You’ve focused on the extreme end of your brand-new telephoto lens, and now you want to focus on something closer to you. The lens is billed as having some of the fastest AF in town, but when you try to focus on a subject much closer, the AF starts to hunt after focusing on something far away. You’re a little embarrassed now as this isn’t the kind of performance you’ve been expecting from a lens this expensive. But while the lens is only partially to blame, this sort of focus hunting happens often when you try to alternate focusing between near and far subjects. It’s an absolute pain at events and weddings when you’ve missed a key moment because the lens couldn’t lock focus on something quickly enough and spends what seems like an eternity trying to focus. It definitely feels a lot longer if your autofocus motor is noisy or, worse, squeaky. According to new reports, Canon appears to be working on some new technology that could entirely eliminate this issue for you.
Not Defocus Control
![](https://www.thephoblographer.com/wp-content/uploads/2024/06/defocus-4-1-770x650.png)
Before some of you get too excited, I must clarify things on one count. This isn’t a post about getting creamier than ever bokeh using what’s known as Defocus Control using lenses like the Canon RF 85mm F1.2 L USM DS or the Nikon 135mm f/2 DC. That’s a topic for another day. What we’re referring to in this article is the inability of many telephoto lenses to accurately nail focus when going from a far subject to a near one (or vice versa). It’s also something that’s plagued my Nikon 105mm f2.8 AF-S macro lens (and, unfortunately, it seems to have spilled over a little to the Z mount version). In fact, I feel it’s more apparent in macro lenses.
Defocus issues also arise when you try to focus on a subject when your lens is entirely out of focus. Either way, it’s a phenomenon that isn’t pleasant to experience, to say the least, and can often dampen your confidence in your lens. If recent reports turn out right, Canon might be doing something to help tackle or even eradicate this issue entirely in the coming years.
What Does The Report Say
CanonRumors has reported that Canon has filed a patent to help improve defocus issues with its mirrorless lenses. This appears to be more algorithm-related than related to hardware improvements on lenses and cameras. With sensor technology peaking right now, it makes sense that Canon is looking at software improvements to help fix defocus problems.
The English translation of the Japanese patent page states this:
PROBLEM TO BE SOLVED: To provide an imaging device capable of quickly focusing on a target subject even in a state where the target subject is largely out of focus.
SOLUTION: An imaging device includes; imaging means for imaging a subject; subject detection means for detecting a position of the subject from an image acquired by the imaging means; focus detection means for detecting a focus state of the subject; and control means for controlling search drive operation for driving a focus lens of an imaging optical system along an optical axis in order to search for a focal position of the subject using the focus detection means. The control means performs control so as to change driving speed of the focus lens in the search driving, based on a position of a focus detection frame for detecting a focus state in a screen and the position of the subject.
We hope the translated version of the flowchart on that page can help demystify the algorithm logic a bit:
![](https://www.thephoblographer.com/wp-content/uploads/2024/06/Screenshot-2024-06-15-at-12.45.34-770x1147.png)
The patent page also has a Claims section detailing 13 “claims.” Many of these are full of semantic jargon, but one of them appears to state that Canon will also consider the subject’s movement and speed when fixing defocus issues.
The image pickup apparatus according to claim 4, wherein the control unit changes the predetermined range based on at least one of a moving amount and a moving speed of the object.
I can think of at least one scenario where, as a sports photographer, this would come as a boon. Trackside at the horse races, focusing at the finish line and having just captured the winning horse with a 400mm lens, I need to immediately shoot closer at the winning connections who are celebrating for joy. Except that often, the lens can’t seem to get the proper focus in such a scenario as they can be standing just a few feet away from me. The sudden change in focal distance isn’t something it can keep up with, at least not before focus hunting for a few seconds, resulting in the instant joyful reactions being missed on my snaps.
How Can You Fix this Currently
![](https://www.thephoblographer.com/wp-content/uploads/2024/06/defocus-3-770x398.jpg)
Of course, one way to fix this is to pre-focus or manually get your focal distance closer to the subject you want to autofocus on, ensuring the lens doesn’t do any focus hunting. But that’s something experienced pros have been doing for a while now while many others stare at their lens with a scowl, wondering if their autofocus motors are about to die on them. While this isn’t the most practical of solutions, depending on what and where you’re photographing, it beats just indefinitely waiting for the lens to get it right on its own.
If you’re into technical photography, you’ll love the information on the patent page. It definitely looks like Canon will be doing their photographers a great service if they get this defocus algorithm right. I hope that other brands also pick up on this tech soon and eradicate this issue for good.
All images on this page are screenshots from Canon’s defocus patent page on the Japanese Patent Platform website.