The AFMA myth.

Started 5 months ago | Discussions thread
OP Distinctly Average Contributing Member • Posts: 600
Re: The AFMA myth.

Andy01 wrote:

DavidArmenPhoto wrote:

Andy01 wrote:

I think that AFMA is useful in general, and can be EXTREMELY useful in some cases. I have tested every lens I have owned with 70D and 6D ii (the only two bodies I have owned with AFMA), and every one of them needed some degree of adjustment, often not major though. Lenses include Canon 24-105L, 24-105L ii, 100-400L, 100-400L ii & EF 35 f2 IS, and a Sigma 17-50 f2.8 (which I would rather not even talk about).

I do agree though that there are people here who blame every missed focus on AFMA (or lack of), and there are people here who seem to be much better than me in spotting front or back focusing (a recent example of an orca's fin that was not focused correctly - people spotted front focus on relatively calm reflective water, and suggested AFMA - better than me - AFMA may have been required or have helped, but it was pretty hard to tell from the image in question).

And a mention above of a couple of mm - a couple of mm can make all the difference when trying to shoot a bee in a flower at 400mm


What’s wrong with your copy of the Sigma 17-50? It’s a pretty sharp lens for its price actually.

I tried 4 copies in a store before I found that was sharp in the corners, so there certainly is (or was - a few years ago now) significant copy variation.

I did use some AFMA to get the focus more accurate, and often it was accurate and I got nice sharp results.

The problem I had was that too often I would get erratic inaccurate focus (either OVF or LV), where photos would be quite soft (even in the centre) for no apparent reason. It did seem to be worse when used wide open at f2.8, but it wasn't exclusively f2.8.

So when it got the focus right, it was good, but too often was soft so I sold it. It did put me off 3rd party lenses a fair bit.

I have over the last few years read quite a few people seemed to have similar experiences with this particular Sigma lens (and an awful lot more with a range of other Sigma lenses), so I don't think it was an isolated case.


So a case where AFMA would not have worked. As you know, it has no effect in LV but you,experienced the erratic focus there too. I remember having the same issue with a Sigma I one owned.

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