New Olympus 17mm 1.8

Started 8 months ago | Discussions thread
madmaxmedia
Senior MemberPosts: 1,522
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Okay, I think I got it-
In reply to Anders W, 8 months ago

Anders W wrote:

In many earlier threads on the subject, I have pointed out that there are indeed conditions where the AF of the 20 will be slower than that of other lenses. One of them is when it hunts (although it is not more prone to hunting than other lenses, just slower when it does it). Another is when you focus between extremes, like from minimum focus distance (0.2 m) to infinity (but 0.75 to infinity as in my test is not a problem). A third situation for which the lens is not suited is AF-C (on Pany bodies it won't even be allowed to enter that mode) and a fourth is video (if you want to AF during a clip).

However, I am hard pressed to think of a situation where it is practically important to quickly AF from 0.2 m to infinity and as to hunting, the practical solution is simply not to allow the lens to hunt or hunt to completition. This is largely a matter of knowing your equipment, its limitations, and how to overcome them.

I think you point out right here pretty well why the 20mm gives less optimal AF experience than other lenses for many people, and why there have been various disagreements between you and some others.

It's easy to say, well just pick good AF targets and your lens won't hunt, or hey you should know that focusing from one extreme distance to another will slow down this lens so you should prepare accordingly.

But consider the type of candids one might be trying to capture with the 20mm (or other lenses.) You're in the backyard at sunset with the kids, the light is great and they are running around in the backyard and it's a beautiful scene. Great photo op- especially if you can be somewhat inconspicuous and not ask them to pose, etc. because you want to catch them in spontaneous moments and expressions.

In situations like this, focus hunting and racking focus from near/far and far/near are going to happen, due to unpredictability of subject movement, low light, only reasonable contrast in terms of catching detail on faces, etc. It's easy to end up racking focus when you try to focus on child, but he's moving and so you miss and the camera focuses on the distant background, etc. The end result is that there's a good chance you are going to miss more shots with the 20mm than other lenses, even if you're trying to be careful and use good contrast AF technique.

So I don't disagree at all with your testing methodology and results. When there is no hunting and you're not racking focus over distance, the 20mm is actually pretty fast! But as you point out, there are factors that can lead to a slower overall AF experience with the 20mm lens than with other lenses. And these factors may come into play more often than not for some people, or in some situations.

I understand all of the above. The main reason, however, that tests are insufficient is that there are too many potentially different situations for tests to cover them all well enough. Consequently, I too listen to the experiences of others. Sometimes, however, I find reason to question that reports about such experiences are valid descriptions of the objective facts. As I hope you realize, the step from subjective experiences to objective facts is sometimes a very long and complicated one.

The 20/1.7 and its AF behavior is a case in point here. I have seen quite a few forum members recognize, after discussing the matter in detail, that perceptual complications play a part in the impression that the AF of the 20 is slow. One of these is that you hear the lens AF (in sufficiently quite surroundings), which is likely to strengthen the impression of duration. Another is that the slow hunting behavior is what is most likely to make a lasting impression.

I agree with all these points too.

Actually, knowing about the good and bad aspects of the 20mm AF performance, will probably help me try to maximize AF performance. And that may lead to a subjectively better experience, and opinion of the lens AF.

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