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01-22-2012, 08:57 AM   #1
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AF lens calibration help

I finally decided to check the AF calibration of my K-5 with the 3 AF lenses I currently own, starting with the kit 18-55 WR. Can someone point me to a basic guide how I should approach this for the K-5? I already printed out a test chart from Jeffrey Friedl's Blog on good photographic paper, and I have a rough idea what to do; shoot the chart at 45 degree angle at wide-open aperture. I shot a few images, but I'm really unsure how to proceed. Also, are there any camera settings that I need to be concerned with when shooting the test chart other than aperture?

I did a quick site search and did not come up with answers.

01-22-2012, 10:27 AM   #2
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First set the camera to use only the center focus point.

The chart you are using may not be the best for the job. To be sure, try to use Live View and focus on the center focus line. Focus MUST be perfect in LV, if not that the chart does not have enough contract in the focus area or has too many competing elements around it. Remember that the focus point is not a point actually; it is a small area. If your focusing plane is tilted, then all the elements within the focus area are used and focus could be anywhere.

A better approach is to use a focus chart that is parallel to the sensor (the lens point to it at 90 degrees) and next to it to have a ruler (or the chart you are using) at 45 degrees with the "focus" line intersecting the focus chart. That way the focus system uses the vertical chart (everything in the same distance so does not matter how much of it is used) and you use the 45 degrees chart to see where actually achieved best focus.

Then adjust the camera to correct for front/back until you get an image when both the vertical card is in perfect focus and the DOF on the ruler is more or less equally distributed from the center focus line.
01-23-2012, 02:19 AM   #3
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I'll give LV a try and I've also ordered the Spyder LensCal kit, which should provide a much better test target.

With a zoom, how to deal with multiple focal lengths? I know I can apply only one calibration factor per lens, but what is the best focal length to use for a zoom?
01-23-2012, 09:29 PM   #4
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You'll have to live with the fact that zooms often require different AF adjustment settings depending on focal length and/or subject distance.

You may want to check out my AF adjustment hints.

05-20-2012, 10:46 PM   #5
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I found a pretty cool technique I am going to try which uses the contrast AF of the Live view to help calibrate the phase detect AF system. Read below.
autofocus - What is the best way to micro-adjust a lens? - Photography
05-22-2012, 12:13 PM   #6
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QuoteOriginally posted by Tonto Quote
I found a pretty cool technique I am going to try which uses the contrast AF of the Live view to help calibrate the phase detect AF system. Read below.
autofocus - What is the best way to micro-adjust a lens? - Photography
That sounds like an interesting way to calibrate AF, will have to give it a try.
05-23-2012, 12:31 AM   #7
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QuoteOriginally posted by cbope Quote
That sounds like an interesting way to calibrate AF, will have to give it a try.
I use a manual focusing live view method, this uses a test target on an LCD screen

AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D

It is this method which give's me hope of an automatic process being possible for a new camera.

Last edited by Col; 05-23-2012 at 08:03 AM.
05-23-2012, 07:08 AM   #8
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QuoteOriginally posted by Tonto Quote
I found a pretty cool technique I am going to try which uses the contrast AF of the Live view to help calibrate the phase detect AF system.
That's a convenient approach for sure, but it has the limitation that the contrast AF's precision is not as high as it should be to allow for an optimal phase AF setting.

This method should get the AF adjustment in the right ballpark, but if you want utmost precision, you should do a focus series with varying AF adjustments (multiple shots for each setting as well).

This kind of precision may not be warranted for normal usage, but I think it is good to be aware of the fact that contrast AF has its own tolerances and does not define the be all and end all of focusing accuracy.

01-29-2014, 10:20 PM   #9
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I've put my LensAlign MkII Focus Calibration System up for loan. Head on over to read the details.
01-29-2014, 11:24 PM   #10
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I shoot the edge of my cement walkway centered on the crack with the short grass. Very easy to see the focus zone.
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