Shocking insight: AF is not a closed feedback loop!

Started Jul 18, 2003 | Discussions thread
Larry H. Smith Veteran Member • Posts: 6,270
Thanks Mishkin...

That's the kind of thing i come here hoping to learn

Larry

Mishkin2 wrote:
...you just should remember that with 10D you may get SOME of the
shots blurred by up to 4 pixels at f/2.8 (100% of 0.03mm CoC) and
proportionally more at faster apertures (e.g. 8 pixels at f/1.4). I
don't know the statistical distribution within this 0-100%
acceptable accuracy. Hopefully, it has maximum at 0% (perfect
focus, 0-pixel blur) and only a small tail at 100%. But some of the
shots are almost quaranteed to be as blurry as described. And it's
within AF spec!

With 1D/1Ds, theoretically things should improve by 3x. There still
could be problems in f/1.0-f/2.0 range.

It's best just to know these limitations and learn how to deal with
them. I for myself decided what to do when shooting in the 1.4-4
range - shoot a lot of frames while moving to your subject (when
it's close) or rotating focus ring (when subject is too far). I'm
going to use this technique extensively when shooting available
light and not worry about AF giving me blurry images.

And L lenses are still great. Use them now (with knowledge), and
enjoy your investment in the future when you will have a camera
with much better AF.

Larry H. Smith wrote:
Up-front: I haven't read (and probably couldn't have followed) all
the tech-discussion on the AF "issue'"in the various threads.

Does this new understanding (Thanks mishkin!)make it possible to
put into some reasonable number of words , a "best" way for the
user to maximize the AF potential of his rig, ...or a best way to
test/adjust "whatever" for that "best" performance?

(I mean when using whatever f-stop the photog WANTS to use, for
image reasons other-than-focus.)

This whole "what the camera can/can't do FOR you" thing is the main
reason I won't be happy till I have a pro-level camera that will
let ME do what I want, with a viewfinder that CLEARLY shows me what
is happening.

Thanks,

Larry

Mishkin2 wrote:

...a lotta stuff!

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