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12-01-2012, 08:07 PM   #1
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Focus Chart Calibration - User error or camera problem?

Ok, I've been trying to dial in my lenses on my K30 and noticed some things that I'm unsure about. I've followed the instructions and set the chart up, camera angle is correct, as is the distance. The first part of the test is to focus the camera at the white half of the oval to confirm that the camera cannot lock focus. I noticed that there were times with all my lenses where my camera would lock focus on an all white object despite the entire centre ( ) being well inside the white area.

The camera is set to Av, no SR on, centre point only and spot metering using a 2 second timer on my tripod.

I know that the focus points are larger than the centre red dot but surely not larger than the full centre circle. Is this abnormal? Is it camera error or user error? Most of my lenses seem to need a large focus correction (+10 isn't enough for the 24-70 and the 50-150 is very different at each end of the range - ie strong front focus towards 150mm and back focus towards the 50mm end).

It makes me curious if the alignment of the focus points is correct. I'm certainly not rulling out user error though.

Thoughts?

12-01-2012, 08:46 PM   #2
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Hi, focus adjustment can be a bit of a black art. My recent lenses I seem to have got right so thats progress...

Not sure which charts you use but I use charts as seen on: PENTAX DSLRs: Front or Back Focusing Problems? Free test (Lens Alignment) charts for Pentax, Nikon, Canon, Sony, Olympus.

These charts come in several sizes and I have found it is important to use the right size one for the focal length you are using (in order to get a good size focus target at a consistent focus distance). It may be that the target on focus chart you have, is too small for the focal lengths / focus distance you are tuning at?
12-01-2012, 08:57 PM   #3
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Those are the charts I'm using. I've been testing with the medium sized chart. The camera is positioned such that the entire ( ) is never larger than the focus circle. With that ( ) entirely within the white portion of the circle I can often get the camera to lock focus. That seemed odd to me.
12-01-2012, 09:11 PM   #4
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Check your lighting, if it is not quite bright enough there will still be some contrast.

Also, what kind of paper did you print them on? Plain copy or printer paper has plenty of contrast in it. Hi quality white photo paper works better for me.

12-02-2012, 05:56 AM - 1 Like   #5
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I don't use charts at all. I use the method described here: AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D, 1D X

I don't have a K30, but I assume it has liveview.
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