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08-14-2022, 03:40 AM   #1
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DA☆11-18mm F2.8 focusing accuracy

Anyone owning the Pentax DA☆11-18mm F2.8, was your lens sharp right out-of-the-box or did you need to use the AF fine adjustment or even send it for repairs/replacement?

I recently bought one and out-of-the-box it tended to focus closer than it was supposed to be (tested it on two different K-3 bodies). Managed to get decent performance when pushing the AF fine adjustment in camera up to 10, but that did not sit well with me, as there was no durther room for adjustment. Took it back to the store and they sent it to European center for repairs. It now returned, but the focus still seems to be off (now it tends to focus too far) and I can't even get consistent results with the AF fine adjustment - at some point -10 seems to do the trick, then +3, then 0 again etc...

Has anyone experienced something similar with this lens or any other Pentax lens? Seems odd for a star-series lens to perform like this.

08-14-2022, 03:50 AM   #2
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I have one and it performs well on my K-3 Mark II and my KP (even better) very sharp perfect rendering of colours, no adjustment necessary. What does the repair report say they did to adjust focusing?
08-14-2022, 04:13 AM   #3
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I havenít noticed this issue but Iím less critical of focus than some people. Is the problem there when you use live view? If it is then af fine adjustment arenít going to help. With a very wide angle lens the focus typically is pretty deep and accurate focus is usually easy. Some people have had to send their body and lens together to get good focus accuracy for tricky lenses - but existing lenses could need to be setup again to compensate if changes are made to match the new lens that affect global focus accuracy.

To be completely fair Iíve mostly used mine on my KP. Iím sorry I canít test it on my k-3 as Iím out of town and donít have it with me.
08-14-2022, 04:14 AM   #4
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QuoteOriginally posted by rRnt Quote
Has anyone experienced something similar with this lens or any other Pentax lens? Seems odd for a star-series lens to perform like this.
Your lens may have a defect, it's possible. However, after doing a lot of AF precision and accuracy measurements, I found that the Pentax factory calibration is a pretty good compromise for minimum focus distance to infinity and from the minimum focal length to the maximum focal length.

When people look at AF accuracy, they usually use one subject at one distance using one focal length at one aperture value and also ignore the precision impact on accuracy from run to run. Consequently, they may set +10 AF fine correct for a subject at 2 meters distance, and actually worsen the AF accuracy at infinity and at apertures values different from the one used for AF fine tuning. In some cases, AF fine tune other than 0 is dialed in for one lens setting/subject distance, making the overall AF accuracy worse for all shooting conditions.

08-14-2022, 04:20 AM   #5
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Based on my observations, I have only two lenses with AF fine tuning -2 and +3, as a result of performing multiple AF error measurements at different focal length and focus distance, and averaging those errors. For all my other lenses, multiple measurements showed that the Pentax factory calibration was optimal, so I don't have any AF fine adjustment dialed in for those lenses.
08-14-2022, 04:37 AM   #6
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QuoteOriginally posted by rRnt Quote
I can't even get consistent results with the AF fine adjustment - at some point -10 seems to do the trick, then +3, then 0 again etc...
Sounds strange because if AF was inconsistent you would never be able to tell/confirm that -10 (or +3, or 0) seems to do the trick. Inconsistent AF means would never be able to find any suitable AF fine adjust value. What method do you use to determine the AF fine adjustment value?
08-14-2022, 04:38 AM - 1 Like   #7
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Unlike most of the other new lenses, there has been no specific firmware update for the 11-18 with the K-3 to optimize focus. Check which firmware version you are currently running, as the latest one (V1.43) could perhaps be a benefit. Good luck.

Latest K-3 Firmware Update : Software Downloads | RICOH IMAGING

08-14-2022, 05:11 AM   #8
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well ...

Update the firmware and then try this again ...


My first copy of DA* 11-18 had a similar issue. The only precise AF point was the center AF point. All corner AF points required corrections - when shooting almost close-up photos, all of them were 10cm out of focus. Thus the lens had a curved focus plane and this could (?) be corrected in the official Ricoh service. At least I would expect that they can do that.


So I had returned that copy of DA* 11-18 within the two weeks period and got another copy not having this issue.
08-14-2022, 08:26 AM   #9
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Lens or camera is off if you see experience a consistent offset outside the range. Pentax can zero the effect. Make sure all your other lenses work afterwards - the lens should be matched to the camera and vice versa. Pentax typically asks you to send in all your lenses. Depending on where you life, this is done free of charge as long as the warranty is valid.
08-14-2022, 09:48 AM   #10
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QuoteOriginally posted by biz-engineer Quote
Sounds strange because if AF was inconsistent you would never be able to tell/confirm that -10 (or +3, or 0) seems to do the trick. Inconsistent AF means would never be able to find any suitable AF fine adjust value. What method do you use to determine the AF fine adjustment value?
Zooms often need differing adjustments at different focal lengths. I tend to try to set them in a place that gives best across multiple focal lengths but I also tend to stay with factory af adjustment unless itís really bad.
08-14-2022, 11:47 AM   #11
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Thanks for all the answers so far.

Camera firmwares are updated, I aquired a second K-3 body two months ago and upgraded them both.

I hope the retailer is able to provide some documentation about what was done with the lens at the maintenance center, they certainly did not include any report when they handed the lens back to me. I also need to try out different zoom, aperture settings and focal distances systematically. I have tried it in different scenarios (close and far objects), but it is difficult to make any accurate conclusions when the exif does not display the AF adjustment data.

I have never experienced problems like that before with my lenses, I was hoping the Star-series had better quality control.
08-14-2022, 12:07 PM   #12
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QuoteOriginally posted by UncleVanya Quote
Zooms often need differing adjustments at different focal lengths. I tend to try to set them in a place that gives best across multiple focal lengths but I also tend to stay with factory af adjustment unless itís really bad.
this is more about the focus plane curvature.
08-14-2022, 01:04 PM   #13
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QuoteOriginally posted by rRnt Quote
Thanks for all the answers so far.

Camera firmwares are updated, I aquired a second K-3 body two months ago and upgraded them both.

I hope the retailer is able to provide some documentation about what was done with the lens at the maintenance center, they certainly did not include any report when they handed the lens back to me. I also need to try out different zoom, aperture settings and focal distances systematically. I have tried it in different scenarios (close and far objects), but it is difficult to make any accurate conclusions when the exif does not display the AF adjustment data.

I have never experienced problems like that before with my lenses, I was hoping the Star-series had better quality control.
I have never experienced with any Pentax lens that it needed adjustment. From cheap ones to star ones. Guess I am lucky in that. I must admit that I sometimes do not like what I see, but that is very personal. That mostly happens with my three Sigma lenses. But any K,M, A, F or FA lens is never any problem when on any of Pentax camera's and the Samsung GX-10.
But after the quality control by Pentax strange things can happen, someone dropped the box or during transport it was roughly handled. And that may damage a lens and cause malfunctioning....
08-14-2022, 04:30 PM   #14
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QuoteOriginally posted by cport Quote
this is more about the focus plane curvature.
I would love to see a reference for that. It seems like if true the tuning would be possible for the camera to automatically adjust based on a known profile but I donít know of any system that worked that way.
08-15-2022, 03:31 AM   #15
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QuoteOriginally posted by UncleVanya Quote
I would love to see a reference for that. It seems like if true the tuning would be possible for the camera to automatically adjust based on a known profile but I donít know of any system that worked that way.
What reference? This is my personal experience with this lens - two copies, the center AF point very precise, the border points very precise for one copy of this lens, the border AF points not precise for the other copy. But the border AF points required the same correction (which, of course, caused incorrect behavior of the center AF point). Consequently, I am convinced that different copies of this lens might have AF planes with different curvatures. Thus, in-body-correction need not be enough (even the one made for distinct focal lengts).


There might be more problems.

But I love this lens
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