The AFMA myth.

Started 5 months ago | Discussions thread
Jack Jian Regular Member • Posts: 271
Re: The is AFMA is real and is not a myth
1

Distinctly Average wrote:

It amazes me that time after time users of this and other forums suggest AFMA based on little or no evidence that it is needed. Users see a shot that is soft, or completely missed focus and instantly tell the OP that AFMA is required. Some fail to even understand the “M” in AFMA stands for”Micro” and not massive. Even when the focus was off by meters, people still sat “do AMFA on all your lenses”. Sometimes they do not even ask if the shot was taken through the viewfinder or using live view.

To me the above is bad advice. Firstly it is just not possible from a single shot taken out and about that AFMA is required. That can only be done with some proper testing. Next it often misses any diagnosis of what may or may not be wrong with an image. It happens all the time on these forums. I have even seen it given as advice then it was plainly obvious the softness was caused by motion blur.

For most users, especially if they are using Canon glass on their Canon bodies, AFMA is not required. Canon have even said in the past it is a bandage and not a permanent fix. AFMA is a good tool to have, but not something to be relied upon, nor something to fiddle with based on flimsy evidence. In a lot of cases it can confuse the user even more, especially those with little DSLR experience. The adjustments only make a few mm difference in the focus point, but this can be enough to make things look terrible. I know one chap who returned his camera three times for service and each time was told nothing was wrong but given a new body as a good Will gesture. It was only when someone (a Nikon rep, this was a Nikon camera) sat down with him for a few hundred shots that it was realised the AFMA advice coupled with his lack of knowledge that was causing the problem. The guy was ready to switch brands but is now a happy Nikon user, and his AFMA is set to zero on all his lenses.

I firmly believe we should only suggest AFMA after a lot of questions have been asked and some proper testing has been done. It is not the panacea it is made out to be.

Canon do have a good guide on AFMA - https://cdn.static-bl.com/images/manual/Canon-AF-Micro-Adjust-Guide.pdf but I do think it should start with a bit more info regarding when and why.

AFMA is applicable if a lens is consistent, but off in factory calibration. For example, if a lens is inconsistent in AF (most third party lens does that), AFMA will not help. I have a Sigma lens which consistently front focus by a bit at the wider end for which the AFMA helps, dialed in for wide. Also, for some lenses, there is a tiny focus shift in closed aperture and for such, AFMA helps too. Also, some lenses have this inconsistency in certain distances.

There are many factors to consider AFMA. But like the OP said, directly advising to AFMA at a mentioned of soft lens is a bad advice.

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