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10-21-2010, 07:21 AM   #1
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Pentax K-r -- acceptable focus adjust for a new body?

I finally had an evening to seriously look at my new K-r that I picked up at the Photo Show on Saturday. I am really liking this camera ... not perfect, but really good.

I had suspected I wasn't seeing the full sharpness of the K-r, but I haven't pixel peeped at all. Mostly just chimping the back of the camera. So last night I methodically put the K-r through the paces alongside my K20D, mounting each of my most-used lenses. I shot a series of test shots, closeups, mid distance and long (about 25 feet) distance. I haven't checked infinity.

I double checked the AF fine tuning that I use for the K20D. Those numbers are:
  • Pentax FA 77/1.8 (+- 0 lens adjust, +- 0 body adjust)
  • Pentax DA 35/2.4 (yes the new one!) (+- 0 lens adjust, +- 0 body adjust)
  • Sigma 24-135/2.8-4 (+ 4 lens adjust, +- 0 body adjust)
  • Sigma 28-70/2.8 EX DG (+ 4 lens adjust, +- 0 body adjust)

The K-r has AF fine tuning, but one setting only (unlike the K20D which allows a universal plus memorizes individual lenses.)

Setting up the K-r to focus as well as the K20D required:
  • Pentax FA 77/1.8 (-9 adjust)
  • Pentax DA 35/2.4 (-9 adjust)
  • Sigma 24-135/2.8-4 (-5 adjust)
  • Sigma 28-70/2.8 EX DG (-5 adjust)

My concern is... should I have to enter such serious front focus correction on a new body for Pentax-branded lenses? This K-r in stock configuration is clearly front-focussing. Yes, I can adjust it into sharpness. But is this within tolerances?

My K10D was also off, especially with the Sigma glass (which I really like.) Not being able to fine tune AF was the major reason I moved to the K20D. With the K20D, the Pentax glass seems great -- factory tolerances on both the bodies and lenses line up. Having to tweak the Sigmas is no surprise, but I am glad I can do so.

My concern is that the K-r is 9 points off the K20D. There are only 10 steps of correction! If my FA 77 and DA 35 are "factory correct" and match my K20D, then I am tempted to think of them as closer to the "norm." What if I buy another lens (even a Pentax Limited) and it's out just a bit in the other direction? Say, requiring -3 adjust on the K20D? Then ... I'll never be able to get it properly set on the K-r.

One further wrinkle, is that I want to recheck all my testing with good daylight. I am suspicious about AF performance under different wavelengths of light. And most important to me is AF accuracy in daylight.

So.... sanity check time. Should I return the K-r and get another body? Am I being too picky, and this if within spec? Should I be happy because I was wise and bought the K-r because it has AF fine tune? Or should I be unhappy because I need to adjust it to -9 with good Pentax glass?


Last edited by filmamigo; 10-21-2010 at 11:46 AM.
10-21-2010, 09:01 AM   #2
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So, the K-r doesn't memorize AD adjustments for individual lenses--which means that you have to make the adjustment every time you mount a lens?

Now, to answer your question, the sensible answer is: return the K-r and ask for an exchange. Clearly, a good body shouldn't require such enormous corrections.
10-21-2010, 09:16 AM   #3
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Return it and get a K5.
10-21-2010, 11:46 AM   #4
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causey:

Yes, but it's not as onerous as it sounds. It's a global adjustment and it's memorized. So, for example, nothing changes if I switch between the DA 35 and FA 77. Yes, I have to change it for another lens with a different value. It's quick to do, almost as fast as changing the JPG compression level or the metering mode on the K-r.

It's much better than the situation a couple of years ago, where the only option was to engage in a round-robin of lens returns or trips to the manufacturer for tweaking.

telfish: You're not helping here! The K-r was my solution to keep from spending the money on a K-5...

10-26-2010, 02:10 PM   #5
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I did quite a bit more testing ... and found that the front focusing was better (i.e. less bad) under daylight conditions. But still not perfect. For example my FA 77 was sharpest at -5 adjust.

Which pushed me towards returning the K-r for another body, which I did. I wanted to make sure I got one I was happy with, inside of the 14 days I have to make up my mind. So... I took the K-r back and after much consideration, I ordered a K-5.
10-26-2010, 02:20 PM   #6
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It's ok filamigo, my K-r needs -9 adjustment too.
10-26-2010, 03:33 PM   #7
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Yes, tungsten lighting will cause front focus on all but K-7/5
10-26-2010, 03:44 PM   #8
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QuoteOriginally posted by filmamigo Quote
I methodically put the K-r through the paces
What is your AF testing methodology, out of curiosity? AF testing is hard to do right.

10-26-2010, 04:35 PM - 1 Like   #9
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Everyone should do the the moire interference test:
AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D
Using Moire' Interference Patterns to Test DSLR Auto Focus

Most accurate, can do indoors without worrying about tungsten, easier to line up 100% perpendicular yet less affected by it compared to a focus chart.

Last edited by Eruditass; 10-26-2010 at 05:14 PM.
10-26-2010, 05:15 PM   #10
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My most rigorous test, done inside (tungsten) and outside (daylight), is to place a contrasty object on the ground beside an extended tape measure. Camera on a tripod about 6 feet away. Turn SR off. Aperture priority to wide open. Defocus the lens, then AF on the contrasty object. Shoot. Eject the card and pop it in a laptop. Check the results at 100%, and see where the band of focus actually lies. Adjust AF Fine Tune, rinse, repeat! This admittedly crude regimen, when done carefully, has proven effective with my K20D.

I double check against this, before and after, through a bunch of "common sense" shooting. I try not to punish the AF system, so I test in good light. I shoot contrasty objects at a range of distances (say 12 inches, 3 feet, 8 feet, 20 feet, 50 feet) to confirm that the adjustment yields good results at a range of distances and zooms. Some things outside make great impromptu focus checkers, like picket fences or light fixtures on brick walls.... when examining the results at 100%, the materials surrounding your target make it easy to see where your critical focus line really landed.

I understand that I could be WAY more methodical about this. But I honestly don't want to be running an optical test bench and collimating lenses. (Though I have done that on some restored vintage folding cameras!)

The good news here is that the K-r has AF Fine Tuning. I could get pin-sharp results from all of my lenses. This is a great improvement over the K10D and many (most?) of the cameras from other camera manufacturers.
10-26-2010, 05:21 PM   #11
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QuoteOriginally posted by Eruditass Quote
Everyone should do the the moire interference test:
AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D
Using Moire' Interference Patterns to Test DSLR Auto Focus

Most accurate, can do indoors without worrying about tungsten, easier to line up 100% perpendicular yet less affected by it compared to a focus chart.
Cool! Thanks for the link! I've bookmarked it.
10-26-2010, 05:21 PM   #12
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QuoteOriginally posted by arm_jstp Quote
It's ok filamigo, my K-r needs -9 adjustment too.
Interesting... thanks.
10-26-2010, 05:23 PM   #13
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QuoteOriginally posted by Eruditass Quote
Yes, tungsten lighting will cause front focus on all but K-7/5
Does this anomally occur on other brands/models too? Is Pentax a leader or a follower in providing AF that is corrected for light wavelength?
10-26-2010, 05:41 PM   #14
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Could someone explain me the problem?
I'm saving for a K-R and I currently have a K100D Super.

Thank you,
Yael
10-26-2010, 06:07 PM   #15
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YJD, you will love the K-r.

For a longer description of front focus/back focus (an issue that can happen to a particular copy of ANY camera) see my other thread: https://www.pentaxforums.com/forums/pentax-dslr-discussion/119902-k-r-so-good-im-trading.html
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