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03-05-2012, 10:50 AM   #1
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best procedure to adjust auto focus?

I did a search on this topic but I don't see something like a knowledge base article that lays out a best methodology to tweak the K-r's auto focus. Is there one that could be added to the how-to article section?

Page 128 of the manual lays out how to use the menu control, but there is no information beyond 'take a test picture' about the best way to use this tool. It seems a number of people have tweaked their auto focus, so rather than forcing us to 'reinvent the wheel', what have you found as the best and fastest way to get the job done?

03-05-2012, 11:38 AM   #2
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Here it is:
Fixing Front and Back Focus - Introduction - PentaxForums.com

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03-05-2012, 02:42 PM   #3
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It might help reading this thread too.
https://www.pentaxforums.com/forums/pentax-k-5-forum/177572-all-fuss-about-au...oint-size.html
03-05-2012, 03:03 PM   #4
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I have a K2000 and a Kr, the K2000 never focused to my satisfaction but the Kr was close. I tried focus charts but that never worked for me. Both the K2000 and the Kr have a image comparison screen where you can compare 2 images at the same time on your camera monitor. I just shot an image of a car license plate (at a distance) with 0 focus compensation then one with +1 and compared the 2. if +1 was better i tried the same with comparing +1 & +2 if not i tried 0 and -1 until I got the best image. My Kr needed +3 and my K2000 needed +16 (using debug mode) I am now happy with both and actually use my K2000. After I got the Kr I would not even think of using the K2000 until i fixed the focus.

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03-05-2012, 04:41 PM   #5
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There was another method that someone else talked about on one of these forums, but I can't seem to find it.

Basically they suggest using Live View to Autofocus (which uses contrast detection), mark the focus ring and the lens so that the marks line up then use the viewfinder focus (phase detection) and see if the lines meet. If they are off, dial in some adjustment and repeat. I've never tried it but is sounds like it might work.

Not sure about marking the lens but a small piece of tape might work the same.

AB
03-06-2012, 07:11 AM   #6
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Yes I have also used live view but then used the in camera image comparison to determine the best AF compensation. This only worked on my Kr as my Km doesn't have LV and assumes that live view is perfect.

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03-06-2012, 08:28 AM   #7
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QuoteOriginally posted by ablundon Quote
There was another method that someone else talked about on one of these forums, but I can't seem to find it.

Basically they suggest using Live View to Autofocus (which uses contrast detection), mark the focus ring and the lens so that the marks line up then use the viewfinder focus (phase detection) and see if the lines meet. If they are off, dial in some adjustment and repeat. I've never tried it but is sounds like it might work.

Not sure about marking the lens but a small piece of tape might work the same.

AB
I have used the technique mentioned in this link: AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D and it works quite nicely. I am sure live view focus can be off, but it is much less likely than having normal autofocus inaccuracy since focusing is done at sensor level.
03-07-2012, 08:16 AM   #8
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QuoteOriginally posted by Adam Quote
The problem with this review is it recommends purchasing a relatively expensive tool, while it appears to be excellent, amounts to a surcharge on the purchase price of the K-r. I shouldn't have to spend this much money to get more accurate focus with a K-r using the kit DA L18-55mm lens.

So, I started digging further and found this excellent - and currently free (other than the cost of printing a sheet of paper) option:
PENTAX DSLRs: Front or Back Focusing Problems? Free test (Lens Alignment) charts for Pentax, Nikon, Canon, Sony, Olympus.

Yvon Bourque has an excellent step by step instruction. It actually took me longer to read his instructions than it took me to tweak my camera's auto-focus. His instructions specifically reference the K-5, but other than the menu position and reduced function set of the K-r, the instructions will be the same.

I used the kit 18-55 lens at roughly 28mm, Av with the maximum possible aperture (f/4.0), turned off Shake Reduction, set center spot focusing and placed the camera about a foot (30cm) from and level with the scale. I had adequate ambient light and didn't even bother with a tripod - I am sure I could get even better results if I had used a tripod, but I was at this point just experimenting to see if I understood the instructions. The target told me I was auto-focusing about 4mm to the front of my ideal focus point.

After a little playing, I figured out that the scale in the AF Fine Adjustment menu roughly corresponds to millimeters. and that you move the AF Fine Adjustment in the menu to the minus side for front focus elimination and to the plus side for back focus elimination. I currently have my camera's AF Fine Adjustment set to -4. Indeed, my test shots show better focus where I expected it to be.

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