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03-01-2010, 07:51 AM   #1
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Join Date: Jun 2007
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AF Adjustment for K20D

I would like to seek helps of how to do a proper AF Adjustment for my lens on K20D. The manual does not explain much in details, I think I have screwed up some how while trying on one of my lens.

I have the following:-

1) Tamron 17-50mm, F2.8
2) Tamron 18-250mm, F3.5-F6.5
3) Pentax DA* 50-135mm, F2.8 (though this lens still works pretty well with the camera).

Thank you in advance.

03-01-2010, 10:22 AM   #2
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Join Date: Oct 2007
Location: Port Townsend, Washington State, USA
Posts: 3,659
mklai,
I've only done it twice, but i'll put down my observations:

1. You want the most shallow DOF for that lens so the adjustments are readily discernable. so if a lens is max F2.8 aperture, have it in that aperture.

2. Its best to do the adjustment on a tripod for greatest precision. But i used the adjustment on the fly during a play dress rehearsal when i noticed that the tungsten light seemed to be causing my lens to front focus, e.g. the jacket in front of the face was sharp but not the face. I quickly dialed in a minus 4 or 5 micro inches and problem was fixed.

3. AF adjustment is Line 35 of the menu. To see if there is an existing adjustment on a specific lens, go to the Adjust one menu, and if its not at zero, you have an existing adjustment for that lens. on the adjust all lens, same thing, if it shows an existing adjustment, it means all the lenses are subject to that adjustment.

4. You can adjust using the left right of the 4 way wheel, or the rear e-wheel. Plus adjustments to the right of zero, adjust the focus of the lens farther to subject front. Minus adjustments to the left of zero, adjust the focus farther behind the subject.

5. Someone has suggested using some playing cards You set in front of the camera. The closer to the camera, the shallower the DOF. However, you might want to set the cards at a more generally used distance to replicate that situation, as some lens adjustments can vary with distance (reportedly). One card is set horizontal in front of the lens, one is angled closer to the camera and another is angled farther away from the camera. When adjusting the focus, one should be able to see the focus shift from the middle card farther to the front and/or farther to the away card.

6. I would suggest you just work with your most used lens to get that right before making any wholesale lens adjustments to all. If you find that all 3 of your lenses need adjustment in the same direction, then one "all" adjustment might be appriopriate.

7. I've read that hitting the green button while in the adjustment mode resets the adjustment to the zero value.

8. You can't hurt your lens or camera using this adjustment process, so just play with it awhile and i'm sure you'll get the hang of it.

Best wishes
03-01-2010, 02:29 PM   #3
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Join Date: Sep 2006
Location: Tartu, Estonia
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There might be a problem with non-Pentax glass: as the lens IDs used by 3rd party glass are not genuine for Pentax camera the adjustments MAY overlap. E.g. my Sigma 24-135 and Tammy 18-250 share something similar so I can not adjust them individually- adjust one and when I switch then false adjustments are applied - at least on my K20D. With Pentax branded glass everyone has its unique adjustments.
One remark though- after perfect adjustment in daylight You must know that in artificial light Your lenses will front-focus a tad- but it is easily correctable when You do an extensive shooting in different conditions- just readjust before...
Best and happy adjusting, JR
03-07-2010, 09:04 PM   #4
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I love the search function- this is exactly what I need to know. I believe that my Tamron 17-50 may be just slightly front-focusing. I have seen someone post a technique using a ruler somewhere, as well.

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