optics

[@fxsrider]

I have two meade LX telescopes that have nice mirrors but failed electronics. An 8 and a 12 inch. Nice basement to set it up in for the distance. Time to get busy!

[@JoshTheEngineer]

Sounds great! You can also try a Z setup with two mirrors.

[@fxsrider]

Hi Josh, I tried to set up my 8 inch Meade SCT last night. I took the corrector off along with the secondary mirror. They aren't suited for this. The focal point of the primary mirror is 16 inches where it is folded by the secondary into a baffle toward the visual back. The mirror also has a good sized hole to fit the baffle. I had considered it would be a problem way before starting but played with it anyway. Any ideas? I did notice if I place a bright LED flashlight smack in front at 16" I get a focal point across the room on the far wall. Unless I am confused. I thought you were focusing on a pinpoint with your camera. I'm not clear how you could resolve that tiny point into something useful. I'll watch it again.

[@fxsrider]

I figured it out.

[@fxsrider]

I managed some butane. I did not use the blade to block light. Maybe the camera was offset enough. Actually I was almost 2X distant from the light source focal point. kzbin.info/www/bejne/aHO2dpScbqanqNE

[@pitufimota]

hello, I don't get why you need a sharp metal thing, would it be possible to do it using a plastic materials?

[@JoshTheEngineer]

You need something sharp/straight so that it has a well defined edge to cut off the light. You also need it to be thin (axially along the beam path) because if it's too thick, it will get in the way of the beam as it's focusing down to the point. A razor blade just happens to satisfy both of these limitations, and they're inexpensive. You should try it with a different object, and see how that changes your results!

[@usithamihiranga5977]

Thanks for your explanation...❤❤❤

[@JoshTheEngineer]

You're welcome!

[@VinceHradil]

Great detail. Thanks for the video!

[@JoshTheEngineer]

You're welcome!

[@Jjerem5]

Thanks for this vidéo man. It was very helpful.

[@JoshTheEngineer]

You're welcome!

[@utubeaccess7]

Will a parabolic mirror work? I have an 8" in my telescope.

[@JoshTheEngineer]

While the optimal mirror for this double-pass system is a spherical concave mirror, a parabolic mirror will still work okay. For the Z-type (two-mirror) schlieren system, the parabolic mirror is the optimal choice. I'm currently filming a spherical vs. parabolic mirror comparison for schlieren systems where I'll go over why you can use either, but also how performance is degraded depending on which system you're using it in. I'm also editing a Z-type schlieren system video, so if you have two telescope parabolic mirrors, you can get some really nice images from that system.

[@rotgertesla]

Succes! I got clear picture with a small flame thank you

[@JoshTheEngineer]

Awesome! Glad I could help out.

[@laurysa17]

Hi! What is 2F, is the focus? Im a little bit confused to emulate this at the laboratory, the focus is the distance between the midle of the mirror and the radio? Thanks for ur help! Have a nice day!

[@JoshTheEngineer]

The value 'f' is the focal length of the mirror, and the value '2f' is just two times this focal length. At around 6:06 in the video, you can see the website for where I bought my mirror, and the focal length is listed in the column labeled F.L. as 750 mm. The significance of the 2f distance is that if you put a light point-source at 2f away from the mirror, it will focus back down to a point at that same 2f distance. So when you are setting up your system, make sure you put the light source as close to 2f from the mirror as you can. In the video at 12:19, I'm finding the 2f distance by using my phone's flashlight. I keep moving the phone away from the mirror until the spot on my phone case is smallest. This is the 2f distance, and this is where I begin the rest of the setup. I could have also just used a ruler to measure the 2f distance from my mirror using the value given on the website. If you have any other questions, let me know and I'll do my best to help!

[@laurysa17]

Hi! I using a led, maybe the same like you, but my focal point (the little point in the blade) its conical, not a sphere and soooo big!!! I dont know how to do for change that... My schlieren photos have poor quality, my mirror have 150 mm.

[@laurysa17]

Thanks for ur help!!!! :)

[@JoshTheEngineer]

Alright so there's a few things you should check. 1) Make sure your light source (your LED) is as close to a point-source as possible. In my video, I do this by putting the aluminum foil with a little hole cut into it over the LED. The smaller the light source pin-point, the smaller the focused image will be on your blade/knife-edge. You can see in the video how the size of the image changes before an after I put the aluminum foil/black paper on. 2) Make sure your LED point source is 2f away from the mirror, and that the knife-edge/blade is also 2f away from the mirror, sitting directly next to the LED. 3) A couple things about your mirror. You need to make sure you have a concave spherical mirror. If you don't, the LED point-source won't focus back down to a point at 2f away from the mirror. Towards the end of the video I showed that you can get the system to work with a standard bathroom mirror, but the quality is poor. The second thing is that I'm guessing you mean your mirror has a focal length of 150 mm? If that is the case, then the refracted light might not have enough distance to separate from the non-refracted light, and your system won't have much sensitivity. I would try to get a longer focal length mirror if you can.

[@조준형-t4p]

Could you explain why the Schlieren Photography measures the first derivative of the gas density? If say one gas has a density of 1kg/m3 and another type of gas has a density of 1.2kg/m3, would they have the same brightness if you look through each gas?

[@JoshTheEngineer]

I will probably do another quick video explaining why it's the first derivative, but the derivation is a little too long to put into words here. In the meantime, search Google for ' Introduction to Shadowgraph and Schlieren Imaging", and click the first link (it should be a PDF from RIT). I found this document very helpful, and maybe that will answer some of your questions. The derivation can also be found in Elements of Gas Dynamics by Liepmann and Roshko. The book is very good and inexpensive on Amazon. It is primarily a book on compressible flow, but it has a chapter dedicated to experimental methods, and Schlieren is a section in that chapter.

[@대한민국-s6p]

Have you posted a new video explaining why it's the first derivative? If so could you post me a link? Or if you haven't could you reply that you haven't made it? Thanks^^

[@hodron7854]

perfectly explained! gonna try soon

[@JoshTheEngineer]

Awesome, good luck!

[@SRG-Learn]

Woah, really awesome, thanks for sharing your knowledge.

[@JoshTheEngineer]

Happy to help!

[@rdarabosh]

That is Awesome!! I think I'm going to make one!! Thanks

[@JoshTheEngineer]

No problem. Good luck!

[@lariacg]

Thank you so much! Now I understand why and how this effect works. I tried to replicate this in home and it worked. Not perfectly because the mirror was not very accurate.

[@JoshTheEngineer]

Awesome! Even getting it to work a little bit is a big accomplishment!

[@arichinweze]

Thanks so much for the video. Please how do I go about schlieren imaging without a mirror(capturing directly with a camera) , using lenses only......pros and cons if any ..

[@JoshTheEngineer]

You're welcome! I haven't constructed a mirror-less system, so I can't give you any details from personal experience. If you're using a point light source, then you need a lens to collimate that diverging light. The collimated beam will then pass through the region of interest, and you will use another lens to take that collimated beam and focus it down to a point. You can put the knife-edge at the focus point, and then your camera after the knife-edge. That's how I would get started if I were setting this up. Take a look at my laser Schlieren video to see how you can use a lens to focus a collimated beam, and vice versa.

[@clarybelle]

does it have to be 2 feet away or can we bring the camera closer?

[@JoshTheEngineer]

You can play around with where the camera goes after the knife-edge. Its placement isn't as important as the other components, but it should be located such that you get as large of an image on your camera sensor as possible.

[@BarlowFilms]

Thank you for making this video.

[@JoshTheEngineer]

No problem!

[@Vinzmannn]

Why is it 2f? I thought the focal length is the length that everything gets focused down at?

[@ANMOLSHARMA-is5yw]

Hey Josh, firstly thank you for explicating in a way so vivid and secondly i wanted to ask how do we colour the images seen...do we use a filter or a coloured knife edge , please tell in detail.

[@JoshTheEngineer]

There are a couple of options that you could pursue. The first is to use the setup with the knife edge, and then attach a colored filter to the other side of the knife edge where the light is passing by. If you just use a single-color filter, then you'll see the normal Schlieren image, but in color now instead of white. To get this same effect, you could just put a color filter in front of your light source. So if I place a blue filter in either of those locations, I'll get my normal images, but now they'll be tinted blue. That's not very helpful aside from making our original image a different color without post-processing. The second option is to, again, leave the knife-edge in the setup, and attach something like a rainbow filter to the side of the knife-edge where the light is passing by. Let's say we attach the filter such that the red is closest to the blade, and the blue is farthest from the blade. This means that the light that is getting refracted the least (but still passing by the knife-edge) will be colored red, while the light that is refracted the most (but still passing by the knife-edge) will be colored blue. There will still be parts of your image that are dark, where the light was refracted the other way and is being blocked by the knife-edge. This is probably the best method for coloring your images.

[@ANMOLSHARMA-is5yw]

By a filter do we mean a coloured paper?

[@JoshTheEngineer]

Pretty much, yes. It needs to be transparent enough to let light through, but change its color while doing so. I would recommend something like transparencies that you can put on overhead projectors. If you print a color spectrum/gradient on one of those sheets, that would probably work pretty well.

[@ANMOLSHARMA-is5yw]

Thanks a ton!

[@brunolorenzo4574]

Does it also work with a magnifying glass?

[@veronikagaminek757]

Hey great post, thank you. I tried it by my own for my study and I only get a shadow construction. Do you may knnow what I´m doing wrong?

[@JoshTheEngineer]

First, set up the light source, mirror, and the camera, without the knife-edge. If it is set up correctly, you should get a uniform light intensity on your mirror (as seen in the camera's viewfinder). If you place an object in front of the mirror, you should just see the object's shadow. If you don't have uniform light intensity, it could be because your camera is not in the correct location, or because you have a less-than-perfect mirror. When you have made sure that the light distribution is uniform, place the knife edge at the 2f point, and cut off about half of the focused dot of light. If you don't have anything in front of the mirror, you should see the light intensity decrease in your camera, but it will still be uniform on the mirror (i.e. it will still look like the mirror is uniformly lit up, just slightly dimmer than it was before without the knife-edge). At this point I recommend placing a candle in front of the mirror, so that you can leave it there while you adjust the knife-edge. Assuming everything was done as I mentioned in the previous two paragraphs, you should only need to make minor side-to-side (or up-down, depending on what direction you want to see gradients in) adjustments of the knife-edge. If you put the knife-edge in and you can't see any light bouncing off the mirror in your camera's viewfinder, then the knife-edge is blocking too much light. If you put the knife-edge in, along with a candle, and you still only see the uniform light distribution on the mirror, the knife-edge isn't blocking enough of the focused beam spot. Keep adjusting back and forth until you see the gradients. Hope that helps.

[@veronikagaminek757]

+JoshTheEngineer thank you so much for your detailed answer and that you take your time for helping me. I tried it like you explained to me, but i didn´t get a focus point at 2f form my reflected light. The focus point is at f and unfortunatly it didn´t work when I replace the knife edge there. Do i have a wrong mirror? Or is the falt at my light source. I just using a flashlight with a LED inside an put a aluminium foil over it with a small point like you showed in your video. Could this be the Problem? And do you use a normal camera, like for example a sony or so? Or is this a special optic camera? Thaaank you so much for helping :)

[@JoshTheEngineer]

The light source should be fine. I've used all sorts of light sources, from LEDs, to USB lights with a pinhole mask, to the flash from my camera. As long as the light source is very small, that won't be the problem. I'm suspicious of your mirror. Are you sure you're using a spherical concave mirror? It should work with a concave parabolic mirror as well, but the concave spherical is the best. If you put the light source 2f from your mirror, and the light doesn't focus back down to a point at the same 2f distance, then you might not have the correct mirror. For the spherical concave mirror, if you place the point source at the focal distance (f), then it should collimate the light reflecting off the mirror. That is, if you put your light source at the focus of the mirror (not 2f, just f), the reflected light coming of the mirror should be a constant diameter spot of light that is the diameter of the mirror. I use my Nikon D3200 with a 15-55mm lens for two reasons. The first is that I have the most zoom with this lens, up to 55 mm. The second is that I can easily adjust the exposure compensation down to -5.0. I've used my point-and-shoot camera that I've had since around 2005, and I've also used the camera on my phone. You should really be able to use any camera you have lying around, but the DSLR is by far the easiest.

[@production-li3ij]

HI, actually what is the led mask?...i did not see at the details part...

[@JoshTheEngineer]

Yea, I ran out of room in the video description. To create the point-source, I use a little piece of aluminum foil, and poked a hole in it with a pin or a needle. For the black mask, I bought a piece of black construction paper, and cut a little rectangle out that would fit over the circuit board. Then I cut a small circular hole in it so that I could slide it over the LED.

[@MarkStadsklev]

Will a parabolic concave mirror work? 29" DIAMETER ACRYLIC PARABOLIC MIRROR CONCAVE MINOR SCRATCHES Excellent Cond.

[@JoshTheEngineer]

You can do this double-pass with a parabolic concave mirror, but the results are best with a spherical concave mirror. However, if you can get two parabolic mirrors, you can make a Z-type Schlieren setup.

[@sabitkondakc9147]

Do we see refraction pattern which propogated from the sharp razor edge?. Like Newton Rings. Camera handles the rest of the jobs.

[@JoshTheEngineer]

Light will always be diffracted around objects like the razor, but it's not something you'll be able to see or notice in these final images or videos.