The AFMA myth.

Started 5 months ago | Discussions thread
OP Distinctly Average Contributing Member • Posts: 595
Re: The AFMA myth.

poppyjk wrote:

Distinctly Average wrote:

First your test shots, maybe try with a sloped ruler and a proper target and you will see what the actual difference it makes. Why do you think the focus char tools and focus pyramids are not 6-8 feet deep? Maybe have a read of this -

I beg your pardon! Are you denying the reality that my sample photo focus changes between zero and -20 is about 6 feet? I purposely selected a scene at 175 feet with a slanted brick wall to provide compelling visual information which is more valuable and accurate than a 'sloped ruler' at 50X the lens focal length on the LensAlign tool.

I have used LensAlign MkII extensively as well as some other 'for sale' tools. In my experience using those tools with their inherent limitations often translates poorly to real world actual focus accuracy performance, especially with telephoto lenses. Nothing is more accurate than adjusting AFMA at the actual expected subject distance with a slanted foreground and background and from a tripod. If you have not tried it , I suggest you do.

You appear to be miss-understanding the whole point of the post and thread. AMFA can be a good tool. It is however given as advice based on very little actual evidence that there is a problem with AFMA. I have seen many times both online and in forums just how often it is offered as advice when other things are obviously amiss. If the basics are not correct, all AFMA is going to do is confuse things further, double so if AFMA is not fully understood.

I will ignore your dismissiveness. I understand and agree with most of the points that you make.

I completely disagree with "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”. and "The adjustments only make a few mm difference in the focus point, but this can be enough to make things look terrible." Are you really saying that a photo taken of a subject 200 feet away with a 600mm lens is only affected by a few millimeters when AFMA adjustments are made?

These statements are factually wrong for photos taken at distance in the real world. The reason for my post was to point out this inaccuracy so that those reading the thread would not be misled. The samples were included that actually show the differences are in feet not millimeters.

You appear to believe that there can not be several feet of difference in the focal point at long distance due to an AFMA problem. Do you actually believe that the several feet of distance shift is not represented factually and accurately in my sample photos?

AFMA - Auto Focus Microadjustment. Look it up then tell me that it is “factually wrong” that I used the word “micro”? I

In your test the camera moved between shots, the camera did what it is supposed to do and picked it the nearer object. Your test fails to prove anything. Please actually read the article from a well respected source, it give some good advice on testing. If you don’t believe that source, or indeed Canon then at least test properly yourself with a target an ruler. You will see what AFMA actually does. A fixed target in good lighting is important, and a scale to measure it by.

I think you also miss understand that AFMA does not actually change the focus point, just the average bias of the focus point.

I quote the digital picture here - “

Canon specifies the precision of the AF system to be within one depth of focus for a lens’ maximum aperture for standard-precision AF points, and within 1/3 of the depth of focus for a lens’ maximum aperture for high-precision AF points which are activated by faster lenses (f/2.8 center point on most bodies, f/4 center point on 1-series bodies). One unit of AFMA equates to 1/8 of the depth of focus of a given lens’ maximum aperture.”

And just for some figures in a nice graph here are the results showing average adjustments taken with Canon glass over 5 years collated by the people at Reikan -

To me that is quite a glowing review of how accurate Canon glass and AF is.

I do not and never have professed to be authoritative on the subject of AFMA or indeed anything. However I do have enough experience to tell the all too often the advice given to AFMA it out of place. You cannot determine from a single shot that AFMA is out of whack. You can not tell beginners to AFMA based on weak evidence. The whole AMFA experience confuses so many people who simply want to go out and enjoy their hobby. People with little technical background read AFMA advice given out of place and get in a whole heap of mess because of it. People look for a reason that their images are off focus, often blaming their kit and AFMA provides that crutch. Far more often the problem is actually easy to solve with better technique and knowledge of appropriate settings on the camera.

There are other things that aggravate me, such as those that dismiss stunning shots as “too noisy”. I know a few birders who have wasted so much time and money because of those sorts of comments. That is a subject of its own though.
Just enjoying photography

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