Autofocus for GEEKS: Phase vs Contrast (WARNING: Intense detail)

First 500 get a 2-month free trial to Skillshare: skl.sh/northrup14
Tony gets DEEP into how mirrorless and DSLR cameras autofocus with Contrast-detect autofocus (CDAF) and Phase detect autofocus (PDAF). You'll understand why DSLRs sometimes need micro-adjustments, why CDAF is slower (but more precise), and why CDAF cameras (like the Panasonic GH5 and S1) have focus that hunts in and out when recording video.
Music: share.epidemicsound.com/Tony

[@MrPotatoemouse]

This is exactly the level of detail I appreciate! Very well communicated even for those of us with a shaky grasp of science. Thanks

[@speterlewis]

Just when we thought Tony'd reached the apogee of photo nerdness. This was utterly fascinating. Thanks for going the extra mile to help us understand our beloved passion!

[@OpCharlieBravo]

This is why i like this channel more over others, especially when Tony geeks out like this. It's a great learning experience that gives a deeper understanding of cameras work, which can only improve the way you shoot. Most channels are basically a "wash and repeat" of photography. If you want to become a knowledgeable pro photographer, this is one of the best channels to learn from because it covers a lot of aspects of being a photographer, not just about a camera and lens but everything from the obvious like lighting, models, posing etc... to computer hardware set up, website ... to boat loads of useful tips.

[@Razor2048]

One thing is that contrast detect AF can be improved, as companies come up with new methods of subject tracking. For example, instead of pulling a Nikon and setting the CDAF loop to a 1 second delay, some will use a delay free method and instead establish a baseline of out of focus that is allowed before it attempts to focus again, thus with minimal movement, there will be no hunting, and when a subject moves, some basic logic is used to determine if something is moving towards or away from the camera, and thus will make a smarter choice as for when to adjust. They will also keep track of peak contrast levels, in order to avoid the need for an overshoot. Some CDAF algorithms can achieve almost follow-focus type behavior, the issue is that most DSLR makers refuse to modernize their CDAF. For example, Nikon's CDAF still does not use the accelerometer data to measure camera shake and use that data along with the shutter speed to determine if camera shake is causing motion blur and then pause the CDAF loop until CDAF can be reliable used to get focus. Some smartphones will do this and it helps prevent situation where if there is a lot of camera movement that the camera does not completely lose focus or hunt endlessly. Most DSLR makers refuse to bring over some of their tracking algorithms related to motion estimation when it comes to subject tracking. This is why on a camera like the D7500, subject tracking in video always lags behind the movement of the subject. On the other hand, if using the phase detect system, even though it shuts off while the while the pellicle mirror is being moved, it can still get accurate focus of a fast moving subject, and that is because the camera estimated how fast the subject was moving prior to taking the image, and then used that data to calculate a subject distance that is likely when the sensor is finally exposed. This can be done with CDAF also, and some cameras already do this, but DSLR makers that have a separate PDAF sensor, never implement these features into their CDAF system like how the cameras using modern CDAF only systems are doing.

[@MNDBC]

Coming from an Electronic technology background before going into IT, this video really helped me to understand how AutoFocus works. Thanks so much for sharing and explaining how it works. Keep on geeking!

[@alifonso1981]

You're always a few steps ahead from everyone else but you stay humble enough to drag us with you. Thank you!

[@drewherbi]

I am a technical nerd to the max, and I LOVE videos like this. Thanks Tony!

[@samartography]

This is Amazing Tony! This is the reason I live and respect you both and your channel. Always good to hear your thoughts and ideology in photography. Keep doing what you're doing. Wish you the best health and success!

[@MartianCitizen]

Thanks Tony. Always interesting to hear how things work. As always, keep up the good work and keep em flying...

[@LeoinFrance]

Wow!! This is one of my most appreciated videos from you channel since a while!! Thanks so much for touching this subject in such an accessible way.

[@michaelscaplis]

Tony going full on nerd but this is one of the first times I saw such an easy to understand explanation of how focusing works. Kudos!

[@st.michaelthearchangel7774]

Still lost. 😄

[@gillescoutlee2379]

Keep on the good work! I think it is very stimulating to understand not only 'how' it works but also 'why'...One of the rare sites where practice and theory are dynamically working together. Excellent!

[@TJuice1986]

I signed up for the free 2 months on skillshare. I’ve gotta be honest, it’s pretty amazing. Huge thank you to Tony for the free 2 month trial!

[@scottster8858]

Thanks Tony! I've been looking for a clear and concise explanation about his for years.

[@patrickcarrierephoto]

Your explanations were spot on, "in focus" :), especially on how the focus sensors are integrated into the main light sensors of mirrorless camera was an eye opener. It will make me think twice if I ever wanted to switch to a mirrorless camera in the future.

[@carlraetzsch]

Dual Sharpie Autofocus Tutorial, by Tony Northrup. Nice tutorial and I do enjoy learning how things work. Thanks Tony!

[@karls6802]

Excellent clear explanation of a complex subject and often misunderstood. Thanks

[@nnn-pr3vr]

I searched up how phase detect works cos i was curious, perfect explanation video, the engineering is incredible

[@claudiowed9086]

That was awesome, thanks for giving us this kind of technical insight! I'd love to see more of this kind of videos!

[@scarborosasquatchstation1403]

WOW !!! Tony explains auto-focus with math's Pythagorean Theorem , that even non-geeky nerds can fully understand to learn this important lesson..... for all camera owners !!! Thanks Scarboro

[@fredastaire6156]

This is absolutely fascinating; I was actually able to follow since college physics is still fresh in my mind. Thank you for making such an informative video.

[@malcolmpierce825]

Thanks! Great stuff! You're always scientific. I appreciate that.

[@heythere9380]

"Nerdthurp" does it again:Tony presents a topic i don't care to truly understand and it keeps me watching. That diagram also replayed a bad flashback to HS trig class and watching my G.P.A. go south.

[@antonioPaulino]

Great video. Pls bring more of these technical ones.

[@JS-wz3km]

Love the camera history and the knowledge. Thanks for the link!

[@JamesLoudon]

Thanks Tony, very well explained. And I am much more clued in now.

[@EntropicRemnants]

Wow. Thought I understood it before --- wonderful exposition of the details, thanks.

[@JeremySmith23]

Your latest videos are looking so good. I’m loving the lighting

[@ScottVincentPhotos]

That was surprisingly interesting and helpful - Thanks Tony!

[@standhd]

Goodness, I thought I a NERD....I quickly lost my PHASE DETECT lock on your explanation when you went in DEEP on the subject matter. HOOK EM!

[@l353a1]

That's great. I enoyed the detail. Please keep making such detailed explanations.

[@joewall6608]

class video and great explination tony, would love to see more

[@djkeopsss]

Great stuff! Now i finally understand the difference between CDAF and PDAF. Thank you.

[@AIPTutorials]

10 years+ of using DSLR and still blown away at just how complex and sophisticated they are.

[@leonard-teo]

Absolutely fascinating Tony, thanks!

[@shawnbelluigi16]

Fantastic. I enjoyed all the nerdy explanations

[@imnotoriousnate]

really love these videos! and thanks for the free 2 months!

[@bird271828]

Tony, I love this episode. Thank you for the explanation.

[@lyfandeth]

Kudos Tony! Now so much more makes sense about new dslr vs mirrorless vs old school!

[@hakeem-ji]

well explained tony.. the idea got clearer .. and more in-focus in my head :)

[@KoalaMeatPie]

I never thought I'd correct Tony effing Northrup, but, The first SLR with built in Autofocus was the Polaroid SX-70 Sonar in 1978

[@JCole78]

KoalaMeatPie yep, and it was followed by Pentax with the first 35mm SLR Camera about 3 years later with the ME-F. The Minolta 7000 actually didn’t come out for another 2 years after the Pentax.

[@raybohn7]

Yes, but you would need to gently stroke the case and speak friendly words to insure success.

[@johnhjic2]

All in all Tony one of your more interesting videos and a great explanation. Thank you.

[@ZenGeekDad]

I *really* appreciate the much-needed perspective on dual-pixel autofocus, since all other comments I've seen hail it as infallible and unmatched. As a lifetime R&D engineer, I can vouch that a huge part of design is understanding error propagation/measurement precision. So, moving the parallax of the phase detect distance measurement down to the width of one pixel seems very risky indeed. No doubt, Canon counters that some by leveraging statistics from so many pixels in aggregate. And combining that with software for subject (face) detection, should improve that (which pixels to average, which to ignore). Still, all theory needs to meet data, and your observation of focal confusion at long focal lengths says a lot. At what focal lengths does the DPAF tend to be act more reliable for you?

[@1978jra]

Wow! So much new information. Nice job!

[@KoalaMeatPie]

I love these nerdy deep dives, just like the ISO / Gain video you made. I would like some more. More Porridge

[@TonyMacina]

Great video, and makes it easier for people to understand why Pana have just tried to improve CDAF. Ultimately it improves image quality and accuracy, but makes it weaker for video autofocus. I'd say the S1R is probably the best studio camera along with the D850 because of the issues with phase detection on sensor.

[@jammin023]

Indeed. It's kind of ironic that Panasonic tend to be more lauded for video than stills, when their AF system is actually better for single-AF stills rather than continuous video AF. They have made great strides in improving it, and an advantage of being mirrorless is that they can use computational scene analysis in order to predict movement... but without PDAF it will always have the problem of having to pulse in and out to check for better focus. I love Panasonic cameras in every respect except for their refusal to provide PDAF. But it's nice to have a choice I guess.

[@kayzphotography3678]

Very interesting and educational ... well explained and easy to understand 👍

[@mk0x55]

Great content, thanks Tony! :) It's always cool to learn how things work to understand their limitations better out in the field and in general. When it comes to PDAF, I guess the limitation is also precision of the arithmetics the camera is capable of (perhaps you mentioned...), as well as how to convert the pixel values (including noise) together with their positions into accurate distance information. I'm actually switching to good quality manual focus primes a lot nowadays, and find that even just through an optical viewfinder (enhanced with a S-type focusing screen), I'm often able to nail focus much better than the autofocus used to (although not as consistently, unfortunately).

[@sergioserramusic]

Cool video, I already knew most of this stuff but it’s always good to refresh some notions ;)

[@JuanMartinezJones]

Thanks for such a good explanation, Tony. I always wondered why people thought mirrorless systems were worse in focusing than DSLRs and now I have a proper answer with science for that. Incredible video, I am loving you nerdy stuff, one of the main reasons I have started following this channel long years ago. Good quality content delivered in understandable explanation from tech to art. Congratulations!

[@NiltonVolpato]

I don't think that's the takeaway from this video, though. PDAF has pros and cons for mirrorless vs DSLRs, it's not that PDAF on a DSLR is always better. For instance, it can get out of sync on DSLRs and needs fine tuning, mirrorless don't need that. Also, mirrorless can do PDAF while recording video. Also mirrorless allow for autofocus to cover a larger area of the sensor. And many many other pros and cons.

[@BatAskal]

Mirrorless systems tend to use hybrid AF system. In addition to PDAF on sensor itself, since his video illustrates how imprecise it can be when the angles hitting the sensors are wide apart to resolve the image, it also uses contrast detect to finalize the focusing process.

[@arijitghosh6378]

Good stuff! Keep 'em coming.

[@tetraskele9621]

Great little lecture on modern AF. Fascinating. Thank Tony!

[@Dustinrhoades]

Fascinating Tony. Thank you

[@paololarocca7684]

Thanks Tony, interesting and in depth explanation....

[@clintjohnson2460]

Took me a few seconds to figure out what the topic was,, but I'm so glad I clued in and pulled up a chair--great , concise explanation and stuff every (at least) every advanced amateur and hobbyist and pro should know--I know the cameras software can usually compensate for some of the distortion and vignetting we get ...Hust wondering if there are software programs that can recognize and attempt to correct banding,,,,I see it from time to time...

[@vusalterego]

Gary Friedman has some great videos demonstrating AF capabilities and limitations, including how non-cross-type AF points aren't able to pick up horizontal lines. Thanks to your phase detect explanation, it totally makes sense why this is the case.

[@travissaunders4686]

I just love the title. Like we didn't figure on a Tony video having "intense detail". LOL What a geek, love it.

[@kiliandietrich8526]

Always appreciate these videos. The more you know about the physics of photography, the better you will understand how to spend your money and why things cost certain prices. Cool stuff ;)

[@AtomicArcherGuy]

This is useful to know. Thanks Tony!

[@SassePhoto]

Nicely explained just right for me. If you wish I can help you revising your diffraction vs sharpening clip as this is my background

[@djszido]

Thank you for this excellent video. I was always wonderig how these systems work. :) I would be also interested in a video about focus peaking.

[@Alfredolunafoto1]

Great video as always. Thank you

[@carlseibert9015]

Excellent. Very nicely done.

[@PaulKretz]

This is *brilliant* ! I love such stuff!

[@AnindyaMitraDigitalStoryteller]

Wow that's highly detailed just as the title says! Please, please, do a video on the signal to noise ratio in mirrorless cameras, nobody talks about this..like ever

[@azizurrahaman2101]

Very nice explanation. Finally I understand pdaf.

[@truthsurfer808]

Great video! Love the nerdy stuff!

[@bladerunner_1969]

I love the science! Thank you Tony!

[@rubenremus5649]

Nice explanation. Thank you!

[@ChimaChindaDev]

I found this video so interesting. Great work. We're still waiting for the Capture One video though :)

[@robertpapps3618]

Great explanation, thanks much!

[@RedTick2]

Werner may be right, but honestly if I see a video from Tony that has terms I don't recognize I get excited that I am going to learn something new! Another great video Tony, keep them coming!

[@richardactor]

Tony, you are one smart dude! I love these videos!

[@demasistudios]

Tony just got undone ? Are you hiding in the back somewhere Gerald?

[@matthewbrooks1589]

You looked like you really enjoyed talking about this subject 🙂 it may take a few watches to process it for me though.

[@pjf7943]

Educational and nicely done.. Thank you..

[@clmims100]

I keep my big Nikon 810 and 610 with the Nikon Flashes for indoor Photography because of the infrared emitter on the flash or from the special cord. You can shoot in a black room and nail focus every time. This has been true from the film days. I have gone through every other system and never matched the ability to nail focus for event photography. Aftermarket flash never work as well as the OEM flashes like the Nikon 910 and Nikon 600. I find that higher speed prime lenses really work better. My Nikon 24-110 f4. has much more accurate focus than a 24-80 with a smaller wide open F Stop.

[@boonyarithdumrongpalasith5501]

Perfect Tony, Thank you.

[@ThisWayUpTravel]

Thanks so much for this video! I've been wondering what the heck phase detection af for a while, now I know! LOVED geeking out on this! Just as a bit of constructive feedback, you might want to look at some DeEsser effects to reduce the sibilance in the audio.

[@danev1969]

There is a balance between knowing and the need to know. Thanks Tony for the insight. I will never buy a DSLR again (having moved to mirrorless about 4 years ago), but I admit to admiring the Nikon D850 because of its superb focus capability (said by a Sony user...)

[@legacyfitness7469]

I love this nerdy high tech to the pixel explanatory videos 💪

[@davidgriffin79]

You wouldn't need the hypotenuse for the two right-angled triangles you could use tan(alpha/2)=(opposite/2)/adjacent => adgacent = (opposite/2)cot(alpha/2), where the adjacent is the distance from the mid-point between the eyes to the subject, alpha is the angle subtended by the line between the eyes and the opposite is the length of the line between the eyes. Also, I think what you were trying to say is that as the phase detection sensors get closer to each other the angle that they subtend at the subject gets very small. The further away the subject, the smaller the subtended angle, so things get trickier with long lenses

[@aengusmacnaughton1375]

Cool -- thank you for explaining that in 15 minutes -- not a waste of my time at all!

[@dzllz]

Omg I love those geeky videos. Amazing stuff!

[@7medo7]

Very good video, thanks!

[@MrPsylocibine]

The best info for a geek, comes from another geek. Thanks Tony

[@geraldundone]

I thought I made this video already? Haha. 😜 Enjoyed the vid, Tony. Love the nerdy stuff!

[@meenakshisundaran69]

I think you love nerdy stuff more than him. That's why I subscribed your channel way back!! 👍

[@mediamannaman]

And now we have two really good technical teachers presenting. And you each communicate in a different style. Watching both improves my overall comprehension. But you knew that, ergo, the "Haha."

[@MyekalBenham]

Was thinking the same thing. As in you made this video Gerald.

[@fellowcitizen]

but y'uroe Caidaann, we culndo't fluly unedrsantd waht you wree sniayg in taht aiencnt dialect ;-)

[@dmacrolens]

It's not funny.

[@SohamDas1995]

Outstanding video

[@ahmonon4352]

Great video, this is why you're the best in KZbin

[@lylestavast7652]

Nicely done. My Nikon D750, I have to use liveview if I want anything really sharply in focus at even modestly open f-stops (like 5.6 or 8 on an f4 lens). Doing calibration diagrams and fine tuning sans LV, never results in focus nearly as good as the LV lockin... it's slower and necessitates using a tripod for the most part, but much of what I shoot is static and done tripod anyway - or at higher f-stop using viewfinder focus system... Another path I sometimes take is use viewfinder focus but focus stack and let software sort it out, even handheld it works out better.

Wow such dirty mirror in that D850 Tony :D Nicely explained in that video, I'm sure everyone can now understand the differences.

[@pathway1]

That was intensely detailed on the details of autofocus

[@BiggMo]

Thanks Tony- now I know how to go build my own camera. Watch out Sony, Canon and Nikon - we’re coming for you. On a serious note - take a good look at the facial structure of competitive target shooters. They have a tendency to have asymmetrical eye placement. That asymmetric difference provides their brains more complex data.

[@stuartrushworth5487]

Fascinating. Thank you.

[@chrisfeatherstone9691]

Great job explaining! 🤓

[@Edgarbopp]

Great content!

[@rodrigodepierola]

Any video that mentions the Law of Sines is a good video.

[@donstravelsandrants.]

Amazing information.

[@maxlohrberg5317]

I just love those classic, "nerdy" Tony Northrup videos

[@ZKaiLe]

One of the best explaination of af!