AF problems on 50mm 1.4?

Started Dec 26, 2012 | Discussions thread
John Little
Regular MemberPosts: 293
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Re: AF problems on 50mm 1.4?
In reply to Sovern, Dec 29, 2012

Sovern wrote:

John Little wrote:

gdanmitchell wrote:

John Little wrote:

I got a 50mm 1.8 for Christmas. I had seen a lot of online talk about the AF problems, and mine definitely has them. Since a lot of people have talked about replacing the lens once, even twice, and still getting replacements with the same AF problems, I was wondering about replacing it with a 1.4. I haven't read anything online about the 1.4 having the same AF problems as the 1.8 but I just don't want to trade up ($200 up) for the same problem.

Does anyone have experience with this?

Thanks

Quite simply, if you have a new 50mm f/1.8 with "focusing problems," replacing it with a different lens so soon is probably not a very good idea at all. Basically there are two likely explanations:

  • The "focusing problems" are actually technique issues. It is hard to be more specific since you don't go any further than mentioning vague "AF problems" in your post, but unless you are certain that your approach is correct, replacing the lens will not solve the problem. Issues include camera stability, aperture selection, attention to AF point position, and more.
  • The individual copy of the lens that you have is malfunctioning. This isn't likely, but it is possible. If the "problem" is due to a malfunctioning or poorly adjusted lens, you should exchange it or send it to Canon for adjustment or replacement.
It is simply not true that this lens cannot focus right. Your first step is to determine, with some level of certainty, whether you have a problem with your copy or whether you need to address shooting technique issues.

Actually the focusing problems of this lens are extremely well documented and complained about all over the internet. There are a large number of people who have copies that they love and an equal number of people who say that theirs consistently mis-focuses. (Some of them use them anyway because the lens has qualities they like, and some of them apparently don't use them anymore.) And there are some who say they returned lenses until they got a good one.

And the way I determined that there were focusing problems was to set up the camera on a tripod, aim it at a ruled focusing target, take multiple exposures using a remote release, and compare (at 50% and 100%) the sharpest part of the image with DPP's little red box. I have repeated this in different locations with different light and the result is always the same. The aperture is irrelevant; the percentage of in-focus shots is always much smaller than the percentage of missed-focus shots.

The reason I started doing the testing is because my hand-held "real" shots were abysmally out of focus and I knew I wasn't that bad at using a camera. Unfortunately, I didn't find all the on-line complaints about the lens until after I experienced the problems myself.

A lot of people are also expecting to get tack sharp photos at f1.8. When shooting wide open with any lens you really need to machine gun the shutter and shoot your shots with multiple AF spots selected on your subject using the optimal AF point (the center).

F1.8 has such a thin plane of focus that it would be next to impossible to get in focus shots at it more than not.

I think the documented cases are due to a lot of beginning DSLR users buying the lens and expecting it to be like the kit lens and have a wide plane of focus wide open when in reality shooting from f1.8-f2.8 is very difficult and takes good technique.

Not only is the field of focus shallow at 1.8, the 1.8 and 1.4 are both known to be "soft" when wide-open. So that's just something you live with. I can live with soft; I can't live with missed focus, especially when the subject's eye is OOF and their nose is tack-sharp.

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