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11-15-2013, 11:51 AM   #1
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Is sending a lens in for focus adjustment worth the time and money?

I recently acquired a Pentax K-3. Since it's a new body, I wanted to add the micro-AF adjustments for all my fast lenses to the camera's memory. I shot a quick AF test target at close to minimum focusing distance with my DA 70 under tungsten light. I decided to go with a +3 setting to correct for back focus. Well, when I went to use the camera later, shooting at a much larger distance, I found that many of the shots seem front-focused. I was worried it was due to the fact that I calibrated in tungsten but shot in daylight. But further testing in tungsten demonstrated that the lens tends to front focus at longer focusing distances, but back focus at close distances. Testing at about 6 feet versus 12 feet, the correction went from about a +2 to a -2. I guess I could split the difference and leave no correction on at all. But I feel like I'm not getting all I can out of this great lens.

So I was wondering if it would be worth the time and money to send the lens in to be calibrated. I've seen mixed reviews about this. Some saying their lens came back perfect. Others saying that the lens just gets returned from CRIS saying it was already in spec. Does anyone here have experience with sending a lens in for calibration for such an issue? Is it even possible to fix through calibration? I don't know if they have the ability to independently adjust for long and close focus.

11-15-2013, 11:58 AM   #2
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You might want to ask someone at CRIS. I suspect they'd ask you to send in both the camera and the lens.
11-15-2013, 12:09 PM   #3
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QuoteOriginally posted by devorama Quote
But further testing in tungsten demonstrated that the lens tends to front focus at longer focusing distances, but back focus at close distances. Testing at about 6 feet versus 12 feet, the correction went from about a +2 to a -2. I guess I could split the difference and leave no correction on at all. But I feel like I'm not getting all I can out of this great lens.
If you use CDAF in live view, you'll sidestep all those issues.
I'm really loving the sharpness of my Tamron 17-50/2.8 on a K-01.
11-15-2013, 12:09 PM   #4
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Similar but slightly different situation. Acquired a Sigma 8-16, that was off. Even a -10 correction was too little. I brought both camera and lens to CRIS (Sigma Warranty Center), and they realigned the lens, set it up to be perfect so as to match their optical standard. The lens was 45+ units out of calibration. They also checked it against the camera body. So, yes - to me, it was a worthwhile exercise. The lens was two days old so it was all covered by Sigma's warranty.

I would certainly give them a call and ask. I am thinking that your Pentax glass are probably out of warranty. I have no idea as to the possible cost.



11-15-2013, 12:53 PM   #5
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QuoteOriginally posted by devorama Quote
Does anyone here have experience with sending a lens in for calibration for such an issue?
Mine was the 18-135. Slightly different issue but bad enough to "initially" regret my purchase - the lens was producing images no better than cell a phone camera. I sent both the body (K5) and lens to CRIS. They calibrated the lens alone, then the body with a master lens, then finally both my lens and body together. Whatever they did made a world of difference. Focusing speed and accuracy was far better than I would hope for. As you mentioned - "the lens came back perfect"!
11-15-2013, 01:40 PM   #6
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Yes it was worth it to me. I sent in a DA21 to CRIS that required a +10 AF adjustment in the K5 but was still not good enough. $123 it came back working beautifully. They had to replace some $25 focusing part as we'll.
11-15-2013, 07:28 PM   #7
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I was new to Pentax in 2012 and bought all new lenses. Before the warranty expired, I sent a few of them in for correction and all but one came back perfect. I had to send one back a second time but now they are all good. So my experience was positive.

One of the lenses I sent in was my DA40 Ltd, for a -2 correction. In retrospect, I probably wouldn't do that again, just because of the risk in shipping something that I could so easily compensate for in my K-5, and likely in any future body I would buy.

I did speak to one guy there who mentioned some formula: something like 20x the focal length of the lens was standard procedure for setting up a focus test. Don't quote me on that. Getting back to your original question, I don't know if they have a way to independently adjust for front/back focus that varies as a function of distance. My 18-55 WR kit lens exhibits this behavior -- I did send that in for severe +10 adjustment, but I didn't even mention the variation with focus distance issue, since I just wanted to get it more in normal range, and I had much more expensive lenses to worry about.

Good luck and let us know what CRIS says if you speak to them, and how it all turns out for you.
11-16-2013, 02:51 PM   #8
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QuoteOriginally posted by K57XR Quote
Mine was the 18-135. Slightly different issue but bad enough to "initially" regret my purchase - the lens was producing images no better than cell a phone camera. I sent both the body (K5) and lens to CRIS. They calibrated the lens alone, then the body with a master lens, then finally both my lens and body together. Whatever they did made a world of difference. Focusing speed and accuracy was far better than I would hope for. As you mentioned - "the lens came back perfect"!
Same with my DA*300. I'm keeping my K-5 so I have a second body to use when I send my stuff in. Probably every year or two. Makes a huge difference when everything is tuned up. My K-5 came back from warranty repair better than new. Pentax Canada service is great.

03-29-2014, 07:19 PM   #9
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Anyone know what the going rate is for doing that for a single lens and if you get a better price if you send more than one?
03-29-2014, 08:03 PM   #10
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sent my DA*300 in a week after I got it,as was back focusing like mad..came back fine , use on K5II..Swedish Pentax service
03-30-2014, 08:54 AM   #11
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I think the OPs issue is very specifically that the focus discrepancy isn't the same at near and far distances. This completely eliminates the usefulness of the traditional tools most people use to check front/back focus. I'm not aware of anything that can be done to a lens that requires different (opposite, in this case) corrections at different distances but would be interested if anyone else has had this problem resolved.
03-30-2014, 10:05 AM   #12
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QuoteOriginally posted by tibbitts Quote
I'm not aware of anything that can be done to a lens that requires different (opposite, in this case) corrections at different distances but would be interested if anyone else has had this problem resolved.
I would say, adjust the correction for the typical distance where you want fast phase-detect focusing,
and then use the accurate (but slower) contrast-detect focusing from live view for other critical cases.
03-30-2014, 11:17 AM   #13
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QuoteOriginally posted by tibbitts Quote
I think the OPs issue is very specifically that the focus discrepancy isn't the same at near and far distances. This completely eliminates the usefulness of the traditional tools most people use to check front/back focus. I'm not aware of anything that can be done to a lens that requires different (opposite, in this case) corrections at different distances but would be interested if anyone else has had this problem resolved.
Perfectly normal and how lens work
@3ft the da70 f2.4 has 50/50 dof
@300f the da70 f2.4 has 8/92 dof

its just physics and applies to any lens

sending in wont fix , calibrating correctly will

Never ever calibrate it at MFD thats a recipe for disaster as the OP has found.

Whatever method you use the distance tool on this site will tell you how far to align and where in the DoF the peak focus should be.

LensAlign
Remember if you get it wrong the camera will be all over the place at different distances

So for the op lens

calibration should have been done at around 3.5 metres and the peak should have been set such that 48.4% in front and 51.6% behind

Setting @25xFL or 50xFL will in effect give you the comrpomise your were worried about, but its normal and what happens with all lens and bodies whoever makes them.

Last edited by awaldram; 03-30-2014 at 11:32 AM.
03-30-2014, 12:17 PM   #14
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This is all good advice. I was originally thinking it would be easiest to calibrate the lens at close to minimum focusing distance because any focus errors are easier to spot. Now I know that's not a good method.
03-30-2014, 03:16 PM   #15
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QuoteOriginally posted by awaldram Quote
Never ever calibrate it at MFD thats a recipe for disaster as the OP has found.
What is wrong with calibrating at infinity ? Works for me
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