How Autofocus Has Evolved and How to Choose the Right System

Autofocus systems have evolved rapidly since the technology first emerged in the mid-70s. Understanding contrast detection, phase detection, and dual-pixel is a complex business, but might be critical to choosing the system that best suits what you shoot. This intense video covers pretty much everything.

If you're unfamiliar with how the various systems work, sit tight; this comprehensive video from Gerald Undone runs through the processes behind the various systems and explores their various advantages and disadvantages. In addition to a surprisingly interesting history lesson, you should also emerge with an understanding of which system best suits your subject and style of shooting, both for photography and for video. 

Gerald references three very different cameras when explaining the various systems and their latest implementations: the Sony a7 III, the Panasonic Lumix G9, and the recently released Canon EOS R. Mirrorless technology has seen a significant change in the potential for autofocus, not just in speed and accuracy, but also in additional features such as tracking and eye/face detection. If you're pondering a move away from a DSLR, it's well worth investigating autofocus before choosing a camera.

As with many aspects of photography, there's no one-size-fits-all solution, and there's no simple argument as to which system is best. Instead, there are different options that might be better or worse for what you shoot, with different manufacturers choosing to prioritize certain elements over others. Do you need accuracy or speed? Do you need smooth transitions or better tracking? Or do you need something that is the best of both worlds?

You might want to plug in the headphones and take some notes as the sheer amount and rate of information here is a little intense.

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9 Comments

Spy Black's picture

Good stuff. Essentially you need camera x for a, y for b, and z for c.

Paul G's picture

I don't have the best part of 20 minutes to potentially waste on a video that may or may not tell me something new, why not do this as a written article which most literate people could read in 5 to 10 minutes.

Andy Day's picture

Yep, definitely something that we can consider for the future. My knowledge of AF systems is pretty limited so probably best that I leave it to someone else. For now, however, Gerald kindly created a table of contents that I hope will be of use:

1:20 - Misconception: Everyone Thinks Contrast Detection is Bad
2:04 - How Phase Detection Autofocus Works
2:55 - How Contrast Detection Autofocus Works
3:50 - Ways Contrast Detection Is Better Than Phase Detection
4:45 - Ways Phase Detection Is Better Than Contrast Detection
4:54 - The Pulsing You See with Contrast Detection
5:43 - How Mirrorless Cameras Handle This Differently
6:43 - How Camera Makers Decided to Solve These Problems
6:51 - Solution #1: Hybrid AF & How It Works
7:30 - Solution #2: Dual Pixel CMOS AF & How It's Different
8:28 - Shortcomings of Canon's Dual Pixel AF
8:47 - How the EOS R Addresses These Issues
9:10 - Why Dual Pixel Is the Best for Video
9:42 - Why the Modern Hybrid AF Systems (Sony) Are My Favourite
10:10 - But the Panasonic G9 Is Still Faster because of DFD
10:20 - Solution #3: What is Depth from Defocus & How It Works
11:42 - The Limitations of Depth from Defocus
12:33 - Why Some Lenses Perform Better Than Others
13:00 - The Importance of Autofocus Points & Coverage
14:13 - Why You Shouldn't Use Focus & Recompose
15:42 - Practical Applications: Which AF System to Use When
17:22 - Final Thoughts - Most Autofocus Systems Are Great

Jerry Norman's picture

Paul, your response is what I think with many of the videos that show up here on FS. That said, I found this video excellent because Gerald did a really good job incorporating animations and videos to illustrate many of the points he makes. He put a lot of work into this and by the end I was appreciative of the effort as it really helped me understand the differences in the focus technologies.

Thomas Wollburg's picture

Wondering why Nikon does not exist in his world? Quite content with my D750s AF.

Philipp Pley's picture

Your Nikon D750 is a DSLR camera, he's only comparing mirrorless systems.
All DSLR cameras use phase detect sensors when you're using the viewfinder, which yes works an absolute charm.
This video is specifically about the AF in live view, i.e. what mirrorless cameras solely use.

Nikon Z cameras also have phase detect AF, but this is the first time Nikon has ever used the technology, and I think (not being scientific here, just based on some reviews so far) that this still limps behind Sony and Canon who have heaps more experience and patents in that field.

Jerry Norman's picture

Thomas, I love most things about my D750 but the live view focus performance when shooting video is very poor in my experience, even if the camera and subject are stationary.

I miss he EYE controlled focus from the Canon EOS3. For me it worked very well. For wildlife Photographer Art Wolfe it worked very well. For some, not so well.
Why can't Canon use updated technology to get this working on the newer digital cameras?

Very informative video. I don't always make time for such things, but this guy, Gerald Undone, seems to know his audience. I can't imagine a tighter-edited video--I think he edited out any instance of drawing breath or any pause longer than 0.25 sec, LOL!

Anyway, great stuff. I think the future will be very interesting with regard to AF as cameras gain more processing power and predictive AI functionality (see the camera on the Pixel 3 for instance).