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05-20-2019, 05:22 AM   #1
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Odd repair on my DFA 24-70mm

I just got my DFA 24-70 back from the repairer in Germany for back focus, they had it and the camera for almost four weeks.

I had previously sent this to them for decentering about 9 months ago (you might be able to see the old thread), and hadn't properly tested it since I got it back. Just when I got my k1 upgrade did I realise that it was back-focusing at the equivalent of about -15, beyond what was fixable in-camera.

Anyhow, they repaired it for a reasonable price, around 80s. but, when I got it back and checked the focus on my Spyder LensCal, I see that it still needs adjustment of about the max - 10. So it's okay I guess, but pretty poor showing really.

Anyhow, I'm wondering how difficult it can be to adjust a lens so that it focuses without needing AF adjust, given that the technician adjusted the lens and they had the camera to test it with. Surely this would be just standard practice in this case - at least get it +- 3? Seems like a pretty slack repair job.

05-20-2019, 05:30 AM   #2
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QuoteOriginally posted by dofmaster Quote
I just got my DFA 24-70 back from the repairer in Germany for back focus, they had it and the camera for almost four weeks.

I had previously sent this to them for decentering about 9 months ago (you might be able to see the old thread), and hadn't properly tested it since I got it back. Just when I got my k1 upgrade did I realise that it was back-focusing at the equivalent of about -15, beyond what was fixable in-camera.

Anyhow, they repaired it for a reasonable price, around 80s. but, when I got it back and checked the focus on my Spyder LensCal, I see that it still needs adjustment of about the max - 10. So it's okay I guess, but pretty poor showing really.

Anyhow, I'm wondering how difficult it can be to adjust a lens so that it focuses without needing AF adjust, given that the technician adjusted the lens and they had the camera to test it with. Surely this would be just standard practice in this case - at least get it +- 3? Seems like a pretty slack repair job.
How much if any do your other lenses require in the way of AF/FA ?

The reason I ask is that Pentax will adjust any camera that requires adjustment in excess of -10/+10 for free.

I had always considered the adjustment to be to the camera and not the lens.
05-20-2019, 05:56 AM   #3
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QuoteOriginally posted by dofmaster Quote
Surely this would be just standard practice in this case - at least get it +- 3? Seems like a pretty slack repair job.
You are confident that your body is perfectly adjusted then?
05-20-2019, 07:11 AM   #4
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QuoteOriginally posted by pschlute Quote
I had always considered the adjustment to be to the camera and not the lens.
Me too. I understand the adjuster is under the bottom plate.

05-20-2019, 07:13 AM   #5
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Sometimes it's the body that's completely out of spec. My first K1-II required AF adjustments for all of my lenses beyond what was reasonable. It was subsequently exchanged for a different body that required zero adjustment. This was confirmed using a standard focus test target at 45 degree angle with the camera on a tripod under even lighting.

05-20-2019, 07:50 AM   #6
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My other DFA lenses that I have tested (a 70-200 and the 50) are all within tolerance, maybe around -3 to -5.

My 24-70 was three weeks out of warranty when I took it to the shop.

The camera was recently upgraded as k1m2, so still under the temp warranty. According the repair notes the adjustment was made to the lens.

I couldn't get a proper explanation out of the shop about what the Ricoh servicer did because the person who initially processed my issue was away on holiday when I picked up my camera.
05-20-2019, 09:14 AM   #7
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QuoteOriginally posted by dofmaster Quote
My other DFA lenses that I have tested (a 70-200 and the 50) are all within tolerance, maybe around -3 to -5.
Hmm, then all of the lenses are now within 7 points...the fact that all of them are backfocusing suggests that the camera is part of the problem. If the body was adjusted by -5 then all lenses would be within +/-5
05-20-2019, 09:26 AM   #8
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If the faulty lens was -15, and now it's about -10, and that's just because they adjusted the camera sensor position or AF module or whatever, then my other lenses if they are around -5 now would have previously been -10, which they weren't.

I don't know how many of you have checked your Pentax zoom lenses AF in minute detail, but I can tell you it ain't always pretty. Long and short ends often don't match, even if they are in the range, but tend to be out by at least +/- 1 or 2.. But maybe this is normal for camera lenses, I'm not an expert.

per se it's not a problem, since it's adjustable within the camera, it's just a sloppy repair job that doesn't exactly inspire confidence. This is the second time the lens has been in for a problem, but I can't prove a connection.

05-20-2019, 09:38 AM   #9
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QuoteOriginally posted by dofmaster Quote
Anyhow, they repaired it for a reasonable price, around €80s. but, when I got it back and checked the focus on my Spyder LensCal, I see that it still needs adjustment of about the max - 10. So it's okay I guess, but pretty poor showing really.
How is the lens in the field?

QuoteOriginally posted by dofmaster Quote
I don't know how many of you have checked your Pentax zoom lenses AF in minute detail, but I can tell you it ain't always pretty. Long and short ends often don't match, even if they are in the range, but tend to be out by at least +/- 1 or 2.. But maybe this is normal for camera lenses, I'm not an expert.
An amazing number of users on this site are incredibly into this sort of thing. As for different settings at the long vs. short, that is not unusual regardless of brand* and it usually requires a service visit to put right.

QuoteOriginally posted by dofmaster Quote
per se it's not a problem, since it's adjustable within the camera, it's just a sloppy repair job that doesn't exactly inspire confidence. This is the second time the lens has been in for a problem, but I can't prove a connection.
Your issue is with the shop. Standard advice here is to ask them to take it back with them paying the shipping both directions.


Steve

* Example: Fine adjustment of a Sigma using their "dock" device often requires tweaks at multiple focal lengths and multiple focus distances.
05-20-2019, 09:57 AM   #10
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QuoteOriginally posted by pschlute Quote
I had always considered the adjustment to be to the camera and not the lens.
Usually, it is the lens, though camera can be at fault too. Problems on the camera might include:
  • Improper image sensor position (surface not at expected focal plane)
  • Improper PDAF sensor position (alignment and/or not same optical distance as the image sensor)
  • Bad primary or secondary mirror alignment
  • Soiled mirror or PDAF sensor lens
  • Mechanical issues in AF pawl drive
On the lens side:
  • Decentered or improperly positioned element(s)
  • Improper spacing of floating elements used for zoom/internal focus
  • General optical defect making focus ineffective overall
  • Mechanical issues with internal focus drive including physical damage
The lens is usually the problem unless a general tendency where all lenses show a focus bias front or back with little or no mix between the two.


Steve
05-20-2019, 10:10 AM   #11
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QuoteOriginally posted by stevebrot Quote
The lens is usually the problem unless a general tendency where all lenses show a focus bias front or back with little or no mix between the two
I can only be guided by my own experience where all my lenses require between +6-+9 adjustment on my K1
05-20-2019, 11:54 AM   #12
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QuoteOriginally posted by pschlute Quote
I can only be guided by my own experience where all my lenses require between +6-+9 adjustment on my K1
It's one thing to be able to correct all your lenses, it's another thing knowing you can't quite get the maximum sharpness on a zoom because the adjustment is out at different parts of the zoom range.

---------- Post added 05-20-19 at 11:57 AM ----------

QuoteOriginally posted by stevebrot Quote
How is the lens in the field?



An amazing number of users on this site are incredibly into this sort of thing. As for different settings at the long vs. short, that is not unusual regardless of brand* and it usually requires a service visit to put right.



Your issue is with the shop. Standard advice here is to ask them to take it back with them paying the shipping both directions.


Steve

* Example: Fine adjustment of a Sigma using their "dock" device often requires tweaks at multiple focal lengths and multiple focus distances.
It's okay, but I haven't used it a lot, so I can't say exactly. using for an event tomorrow.

As for asking them to refix - I'm not sure - if it's +10 is it still legitimately a problem? I also do not want to send my camera away for another 2-4 weeks. Lens I'm find to send away though.

---------- Post added 05-20-19 at 11:58 AM ----------

QuoteOriginally posted by stevebrot Quote
Usually, it is the lens, though camera can be at fault too. Problems on the camera might include:
  • Improper image sensor position (surface not at expected focal plane)
  • Improper PDAF sensor position (alignment and/or not same optical distance as the image sensor)
  • Bad primary or secondary mirror alignment
  • Soiled mirror or PDAF sensor lens
  • Mechanical issues in AF pawl drive
On the lens side:
  • Decentered or improperly positioned element(s)
  • Improper spacing of floating elements used for zoom/internal focus
  • General optical defect making focus ineffective overall
  • Mechanical issues with internal focus drive including physical damage
The lens is usually the problem unless a general tendency where all lenses show a focus bias front or back with little or no mix between the two.


Steve
They said they checked the camera, and it's a newly upgraded K1M2, so i have to take their word for it.

This was the 3rd time the lens went in total in its 2.2 year life, the second time for bad decentering (the first time for an unresolved AF underperformance/lack of sharpness issue).
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