Camera Autofocus Systems Explained: Phase, Contrast, Hybrid, DFD

Camera manufacturers have been utilizing different types of autofocus systems in modern digital cameras. If you’d like a primer on how each one works, here’s a fantastic 18-minute video by tech tester Gerald Undone that will bring you up to speed.

Gerald examines the systems in three cameras: the Canon EOS R with its Dual Pixel AF, the Sony a7 III with its hybrid phase-detection, and the Panasonic Lumix G9 with its Depth from Defocus (DFD) technology.

In addition to explaining how the major AF systems work, Gerald also helpfully explains strengths and shortcomings, giving you the knowledge you need to determine which AF type is right for your needs.

Here’s a table of contents for the video with the timestamps of the topics discussed:

01:20: Misconception: Everyone Thinks Contrast Detection is Bad
02:04: How Phase Detection Autofocus Works
02:55: How Contrast Detection Autofocus Works
03:50: Ways Contrast Detection Is Better Than Phase Detection
04:45: Ways Phase Detection Is Better Than Contrast Detection
04:54: The Pulsing You See with Contrast Detection
05:43: How Mirrorless Cameras Handle This Differently
06:43: How Camera Makers Decided to Solve These Problems
06:51: Solution #1: Hybrid AF & How It Works
07:30: Solution #2: Dual Pixel CMOS AF & How It’s Different
08:28: Shortcomings of Canon’s Dual Pixel AF
08:47: How the EOS R Addresses These Issues
09:10: Why Dual Pixel Is the Best for Video
09:42: 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

If you don’t need extreme autofocus performance, a contrast-detection system will be perfectly fine for you, Gerald says. It won’t be a limitation, and in many cases will even be a strength. For fast and erratically moving subjects, Gerald recommends a modern hybrid system. If you’re looking for an easy, well-rounded system that performs well in most situations, Canon’s Dual Pixel AF is his recommendation.

“But honestly, we’re in great times here when it comes to autofocus,” Gerald concludes. “There’s so many great systems and so much innovation that I think a lot of unnecessary hypercriticism is put on autofocus, especially when it doesn’t affect our bottom lines.

“Cameras aren’t perfect. Autofocus isn’t perfect. And we can’t demand perfection from them because of the very way that they function. What we can do is use them like tools. Understand how they work and try and find the best tool for the job and the best way to use it in that situation.”

If you found this video helpful, you can find more of Gerald’s videos by subscribing to his YouTube channel.

(via Gerald Undone via Steve’s Digicams)