The AFMA myth.

Started 5 months ago | Discussions thread
poppyjk Contributing Member • Posts: 757
Re: The AFMA myth.

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 - but I do think it should start with a bit more info regarding when and why.

The highlighted statements are not accurate and are misleading coming from someone who claims to be authoritative on the subject of AFMA.

I am one who does AFMA on all new lenses and/or DSLR change as a part of routine new equipment quality checks. Canon's new cameras and lenses seem to have greater consistency and require less adjustment.

My L lens adjustments on a 5DsR:

24-105 f4 L W +5 T -1

70-300 L W -2 T +7

24-70 f2.8 II W -1 T -1

16-35 f4 L W 0 T +2

35 f1.4 II L +1

100-400 II L W 0 T 0

A close friend of mine is a bird photographer. She has an excellent copy of the Sigma C 150-600. When she changed bodies from a 70D to 80D everything was out of focus. It required AFMA of W -5 and T +7. At 600mm with the subject at about 200 feet the T +7 adjustment moved the focus point about 6 feet. Not a 'few mm' in my estimation.

Here is a demonstration of the difference an AFMA adjustment can make at 0, -10, and -20 to significantly demonstrate that front focus correction measured in feet not millimeters can be achieved.

The subject is about 175 feet away and shot at 400mm, f5.6, an 1/400. This is a 100% crop from a 5DsR with the 100-400 II that is an excellent copy with no AFMA required.


AFMA -10

AFMA -20

I am sure that someone can find faults with the demo and/or draw different conclusions.  Fine, this is a discussion.

"Well done is better than well said" - Benjamin Franklin

 poppyjk's gear list:poppyjk's gear list
Canon EOS 5DS R Canon EF 24-70mm F2.8L II USM Canon EF 16-35mm F4L IS USM Canon EF 100-400mm F4.5-5.6L IS II Canon EF 35mm F1.4L II USM +5 more
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