Diffraction in Digital Infrared Photography

[@robshea]

Here is the written version with links to all of the test images in the video. blog.robsheaphotography.com/2020/09/15/diffraction-in-infrared-photography.html

[@danyeager7561]

Rob Shea, I can't tell you how pleased I am to have found you! Long-time IR enthusiast (4 converted Canon bodies) who has had his struggles with diffraction, and also likes to run comparisons and tests on the gear; this is WAY beyond my best efforts. Please carry on! Dan

[@robshea]

Thanks so much. I appreciate your feedback!

[@cmolina31]

Thank you for this deep dive into diffraction in IR. I've been fascinated with IR photography for years and I've never seen or heard a clearer explanation on the subject.

[@haroldchester904]

As a newcomer to IR photography, I now know why grass (in particular) looks like mush in my images.

[@williamcurwen7428]

Although an experienced photographer, I am relatively new to infrared, and your very interesting video has explained to me many puzzling anomalies that I have encountered. Thank you for taking the time and making the effort. 👍

[@my-infrareds]

I knew the problem, but I didn´t know the reasons that causes it. Very well explained, I learned a lot. Thankk you very much!

[@pixelstorm1272]

Best IR YT channel on earth!

[@Darriebp]

Thanks so much for sharing your video it gave a much better understanding . i kept thinking i was doing something wrong but i'm learning. You gave me a better insight to this ball game .

[@SidneyPratt]

Thanks Rob, you explained it so even I could understand.

[@shupingyin8082]

You explained this beautifully

[@charlesshearer3591]

An absolute goldmine of information - clealy explained. I am delighted to have found and subscribed to your channel, inspired to get out and about as soon as Covid lockdown regulations ease. many thanks to you for sharing your knowledge and expertise.

[@MikeHarveyPhoto]

Thanks again for your help never thought of this and now it makes sense 👍

[@kbqvist]

A good point that is rarely mentioned

[@rubensakowsky5108]

Thank you kindly, this is incredibly useful.

[@evasabzacami]

Great video 👍🏼

[@BackFocus11]

Wow Rob!! I’m impressed. Great explanation.

[@stephanpaier9887]

That is really superinteresting, it seems, you really live for infrared🤣 Thank you for your work!!!

[@robshea]

My wife thinks so as well, but probably not in a good way. 😜

[@TomReplogle]

Excellent video, thanks!

[@BklynBorn81]

Two things: 1. I love your videos. You make videos that answer so many questions. 2. I have a full spectrum camera with many infrared photos but when I add ND filters, a lot of color is lost. Is there a way to get colorful IR long exposures in-camera?

[@robshea]

Thanks! Kolari Vision makes ND filters that are designed to work in IR. I have been shooting with a couple of them and plan to do a video covering them in the future.

[@BklynBorn81]

@@robshea I will be on the look out for it

[@AddictedtoProjects]

Hi Rob, just like many others, I've only just found this video and I am super happy that you created it for us!! 👏 I specifically searched Google for "how does Infrared influence depth of field" and your result came up right at the top! 😊 I've searched for this, because I have a Full Spectrum, Full Frame Sony A7R (42mpx). I shoot mostly in 590nm and above, using clip filters in the camera body. I noticed that lenses behave WILDLY differently from the visible spectrum. And it's a complete lotery. Most notably, my newer Sigma (14-24) and Tamron (28-200) lenses perform the best, and my older 70's and 90's lenses, which are PIN SHARP in the visible spectrum, perform quite badly in IR. I was also wondering whether the longer wavelengths of IR give you greater depth of field? I 'think' I noticed that in my pictures, but I haven't done any tests to compare to the visible spectrum. So I can't be sure. Do you have any views on that, or is it just a bad assumption? Thank you!!

[@robshea]

Thanks for your feedback! I too am curious about DOF. I picked up a focus calibration chart, that will allow me to test DOF with various filters. Just a few days ago, I shot another series of diffraction test shots using that focus calibration chart, with a different sensor this time. I want to confirm the results of the tests I did for this video with a different sensor. After that, I'd like to do a DOF test with various filters and see if I can measure a difference.

[@AddictedtoProjects]

@@robshea Thanks a million for your lightning fast reply Rob! :) I've got a trip to the English South coast planned for tomorrow, cause we'll get some sun. I know, yay! I have both the Sony A7R (Full Spectrum converted) and a Sony A7R3. I'll run some side-by-side tests tomorrow, using the same lenses and apertures, in the same location/conditions. Let's see whether my theory has legs or not. I'll report back! 🤞

[@AddictedtoProjects]

@@robshea Hi Rob, I took a couple more photos yesterday (minus the promised sun tho.... 😒) and I had some more time to chew on my theory. It doesn't hold water unfortunately. Whilst I 'thought' that IR increases depth of field, I reached the conclusion that the evidence doesn't back it up. I think I confused DoF and 'clarity'. Let me explain: I 've noticed that in certain cases (not always), IR is able to cut through haze and provide more 'clarity' in the picture. I.e. you can see further, and more clearly what is far away in the scene. It's not always present tho... 🤔 I also haven't run enough tests to determine whether this is limited to certain frequencies. Need to run some tests around that. Anyways. If you're interested in a few overcast IR pix taken at the English Jurassic Coast in 590nm, here's my gallery. www.flickr.com/photos/63103097@N04/albums/72157720165559347 Thank you again for sharing your advice and experience with the world! :)

[@robshea]

@@AddictedtoProjects Thanks for sharing your images! I suspect that DOF will be the same or slightly less in IR. I'm looking forward to testing!

[@stevechan5985]

Hi Rob, I received your book yesterday and the chapter on “Diffraction” brought me to this video. For your Fuji XT-2 test you state that the sensors pixel pitch is 3.9 microns. In your 590nm test of the text images you show that f5.6 and f8 are the sharpest apertures. Your table has 590nm Airy disk sizes of 8.1 microns for f5.6 and 11.5 microns for f8 which greatly exceeding the 3.9 micron sensor pixel pitch. I’m confused as why we aren’t seeing the limiting effects of diffraction at those apertures. Using the formula in the video I calculate that f2.5 with an Airy disk size of 3.6 microns would be the sharpest aperture excluding other compounding factors. What am I missing? I’m enjoying your book. Well done.

[@stevechan5985]

I meant to say confounding factors

[@robshea]

Those calculations are for a *specific* wavelength of light. With an infrared high-pass filter of 590 nm, you capture light with wavelengths of around 590 nm *and higher* . The higher you go, the more diffraction there will be. Since we don't typically shoot a single wavelength of light but a range of wavelengths, the complexity of the math increases. Also, this does not account for demosaicing, the impact of which varies depending on the camera. While I find the formulas interesting in understanding the cause of the issue, testing is a more reliable way to see and prepare for the impact of diffraction. This is why I took a simpler approach in the book, compared to the video.

[@stevechan5985]

@@robshea Thank you.

[@Night6436]

Best place for IR. Thanks for your time and sharing your knowledge. Couple of questions tho. I set my white balance in camera. Once in processing, do I need to do it again using the software? And I,m really enjoying IR but what software would you recommend apart from Adobe. I’m not willing to pay for a subscription but I’m willing to pay for a full program. Thanks again for all your efforts.

[@robshea]

If you white balance in camera, then you do not need to white balance when editing. If you shoot in RAW, you have the option of setting WB in-camera, during the edit, or both. I prefer to set the WB during the edit, as this means 1 less setting to worry about when shooting and I find that it gives me the most creative freedom during the edit. If you have a particular consistent style, then setting the WB in-camera is perfectly fine. Check out this video on WB tips: kzbin.info/www/bejne/h4apmqeahZyopcU I have reviews on many different editors and how well these work with infrared. Here is the Infrared Editors playlist: kzbin.info/aero/PLW4H_E25cS0pHBhGYkXte3SAZL9Q9EmgF I will summarize them in the future video. In short, I would recommend darktable for its excellent rendering and it's free, and ON1 for its ease of use and low one-time cost.

[@Night6436]

@@robshea Thanks for your advice.

[@stephanpaier9887]

One question though: does the wavelength (the other way round) also improve the depth of sharpness, so smaller F-stops can be used? Having all those testshots already made it would be interesting to make a spin-off-video and compare the same F-stops with the different wavelengths side by side and compare rhe sharpness of those.... (Pleeeeease......) Best regards, Stephan

[@robshea]

Excellent point! Based on the test images, it does not appear that longer wavelengths increase the depth of field. I suspect that the "sharp zone" between the impact on DOF and the impact of diffraction is just squeezed down with IR. If you view the images in the written summary, you can do these comparisons. blog.robsheaphotography.com/2020/09/15/diffraction-in-infrared-photography.html I added an image test summary that details the sharpest f-stops for each wavelength. You can certainly see the trend there. (590nm doesn't follow the trend, but that may require a re-test.)

[@luismartins3262]

This may not pertain to IR specifically but... Back in the days of reading magazines (Pop Photo, Modern Photo, Petersen's Photo, etc.) usually the sharpest f-stop in a lens was one to two f-stops from wide open. Now in the digital age it seems a shift happened and most lenses are sharpest at the mid range of f-stops. So in those days the aperture sweet spot was about f4 to 5.6, but now the sweet spot is usually f8 to f11. What am I missing here?

[@robshea]

I would still say that the absolute sharpest f-stop on a lens is still 1 to 2-stops from wide open. If you watch Christopher Frost's lens reviews, that's the impression that I get. But with the quality of lenses getting better and better overall, the difference in sharpness between f/4 and f/11 is probably negligible. The bigger factor with a modern lens becomes how much depth of field you want. f/11 will get you more depth of field than f/4, which is certainly desirable for landscapes. That's where you need to be aware of diffraction, for either visible light or infrared. (Of course, this all varies with sensor size.)

[@Lemmispeak]

lol im using a Holga lens which is F8 on my Sony Camera and my gawwd the diffraction is mega :D

[@robshea]

😆 I just picked up a pinhole lens with a fixed f/6.3 and I'm eager to see what the diffraction is like. 🤓

[@Lemmispeak]

@@robshea oof yes link me the results would be interested to see them :)

[@GETTY-gr7gf]

Does INFRA-RED work at night.

[@robshea]

Here are some examples of infrared at night. instagram.com/p/CgCbTdFu-x2/ instagram.com/p/CpaOB_KuV6g/ instagram.com/p/Ch2dYVGu3l6/ instagram.com/p/Cb21vpyupqT/