Canon's Chuck Westfall offers microadjustment tips.

Started Dec 11, 2008 | Discussions thread
Dietmar Fichter
Senior MemberPosts: 1,655
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Re: Range/FL can change where the AF MA needs to be set. Test them all, not just one
In reply to Nadrek, Feb 6, 2009

Isn't it just amazing how photographers over the years even survived without microfocus adjustment when this technology didn't exist. It must have been hell for any lens to be in focus on a camera body. I for one have a 20D, 30D, 40D and a 50D and all my lenses focus just fine on each body, what a stroke of luck. Makes me wonder if I'm the only one that when I purchase a lens and it works on all of my camera bodies the way it suppose to right out of the box.

Dietmar

Nadrek wrote:

With all due regards to Mr. Westfall, and with the very serious note
that his advice is quite good, I must state that when I did my
micro-adjustment routine, I deliberately wrote down the differences
between different ranges, and found that on most of my lenses (Canon
L's and a Sigma EX) there was a significant difference between the
"ideal" microadjustment for a "relatively close" target and a
"relatively far" target.

If you wish to spend the time on it, go through your preferred MA
routine with test targets at the closest distance you might normally
work, the average distance you normally work, and a farther distance
you might normally work (I ended up using posterboard targets - a
black and a white piece of posterboard next to each other creates a
sharp vertical line to focus on).

For zoom lenses, do that entire routine at the minimum focal length,
the middle/average used focal length, and the maximum focal length.
Yes, this means running through the test 9 times... but at best,
you'll find it was a waste of time... and you'll know that your
camera and lens is very consistent, and at worst, you'll have the
information you need to make an informed decision on what compromise
you choose you make.

The advice on selecting the "best" focal length or distance is
entirely appropriate if you only want to run the test once. If
you're willing to do it more than once, then gather more data, so you
can make a more informed decision.

My experience was that I was required to either

A) Keep an index card with different MA settings for each
lens/subject distance/focal length on it, so I could choose on the fly
or
B) Choose a compromise MA setting that allowed the nearest and the
farthest distances I could measure, at the minimum and the maximum
focal length, to be at least a little inside the DoF, and within
those constraints, I selected a MA amount that best suited the
distances+focal lengths I expect to work at.

In my case, I chose B. Unfortunately, my macro lens, at either very
long range, or at macro range, will require a noncompromising MA
adjustment - the two distances are mutually incompatible. As it's a
macro lens, I'm ok with that - macro work is its own workday, so I'll
change the MA and change it back.

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