Chuck Westfall's microadjustment tips.

Started Dec 11, 2008 | Discussions
J A K
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Chuck Westfall's microadjustment tips.
Dec 11, 2008

Below is CW's answer to the following "how to" question for the 1DmkIII; his comments/suggestions should be applicable to all models that support MA.

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What is the best way to use the Micro Focus Adjustment on the Mark III?

The question is simple enough, but the answer really depends on the lenses you're using and the way you use them. To begin with, it should be clarified that there are two types of in-camera AF microadjustment for the EOS-1Ds Mark III and EOS-1D Mark III cameras: the first adjusts the point of focus equally for all Canon EF lenses, whereas the second adjusts the point of focus for up to 20 individual lens types, at one adjustment per lens. In both cases, the point of focus can be adjusted up to + - 20 steps in 1-step increments. Also in both cases, any adjustments you make apply only to the specific camera body in question; lenses themselves are never modified by the camera's AF microadjustment settings. The amount of focus adjustment per step is proportional to the maximum aperture of the lens, with the goal being to increase the precision of the adjustment with large aperture lenses since they have a smaller depth of focus. With all that as a preamble, here is an unofficial procedure for selecting and using an AF microadjustment setting:

Mount the camera to a sturdy tripod.

Position a reference target for the camera to focus on. The reference target should have sufficient contrast for the AF system to read, should be flat and parallel to the camera's focal plane, and should be centered with respect to the picture area.

Lighting should be bright and even.

Camera-to-subject distance should be no less than 50 times the focal length of the lens. For a 50mm lens, that would be at least 2.5 meters, or approximately 8.2 feet.

Set the lens for AF and the camera for One-Shot AF, and manually select the center focusing point.

Shoot at the maximum aperture of the lens via manual mode or aperture-priority AE, and adjust the exposure level if necessary to achieve an accurate exposure of the reference target. Use a low ISO setting to reduce noise.

If the lens has an image stabilizer, shut it off.

Use a remote switch and/or the camera's self-timer to release the shutter. Use mirror lock as well.

Take three sets of images at microadjustment settings of -5, 0 and +5, i.e, three consecutive images at -5, three consecutive images at 0, and three consecutive images at +5.

Examine the resulting images on your computer monitor at 100% pixel magnification.

Take additional sets of test images at different microadjustment settings if necessary until the sharpest image is achieved.

Register the corresponding microadjustment settings in the camera.

Here are a few additional precautions to observe:

• Do not attempt to autofocus on an angled chart, because doing so will degrade the consistency of the camera's focusing measurement. Keep in mind that the camera's AF sensor is comprised of multiple pairs of linear pixel arrays. If you attempt to autofocus on a single line in an angled focusing chart, only a few pixels from each active pixel array will "see" the target. Ideally, the contrast in the reference target should cover the entire area of the camera's center focusing point, and the reference target should be perfectly parallel to the camera's focal plane.

• For best results, manually set the focus on the lens to infinity for every exposure before allowing the camera to autofocus the reference target.

• Expect some minor variations in focusing accuracy within each set of three test images, even though they were all taken at the same microadjustment setting. This is completely normal, and is due to the tolerances of the camera's AF system.

• Expect smaller microadjustment settings to have a greater effect with telephoto lenses, and vice versa for wide-angle lenses.

• If you are attempting to set microadjustments for a zoom lens, it is important to realize that the camera's setting may only be accurate for the focal length setting you test. The instruction book suggests testing at the longest focal length of the lens, but you may find it more efficient to choose the focal length you use most often.

• Some EOS cameras and some EF zoom lenses may require more sophisticated calibration than the in-camera AF microadjustment settings can provide. In such cases, it may be necessary to have calibrations performed at a Canon Factory Service Center.

• Last but not least, there is no "official" Canon method for setting AF microadjustments, so this procedure is unofficial. If you think you can do better, then by all means, go for it. Towards that end, be advised that some independently made tools are designed to help you set AF microadjustments accurately. One of these is the LensAlign kit, due out soon from RawWorkflow.com:

-----------------------------------------------------------------------------------------------------------

Regards,

Joe Kurkjian

Galleries: http://www.pbase.com/jkurkjia

SEARCHING FOR A BETTER SELF PORTRAIT

Vladyslav Kosulin
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tag (nt)
In reply to J A K, Dec 11, 2008

nt=no text.
--
Vlad

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Benedict Slotte
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My method...
In reply to J A K, Dec 11, 2008

Take three sets of images at microadjustment settings of -5, 0 and
+5, i.e, three consecutive images at -5, three consecutive images at
0, and three consecutive images at +5.

I find it better to take more, i.e. -20, -15, -10, -5, 0, 5, 10, ... That gets me to the correct result much faster, at least if the correct adjustment happens to be outside the + - 5 range.

pairs of linear pixel arrays. If you attempt to autofocus on a single
line in an angled focusing chart, only a few pixels from each active
pixel array will "see" the target. Ideally, the contrast in the
reference target should cover the entire area of the camera's center
focusing point, and the reference target should be perfectly parallel
to the camera's focal plane.

I have also found that focusing on a more "realistic" (but still plane) target is much better. Suggestion: use a flat print of an image that has much detail and contrast in it (and does NOT have repetitive patterns).

• For best results, manually set the focus on the lens to infinity
for every exposure before allowing the camera to autofocus the
reference target.

I go a step further and alternately set it to infinity and to minimum focusing distance. I don't know if that makes any difference, though.

• If you are attempting to set microadjustments for a zoom lens, it
is important to realize that the camera's setting may only be
accurate for the focal length setting you test. The instruction book
suggests testing at the longest focal length of the lens, but you may
find it more efficient to choose the focal length you use most often.

I would suggest to use the geometric mean of the minimum and maximum focal length. So, for the 100-400 mm lens, that is sqrt(100*400) = 200 mm.

• Some EOS cameras and some EF zoom lenses may require more
sophisticated calibration than the in-camera AF microadjustment
settings can provide. In such cases, it may be necessary to have
calibrations performed at a Canon Factory Service Center.

Interesting. Maybe I should try my local service center after all. They are just a 15-minute walk from my home

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B. Slotte
Turku, Finland
http://bslotte.smugmug.com

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JordanS
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Re: Chuck Westfall's microadjustment tips.
In reply to J A K, Dec 11, 2008

All excellent tips for utilizing MA. My method is to use an old license plate set about 18ft away as the target in the yard. With the target set-up a tape measure is placed at a 45 degree angle to the target extending 2ft to the rear and 2ft to the front of the plate. The resulting image clearly shows exact focus on the tape measure lines. I then set my best focus DOF to show 1/3 in front and 2/3 behind the target.

This method is very quick to detect if MA is even needed and gives latitude to set the midpoint of DOF for the shooter. This was with a 70 200 with a tc attached and different focal length lens will require a change to target distance.
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stuart melnikoff
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Re: Chuck Westfall's microadjustment tips.
In reply to JordanS, Dec 11, 2008

http://focustestchart.com/chart.html

very interesting methodology - this also seems like a worthy method but it suggests setting the target at an angle. YMMV

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WalterSrChat
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Re: Chuck Westfall's microadjustment tips.
In reply to J A K, Dec 11, 2008

Good Reference.
Thanks JAK

J A K wrote:

Below is CW's answer to the following "how to" question for the
1DmkIII; his comments/suggestions should be applicable to all models
that support MA.

-- hide signature --

What is the best way to use the Micro Focus Adjustment on the Mark
III?

The question is simple enough, but the answer really depends on the
lenses you're using and the way you use them. To begin with, it
should be clarified that there are two types of in-camera AF
microadjustment for the EOS-1Ds Mark III and EOS-1D Mark III cameras:
the first adjusts the point of focus equally for all Canon EF lenses,
whereas the second adjusts the point of focus for up to 20 individual
lens types, at one adjustment per lens. In both cases, the point of
focus can be adjusted up to + - 20 steps in 1-step increments. Also
in both cases, any adjustments you make apply only to the specific
camera body in question; lenses themselves are never modified by the
camera's AF microadjustment settings. The amount of focus adjustment
per step is proportional to the maximum aperture of the lens, with
the goal being to increase the precision of the adjustment with large
aperture lenses since they have a smaller depth of focus. With all
that as a preamble, here is an unofficial procedure for selecting and
using an AF microadjustment setting:

Mount the camera to a sturdy tripod.

Position a reference target for the camera to focus on. The reference
target should have sufficient contrast for the AF system to read,
should be flat and parallel to the camera's focal plane, and should
be centered with respect to the picture area.

Lighting should be bright and even.

Camera-to-subject distance should be no less than 50 times the focal
length of the lens. For a 50mm lens, that would be at least 2.5
meters, or approximately 8.2 feet.

Set the lens for AF and the camera for One-Shot AF, and manually
select the center focusing point.

Shoot at the maximum aperture of the lens via manual mode or
aperture-priority AE, and adjust the exposure level if necessary to
achieve an accurate exposure of the reference target. Use a low ISO
setting to reduce noise.

If the lens has an image stabilizer, shut it off.

Use a remote switch and/or the camera's self-timer to release the
shutter. Use mirror lock as well.

Take three sets of images at microadjustment settings of -5, 0 and
+5, i.e, three consecutive images at -5, three consecutive images at
0, and three consecutive images at +5.

Examine the resulting images on your computer monitor at 100% pixel
magnification.

Take additional sets of test images at different microadjustment
settings if necessary until the sharpest image is achieved.

Register the corresponding microadjustment settings in the camera.

Here are a few additional precautions to observe:

• Do not attempt to autofocus on an angled chart, because doing so
will degrade the consistency of the camera's focusing measurement.
Keep in mind that the camera's AF sensor is comprised of multiple
pairs of linear pixel arrays. If you attempt to autofocus on a single
line in an angled focusing chart, only a few pixels from each active
pixel array will "see" the target. Ideally, the contrast in the
reference target should cover the entire area of the camera's center
focusing point, and the reference target should be perfectly parallel
to the camera's focal plane.

• For best results, manually set the focus on the lens to infinity
for every exposure before allowing the camera to autofocus the
reference target.

• Expect some minor variations in focusing accuracy within each set
of three test images, even though they were all taken at the same
microadjustment setting. This is completely normal, and is due to the
tolerances of the camera's AF system.

• Expect smaller microadjustment settings to have a greater effect
with telephoto lenses, and vice versa for wide-angle lenses.

• If you are attempting to set microadjustments for a zoom lens, it
is important to realize that the camera's setting may only be
accurate for the focal length setting you test. The instruction book
suggests testing at the longest focal length of the lens, but you may
find it more efficient to choose the focal length you use most often.

• Some EOS cameras and some EF zoom lenses may require more
sophisticated calibration than the in-camera AF microadjustment
settings can provide. In such cases, it may be necessary to have
calibrations performed at a Canon Factory Service Center.

• Last but not least, there is no "official" Canon method for setting
AF microadjustments, so this procedure is unofficial. If you think
you can do better, then by all means, go for it. Towards that end, be
advised that some independently made tools are designed to help you
set AF microadjustments accurately. One of these is the LensAlign
kit, due out soon from RawWorkflow.com:

-----------------------------------------------------------------------------------------------------------

Regards,

Joe Kurkjian

Galleries: http://www.pbase.com/jkurkjia

SEARCHING FOR A BETTER SELF PORTRAIT

-- hide signature --

I am out to take the perfect picture, if it exits!

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Duane DeSieno
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Re: Chuck Westfall's microadjustment tips.
In reply to J A K, Dec 11, 2008

For me I think the important point is the 50X the focal length.
I had been fighting with my 50mm 1.4.
Close up the micro-adjust was coming out -17.
When I move 8ft away, I would get -10.
That's probably the better setting.

Also I found I can get away with not taking pictures till I'm pretty close.

Use QuickMode in LiveView and just AF-ON.

Then look at 10X in LiveView and see if the focus looks good for your favorite f stop
by using the DOF preview.

BTW all my lenses are in the the minus category. Does that mean I need to get the camera adjusted?

Duane

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click click
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tag
In reply to J A K, Dec 11, 2008

tag this message for myself

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smatty
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tag (nt) Thank you for sharing
In reply to J A K, Dec 11, 2008
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Shamus1
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Re: tag (nt) Thank you for sharing re microfocus adj
In reply to smatty, Dec 11, 2008

Methods are appreciated, will try....

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J A K
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I agree regarding using the geometric mean for zooms.
In reply to Benedict Slotte, Dec 11, 2008

Bottom line, I'm not a fan of MA; AFAIC, if you need it either your lens or body should go back to Canon for calibration (i.e. make them do the job they should have done properly in the first place).

Regards,

Joe Kurkjian

Galleries: http://www.pbase.com/jkurkjia

SEARCHING FOR A BETTER SELF PORTRAIT

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hhski
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Re: Chuck Westfall's microadjustment tips.
In reply to J A K, Dec 12, 2008

I use 3 pasta boxes the nutritional labels have heavy dark lines and the af grabs well on thisI go closer than 50x the focal length and I stagger the boxes to give me a feel if I am front or back focusing. I also notice that sometimes it is difficult to differentiate the level of sharpness but the really sharp one has the most contrast and color accuracy and saturation.The saturation is why I went to M mode to keep exposure equal.

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OleThorsen
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I prefer to measure the DOF placement
In reply to J A K, Dec 12, 2008

Thanks for sharing Joe.

Even though I use a D300, I believe the considerations should be pretty equal, since the AF adjustment has the same + -20 range. I agree about the AF target should be parallel to the sensor plane, but instead of just focusing on a flat target, I combine a flat target with a ruler placed at a 45 degree angle to the AF target, making it possible to measure the DOF placement. Here is how I adjusted my 80-400 lens, choosing the focal length and focus distance I use most for small birds.

And here is the 100% crops with the DOF placement indicated.

I ended up with a value of -8.

Regards
Ole Thorsen
http://www.pbase.com/ole_thorsen

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J A K
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Ole, your approach is a good one!
In reply to OleThorsen, Dec 12, 2008

I do almost exactly the same thing as you (i.e. get a measurement of the DOF error). Below is an example (with an enlargement of the measurement area embedded) of my 70-200 f/4 IS and 50D; note, 18 inches is aligned with the target. This is pretty much how my gear performs without any MA (I'm not a fan of MA because it isn't clear to me if the majority of AF errors are a simple offset or an offset with slope dependent on object distance).

More of what my setup looks like can be seen here. Note, I change target designs frequently to probe any weakness (false AF locks) in the camera's AF system.

http://www.pbase.com/jkurkjia/canon_30d

Also, FWIW I agree the near and far DOF limits are very symmetrical about perfect focus. Oh, another FWIW, I usually "test" for AF accuracy at a object to sensor distance of 12.2 times the focal length; this give me a magnification around -1/10 for all of the tested lenses.

Regards,

Joe Kurkjian

Galleries: http://www.pbase.com/jkurkjia

SEARCHING FOR A BETTER SELF PORTRAIT

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Robert Sheldon
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Re: Ole, your approach is a good one!
In reply to J A K, Dec 12, 2008

J A K wrote:

Also, FWIW I agree the near and far DOF limits are very symmetrical
about perfect focus. Oh, another FWIW, I usually "test" for AF
accuracy at a object to sensor distance of 12.2 times the focal
length; this give me a magnification around -1/10 for all of the
tested lenses.

Regards,

Joe Kurkjian

Joe,

Only an engineer would use 12.2. Ordinary slobs would use 12 or more likely 10 or 15.
--
Bob Sheldon
Photo Gallery at
http://www.bobsheldon.com

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Sunghwa Jin
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nt means no text.

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NumberOne
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(NT) Thank you very much for posting - Chuck Westfall's microadjustment tips.
In reply to J A K, Dec 12, 2008

Best regards,
Pedro

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Eric Hoffman
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Eric

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kipryan
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Re: Tag
In reply to Eric Hoffman, Dec 12, 2008

Bookmarked

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jrsforums
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Another approach
In reply to Eric Hoffman, Dec 12, 2008

I have not tried it...yet (waiting for 5D2)

http://www.northlight-images.co.uk/article_pages/cameras/1ds3_af_micoadjustment.html

But this seems like a good method...

John

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