Contrast detection autofocus doesn’t suck as much as you think and here’s why
New cameras get a lot of hassle over their autofocus systems. Either it doesn’t have Eye AF, or it isn’t dual pixel or it’s not phase detection. But what do all of these things mean? And I don’t just mean what are the technical differences, but how and why does this matter in the real world? And to whom does it matter?
That’s what this video from Gerald Undone covers, in probably the most unbiased way I’ve ever seen. Autofocus technology is evolving rapidly, and he covers just about all of it. He explains how they work, the pros and cons of each, when the system your camera uses matters and when it probably doesn’t.
It’s a very interesting video and demystifies a lot of the questions around the different autofocus systems available while busting a few myths. He covers a lot of topics, but here’s a table so you can quickly go to the bits you’re interested in – although I’d really suggest watching the whole thing.
- 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
As you can see from the list above, it’s pretty in-depth.
Basically, though, if you don’t need high-speed tracking and movement, then contrast detection can work just fine. In fact, it can even be better as it’s typically more accurate than phase detection systems. That accuracy is why it’s still used in hybrid autofocus systems. And it’s hybrid systems like the latest generation of Sony and Fuji cameras that Gerald recommends if you do need fast action. For overall general purpose use, Canon’s dual pixel autofocus comes at the top of Gerald’s list as the best balance of speed vs accuracy.
But there are times when the autofocus system really doesn’t matter. With landscapes, still lifes, product photography, for example, all of the different systems are going to perform rather well. So if those are what you primarily choose to shoot, then what autofocus system a camera uses probably shouldn’t be high up on your list of priorities when picking a new camera, and switching from one system to another probably won’t offer you any real advantage.
We’re in great times here, when it comes to autofocus. There are so many great systems and so much innovation that I think a lot of unnecessary hype or criticism 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 to find the best tool for the job, and the best way to use it in that situation.
So, autofocus systems aren’t as clear-cut as “this is awesome, that sucks”. That might’ve once have been true, but not anymore. All of the systems have come a very long way in the last decade or two, and they all have their strengths and weaknesses.
Which system gives you the results you need for your photography?
John Aldred is a photographer with over 20 years of experience in the portrait and commercial worlds. He is based in Scotland and has been an early adopter – and occasional beta tester – of almost every digital imaging technology in that time. As well as his creative visual work, John uses 3D printing, electronics and programming to create his own photography and filmmaking tools and consults for a number of brands across the industry.