Aperture & f-stop Myths Debunked: The Importance of the Entrance Pupil

[@chrissummitt6537]

Good job. I am a photographer and have a PhD in optical engineering so I work with the real f/# equations on a daily basis. I was curious if you'd pull it off and you did. You're correct when you say that not many people get this right, but you did. Keep up the good work.

[@geraldundone]

Thanks, Chris. I'm glad you commented since this is your field. Really happy to hear that I did well. Much appreciated--made my day! 😃💪

[@anglichaninblin]

PhD in optics ? Good lord gracious have mercy 🤦🏻‍♂️

[@NTGNS]

Good for you mate!

[@sansone9651]

Ahahahahha you are super funny Chris !

[@kenmastersmaster]

Can someone explain how a smartphone camera with a 4.23mm lens at f1.5 will give you ABOUT the same look as a camera with a 27mm at f5? Given that the DSLR has a 1 inch or larger sensor, from an optics point of view? Is it all computational photography? How can a tiny lens and sensor achieve amazing pictures these days.

[@dunnadidit]

Holy damn...I'm pretty sure my brain did just get undone. I need a good long nap and then to watch this again.

[@geraldundone]

Haha! Thanks, Dunna! 😃👍

[@BrentODell]

I've watched it three times :)

[@DeadPool-dp8zk]

Thanks

[@JohnSmith-hm8xl]

I lost it somewhere around 14cm diameter, and I can't thing anything til the video end and my aunt calling me

[@marekmucha2300]

That’s exactly what I thought, and I keep in mind that I still have to get to the next video, what the depth of field really is about...

[@mrgoldy7532]

These 2 videos on clearing up aperture and depth of field are the most educational videos on photography

[@dajael]

Man...if you are "mostly" reciting this stuff from memory and NOT reading it while speaking it.....then I give up at life! I mean,...Dude!...not only that but...you just (through ALL that stuff you said) caused some sort of diaphragm to open in my head (ha...you see what I did there) and now I just "Get It"!!! I have always struggled with being able to quickly do the math because the system seemed counterintuitive. You keep killin it Gerald Undone! Thanks for this one!

[@geraldundone]

Thanks a lot! That's really nice. 👍😃 Behind-the-scenes scoop: I'd love to be able to read a script, because that would make the videos so much easier! But I've never found a way of doing it without looking like I'm just reading. So, instead I just have my notes that I want to talk about and then start runnin' my mouth. Sometimes I get tripped up and have to do it over again, hence the cuts, but I'm a lot better at it than I was when I started.

[@shirokuro73]

I'm composing a super complicated formula for calculating how many times I need to click the like button. But first, I need to watch this epic video several more times and take copious notes.

[@PeterMKent]

Great video, I always thought it was the front element but the math never exactly lined up and no one seemed to know any better to correct me. This clears up a long standing question I've had for years, thanks.

[@geraldundone]

Thanks, Peter! I'm glad. Appreciate the comment as usual. 😃👍

[@GoExperimental]

It would take me a good 6 months of research and planning to make a video like this and I still wouldn't do it the same justice. Unreal.

[@Myers_toast78]

100% agree 😅

[@Ram.Saketh]

A super thanks as I found this video super helpful! As always your videos are technically sound and a pleasure to watch and learn from.

[@stephenscharf6293]

Finally! A YT video that actually explains the _science_ behind the f/#. Good job, Gerald!

[@grappler185]

I love this guy's approach to teaching!!! If I'm ever looking for info on anything camera or videography related, I search for "[topic] Gerald Undone". This video is 5 years old. He's only getting better!

[@sdk4073]

This stuff is so good, I barely trust any other youtubers now.

[@mick2d2]

Great educational video, I bet not a lot of people know this. This is what makes KZbin so interesting to explore.

[@eguitarstar]

Did I just attend college again? Thanks very much for this, I still got a lot to learn.

[@marvinbeatz6266]

Love this channel cause you go deep and dont just talk about what is usually talked about

[@geraldundone]

Thanks! I'm glad you're enjoying it. Cheers!

[@markgriffin65]

Late to the party but I'm a photographer twenty years and I'm watching this going...ah ha.. lol, fair play. It's a great video and super helpful...you learn something new everyday, thanks man.

[@pebmets]

Excellent video. You have a great way of explaining the technical information that makes it easy for someone to understand without having to dumb it down.

[@MustafaAlNuaimi]

Good thing it's morning here so I can catch up😉 Another example is the beefy vintage lenses (I think it's called soligor 180mm 1.8) have a smooth bokeh similar to 1.4 or 1.2

[@cmitchellfly]

It IS "nitpicky", which is why I'm watching. Excellent, thank you!

[@kevinsim1514]

Thank you, Gerald, for enlightening! Wow! This is the brainiest photography channel on youtube and I’m totally loving it. I’m one of the said beginners you imagine are watching this. I’mma have to re-watch it a few more times to wrap my head around this. Good job! 👍🏽👏🏽

[@geraldundone]

Thanks, Kevin! That's very kind. Glad you like the channel. Cheers!

[@OSidat]

Great "undoing" of a very common misconception, Gerald. Thumbs Up!!

[@TubeThings]

Holy!!! I’m so glad this channel exists! Love stuff like this!

[@Joel4JC]

All I can say is WOW! The truth will set you free! Great Video, please, please keep them coming!! I just love watching your videos!

[@liamtain]

I just came across this video... It’s my new favorite thing. THIS video caused me to subscribe. I appreciate a lot of the content of yours I see. But this is pure gold. Thank you.

[@geraldundone]

Thanks so much! I'm glad you decided to subscribe. Cheers!

[@jonathanlogan6953]

I appreciate the nerdy details in this video. Thanks for sharing!

[@JohnBaxendale]

Totally the best description of this I've *ever* seen, thank you, brilliant videos!

[@jessicapaige9979]

Exactly the information I was looking for. Extremely informative, literally A LOT of information I produce commercials for advertising, and have to tell the talent this all the time. Slow down. It was difficult to digest the words because it was too much too fast. I played it at .75 speed and that was closer to normal speaking. A speed of .8 or .85 would have been better. Its the most common mistake everyone who gets in front of a camera makes. Especially people who know their material inside and out.

[@bonsaimediahousetx]

I clicked this video saying to myself, "harrumph harrumph... I know this information, let's see if Gerald is on target." Then Gerald told me what I thought to be true - because I was profoundly incorrect it seems, and also explained the origin story of my incorrectness, and got me all undone. Luckily I feel put back together and content like the end of a 70's sitcom. Good stuff Geraldo.

[@geraldundone]

Haha. Quite the journey you went on. 😜👍

[@adamn3917]

Unbelievable. Probably best video ive ever seen. Well done.

[@geraldundone]

Wow! Huge compliment. Thank you very much! 😃🙏

[@st.michaelthearchangel7774]

I definitely did not understand all of that, but good to know this information exists regarding the truth of this misconception. Thanks for making this video!

[@yancy1109]

Thank you very much. This explanation totally solved my doubt about aperture.

[@GlenAndFriendsCooking]

That's why all my lenses are T-stops.

[@geraldundone]

Indeed! 😃

[@timbeaton5045]

Yes, a further video on T-stops and why they are not the same as F-Stops would be great. And why they are more suited to film making, rather than still photography. I have watched a couple of videos on this, and still don't quite get it! Keep up the great work with your technical explanation videos, as well as gear videos. We can alway use more knowledge!

[@GlenAndFriendsCooking]

Hey @Gerald... I’m in the GTA (Ajax) with a pile of cine T stop lenses, if you want to come out and shoot something.

[@geraldundone]

Thanks for the offer! Nice to know another KZbinr from not too far away. Also, interesting channel you've got there. 😃

[@GlenAndFriendsCooking]

Thanks - Anytime!

[@philfyphil]

OMG, where the hell was KZbin in the 70s! Some people don't appreciate what they have in this day and age. Subscribed God damn it, subscribed!

[@Photographicelements]

I love videos like this! & who said you will never use math after high school? This is a much needed video; so many opioners just repeat what they heard & pass it off as facts. This video is simple to understand; (and will be shared). (warning: if you are considering a video in the difference between f-stops & t-stops, it is one of the most heated debates the comment section; not sure if that’s the “engagement” you want).

[@geraldundone]

Thanks a lot! Great comment... as usual. 😃👍 Thanks for the heads up on the t-stop vs f-stop debate. I'll tread carefully if I tackle that one.

Wow dude! As a newby photographer, this kind of video is super instructive and well done. Animated graphics really help understanding. Thanks for doing it. I only watched 2 videos from your channel (both are explanations) and love it. I just subscribed. Have a nice day!

[@geraldundone]

Thanks! That's so great to hear. I'm glad the videos are helpful and am happy to have a new subscriber. Cheers! 😃👍

[@scottmilholland176]

Thanks for these videos brother. I watched them in backwards order (depth of field first) but helpful either way. I will definitely be sharing these with some friends of mine. I'm very impressed with all of your videos I've seen so far and you definitely earned a sub from me! Thanks for the great, thoughtful content.

[@joe.mccord]

Amazing channel Gerald and yes, Glen and Tim pointed out exactly what I was thinking. A video on T-Stops would be awesome! I love my set of Rokinon Cine DS and can't imagine shooting without them unless I was doing something else besides narrative. Thanks again for all your knowledge, sir!

[@geraldundone]

Thanks a lot, Joe! Actually, since publishing this video, I've made a video on T-stops: kzbin.info/www/bejne/eGPXnJ2ZpLpoa7s I hope you like it! 😃👍

[@zargle5924]

Oh my lord finally it’s starting to make sense. Thank you for this video. It may be nit picky but as you said these specifics matter.

[@gkochanowsky]

That's interesting. Most of what I know about lenses is based on simple single or doublet lenses taken as one or two lens systems. Modern photography lenses are much more complicated things and I was unfamiliar with how the lens characteristics of simple lenses translated to photo lenses. Thanks for the introduction.

[@6rimR3ap3r]

That finally explains zoom lenses with constant maximum aperture to me. Thank you!

[@geraldundone]

Awesome! I'm glad I could help. Cheers & thanks for the comment. 😃👍

[@MiaogisTeas]

Thanks! That next video is gonna be great, can't wait!

[@hopejides]

your video has the very high quality of amination！ every clip is perfect editing and design， i really enjoyed ！ thanks for your time make those for all audience！

[@geraldundone]

Thanks, Jeff! I appreciate you noticing the details.

[@robertnelson3179]

Wow that cleared up the issues I have had thanks for the video

[@musicmarketing]

you are the man, Gerald! thanks for all the learnins - adding you to our featured channels

[@geraldundone]

Thank you very much!

[@rondelr7626]

Excellent description as always!

[@musicxsam1]

alright! enough youtube for today. i need to nap on this and watch it like 3-4 times to get all this! i dont know how to thank you enough @Gerald Undone 🙌🏻

[@stankmt5016]

Can't wait for the depth of field video

[@visitwithus]

This is the best explanation I have EVER heard on this subject. Now, I understand it all (I think). Thank you, from a noob. Love your channel. :) Oh, and BTW, your opening 'theme tune' is the ultimate ear worm - can't stop bloody humming it.

[@geraldundone]

Thank you very very much! Huge compliment and it means a lot. And also, haha, I'm glad it got stuck in your head. Cheers! 😃🙏

[@visitwithus]

Yes, the conversation in our house is something like this - wife:“what are You CONSTANTLY muttering?” me:”erm, you wouldn’t understand.” 😬😂

[@geraldundone]

😂😃💜

[@JeremiahStringer]

I’m here from Camera Conspiracy! Great stuff man

[@YashMenghani]

Amazing explanation of the concept, this was really helpful.

[@JericTamayo]

So much to learn about the equations and calculations lol. Thanks again Gerald!

[@antontserepanov9720]

I have started getting into lenses a bit more than a month ago (because kit lens required upgrade :D) and of course, I was looking into faster lenses. And having an engineering background, I was really wondering why nobody mentions entrance pupil size, it kinda makes sense that bigger entrance hole lets more light inside. So in my mind, it was that f-stop is telling only which part of the light that enters the pupil can go to the sensor. But still, need to do more research on that topic, yet this video is an excellent starting point. Thank you!

[@aamsergie]

You know when you have a great book on your shelf, one that you always revisit because every time you read it you pick up something new. This video is that book.

[@hunterd8020]

Love this! Could you make a video about different film stock sizes and aspect ratios? I've seen a lot of conflicting information on full frame, super 35, 16mm, etc and I know you would get everything straightened out. Keep up the great work!

[@alesimaboudi8567]

Indepreneur sent me! Keep up all the amazing work!

[@OneHarp]

Excellent! Please keep these videos coming! I love learning the real mechanics of what happens inside my lenses and cameras, rather than the same old "received wisdom,"which often "works" but is technically wrong.

[@geraldundone]

Awesome! I will. Thanks for the comment--that's exactly the response I was going for. Cheers! 😃

[@goldog2816]

Great videos Gerald much appreciated .........

[@jumopellicano]

Dude, you re great! Salutations from Brazil!

[@ForestCinema]

Best explanation ever.

[@manio143]

Can't wait for the next video! It all starts to make sense now :) Also, you have a pretty great community watching your videos judging by the comments.

[@geraldundone]

Thanks! I agree, the comments have been great. Awesome group of viewers!

[@khuo0219]

I tried to explain f stops and sensor size and focal lengths to my wife the other day and I totally failed. Then I realized that I just don't understand the mechanics enough to teach them to another person. Let me watch this 3 more times to see if I can do it next time.

[@aebonstudio7193]

Better than film school!

[@geraldundone]

Thanks, mate! Cheers. 😃

[@madjoints]

this is nerd talk, and my friend...you nailed it!

[@satyam_279]

Best explaination ever 👍

[@keithbennett5179]

Made my photo brain hurt.... is this the crazy part? Good video sir!

[@certoglenn4840]

You aced another one, Gerald. Today's blue ribbon award. The fastest lens I ever had was a Rokinon 28mm, f2.8 fixed lens. That was proven the day I left it on the back, right fender of my Buick and pulled away from the curb somewhere in the Appalachian Mountains. I've no idea the speed it went down the side of the mountain. It's true; it's true. 1989, I think.

[@geraldundone]

Hahaha. Thanks! 😂👍

[@GravityKnightFlying]

Dood. Your videos are so damn good. For people who actually want to know how this stuff really works.... and not just look at specs on a piece of paper. Well... done.. Mr..... Undone!

[@geraldundone]

Thank you very much! Appreciate that.

[@Dustinrhoades]

Both helpful and entertaining!

[@allancollins9565]

thanks mate great explanation keep up the great work Please explain the difference between an Fstop lens and a Tstop lens in one of your upcoming videos.

[@stefansmuts8882]

Awesome video! Please make more like this!

[@geraldundone]

Will do! Thanks for the comment. Cheers. 😃👍

[@HybridphotoPro]

All good Gerald, great job!

[@SSingh-nr8qz]

This is awesome but god my head hurts. Math has never been my friend. The explanation is one of the best I have seen.

[@DetailixFilms]

Very Nice Explanations here!. These nerdy videos are the go to source on YT if you really want in-depth knowledge on that Stuff!

[@ifell3]

Wow really well described!! Surprised you have not got more likes and subs!!

[@geraldundone]

Thanks a lot! Appreciate it.

[@55whiplash]

I love this geek out, we salute you.

[@storybart]

Super intersting and clear explanation! No need to shout at us though, we're just here to learn 😋

[@MurrayFrost]

Sweet! I don't have to go to film school! I'll just watch these! :D

[@winterkat8693]

I was thinking the same thing Gerald concluded to a few days ago.. kept my brain from sleeping all night long lolz

[@BrentODell]

Ok, I'm ready for the next part :)

[@geraldundone]

Haha. Thanks! Gimme a couple days. 😃👍

[@JaeRobinson]

First visit to your channel .. Holy Cow! Super glad to have stopped by .. [subscribed - rang the 'bell'] .. and so looking forward to becoming more "undone" .. Thanks!

[@geraldundone]

Thanks, Jae! Appreciate the comment and the sub. Look forward to having you around. 😃👍

[@rajlovinglife]

this is great ...nicely put but i need to go back and play it more to understand......with good clarity.....

[@speedbird737]

blimey - glad I didn't ask about the number of mega pixels ;-) seriously though a brilliant explanation

[@SteveMayedaTV]

You’re a genius man. Can you do a video breaking down focal length. Like I get that a 50mm lens is a 50mm focal length but what is actually 50mm? Do that have to do with the curvature of the lens? Great stuff man

[@geraldundone]

Thanks, Steve! And thanks for the video idea. 😃

[@geraldundone]

Hey, Steve! I've responded to your question in the latest video. Check it out if you've got time: kzbin.info/www/bejne/Z5PdeaFomLCqgqs 😃

[@chewen771]

Very informative, thanks!

[@geraldundone]

😃👍

[@bottomendbliss]

Epox sent me hear. Dig your vids. Just the kind of info im after. Subscribed.

[@tysonator5433]

I need to go back to school and study photography......I thought I knew it all,..ha lol Great video again Gerald..

[@geraldundone]

Thanks, Tyson! Cheers.

[@mitchellpayton9800]

Dude: it's like half your videos are things I already know, half of them are things I *thought* I knew but was wrong about, and half of them are about things I couldn't care less about (like math). But seriously, this video is amazing -- but like half yer videos (plus or minus 49%) I'm gonna have to bookmark this thing and watch it periodically until it all just sorta "sinks in" like that "moment of clarity" Jules talks about in "Pulp Fiction" Thanks again.

[@tedk2814]

absolutely great channel but I only get one out of every for or five words, wish I could play it back at 3/4 speed. Probably just me but there is little chance I can digest most of your teaching at that pace. no matter though, I really want to get a solid understanding so I'll just play & pause. thanks much,

[@JOEBLACK1979]

Thanks for sharing bro!

[@4lanesmanagement291]

This is a dope channel recommend to us by indepreneur

[@PhotoArtBrussels]

Great video, well explained. As you got into this ... can you shed some light on the mumbo-jumbo of sensor size an f-stop? Is a f2.8 on M43 the same as f2.8 on full frame? Not taking into account potential depth of field changes, etc.

[@geraldundone]

Sure! So they are the same in terms of exposure. Meaning the image will look as bright, but m4/3 has more gain, because it's a smaller sensor, so it will be noisier than full frame. It's four times noisier. And like you said, there is also twice the depth of field. So the true equivalent for DoF and noise would be something like (MFT = f/2.8 & ISO 400) is (FF = f/5.6 & ISO 1600) In terms of the math however, you figure out the diameter the same, an f/2.8 is still an f/2.8 whether it's full frame or m43. Hope that makes sense.

[@jensdanbolt6953]

For that, I would first watch his previous video titled "Cropped lenses on cropped bodies". From that and other sources, here is what I got: Yes, it is the same. The f-number is a physical measurement of the aperture compared to focal length and (as he explained in this video) the magnification, and gives the same light intensity. So with equal ISO, shutter speed and f-number, you will get the exact same exposure (brightness) regardless of sensor size. However; 1) With a smaller sensor you will get more noise. 2) If you use the same focal length you will get a tighter shot (but same depth of field!) 3) If you step back until you get the same field of view, the subject is not as close to the camera and thus you get less background blur. Using the aperture, there is however a way around this to get the exact same noise, depth of field and field of view. Let's use APS-C vs. Full Frame as the example: You take a picture with the full frame camera using a 90mm lens at f3.0 and 400 ISO. With your APS-C camera, use a 60mm lens and set the aperture to f2.0 and you will have both equivalent field of view and depth of field to the 90mm f3. However, you are at f2 which is about one stop brighter than f3, so turn the ISO down to 200 (one stop down from 400) to get the same exposure, and you will also have the same amount of noise. So in essence, if you start to think of equivalence, you must do so with all the settings to get the exact same result: ISO, Aperture and focal length. However if you are not thinking about trying to emulate another sensor size, you can ignore that and know that 50mm is 50mm, and f2.8 is f2.8 regardless of what lens sits behind it. They are physical dimensions, and if you know your camera you know what they will do to your photos.

[@geraldundone]

Looks like @Jens Danbolt and I were working on the answer at the same time. And I'm happy to know we have given similar info. 😃

[@PhotoArtBrussels]

I already have! ;-) Thanks for the tip!!

[@MiaogisTeas]

@@jensdanbolt6953 Not attacking you it's a great explanation, but I don't understand why someone would give a rat's donkey about equivalency - if people would just go and learn what their tools can and can't do through using them instead of arguing on KZbin about which one is the same as another one, they would soon realise none of it matters if they're bad at photography in the first place.🤷🤓

[@okaro6595]

On wide angle the front element can be much bigger. My 11-22 mm lens has front element 33 mm yet the maximum entrance pupil at 22 mm f/5.6 is 4 mm.

[@miklschmidt]

I love when you talk nerdy to me.

[@geraldundone]

You win comment of the day! Love it. 😃👍💗

[@demasistudios]

Mikkel Schmidt 😂

[@helgividar]

Why making things simple when you can make them complicated? f-numer is just a ratio between diameter and length of a tube. If you extend the tube by roughly 40% or diminish diameter by around 30% you loose half of the light that gets through the tube. The same applies to lenses. F x 1.414 or D x 0.707 and you cut the light in half. That is equalivant to one stop or one exposure value. Changes in DOF is a side effect.

[@DavidJonesImages]

Hi Gerald. Great video thanks. Question: How do lens adaptors like Metabones speed booster affect DOF. specifically, on a M34 camera

[@m_hossein_n]

Would you please make your own note about how pixel zise affects depth of field if it does?

[@krby7274]

FSC sent me! 👌🏼👌🏼👌🏼

[@SB-mr2nk]

thank you, i learned something

[@jkeller4906]

Full Stack Creative sent me Woohoo!

[@johngwheeler]

Another excellently explained video from Mr. Undone. I was interested in the measurement of the "apparent aperture" taken by measuring the visible hole from the front lens element. How closely would this measurement agree with the theoretical N = f/D? i.e. if you have a 400mm f/4 lens would the measured clear aperture (from the front element) be close to or exactly 100mm? Or do the multiple lens elements make it impossible to simplify in this way? I own a number of (refracting) telescopes and there's generally a pretty exact agreement between the measured front element (objective) diameter and the measured focal length for the stated f-ratio. e.g. my 100mm f/7.4 scope does have the focal plane almost exactly 740mm behind the front lens. Telescope lenses are in general much simpler than camera lenses, with either 2 or 3 elements at the front, and in some designs one or two elements at the rear (in addition to any eyepiece or focal reducer/extender optics). Another question I've had for a long time is why lenses with relatively short focal lengths, such as the Sigma 18-35mm f/1.8 are so large, both in length and diameter? You would think (taking a simplistic N = f/D approach) that at f=35mm, the clear aperture would only be 35/1.8 = 19.4mm when wide open, and maybe slightly longer than 35mm. Obviously the front elements need to be larger to avoid distortion at the edge of the field, and I imagine the zoom mechanism needs some physical space - but why is the lens so long given the short focal length? I assume it's just the combined effect of all the lens elements that are converging & diverging to end up at the advertised focal length, but it seems very hard to estimate how big a lens will be based solely on the advertised focal length. Compare the 18-35 with a 24mm pancake lens which is minuscule in comparison, despite being in the middle of the same focal range.

[@geraldundone]

Thanks, John! I've held a ruler up to the front element before and found it to be surprisingly close to the expected diameter. So, yeah, you can. I know what you mean about the lens sizes. The attitude the manufacturers take toward optical formulas plays a big part. Some brands are okay with many corrective elements to reduce unwanted effects, where others go more minimalist. Sigma seems to prefer putting many elements in to maximize IQ when wide open.

[@youknowwho9247]

Interesting video for a channel that promotes MFT gear, since the information in this proves the general MFT marketing pitch of converting focal length to 35mm terms while citing physical maximum f-stop to be total bogus.