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04-20-2021, 06:54 AM   #1
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Ever had a lens/body combination which just won't work?

I have a DA18-250 which just won't AF on my K-7. It works fine on my ancient *istD and my K-1 II but just racks along the full focus travel before giving up and stopping out of focus on the K-7. All my other DA lenses work fine on the K-7 as do other slow tele zooms like the F100-300. So it seems there is something about this combination that fails. Both body and lens are well out of warranty of course and I won't waste any money trying to get them to play nice.

Any body else have combo's which are incompatible for no obvious reason?

04-20-2021, 07:09 AM   #2
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I never had an issue like that, but I owned 2 copies of the Meyer-Optik Görlitz 135mm f2.8 lenses, 1 wouldn't reach infinity focus while the other went beyond infinity with my camera. Luckily the M42 mounts where interchangeable so both worked fine with my K-3 afterwards
04-20-2021, 07:10 AM   #3
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QuoteOriginally posted by steephill Quote
Any body else have combo's which are incompatible for no obvious reason?
The only time I experienced a mismatch was with my DA* 50-135 and K-5 (or K-5 II, don't recall exactly). The lens would not autofocus reliably at the longer focal lengths from about 120 to 135mm. I suspect the issue might have been caused by the lens's failing focus motor (i.e., SDM). It worked properly after the lens was repaired, and when subsequently converted to screwdrive.

Could the problem be caused by a serious front- or back-focus issue? Have you calibrated the lens via the AF Fine Adjustment setting?

- Craig
04-20-2021, 07:23 AM - 2 Likes   #4
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Does it work in liveview? If it does have you tried to clean the autofocus sensor in the k-7?

Context:
Dirty autofocus sensor - PentaxForums.com

In theory I’d expect the other slow long zoom to struggle also but as they are not identical lenses perhaps one is more negatively impacted than the other.

04-20-2021, 07:24 AM - 3 Likes   #5
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The problem might be as simple as some dust or a hair in front of the PDAF lenses on the floor of the K-7's mirror box. "Slow" lenses like the DA18-250 project a fairly narrow beam of light into the camera's AF system so they are more susceptible to this.

To fix it, set your camera to "sensor cleaning" mode and use a blower to remove any dust around or in the depressions on the floor of the mirror box. (You might as well blow off the sensor, too, while you're at it.

Hope that helps!

P.S. See @UncleVanya's post!
04-20-2021, 07:33 AM   #6
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my *istD and tamron 28-75/2.8 on my K10 it focused fine, but on the *istD it would focus perfect until the last adjustment which put it a little off
04-20-2021, 08:34 AM   #7
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I have the exact same issue with the 18-250 and the K-7. The lens works perfectly on K-3, K-10 and *istDS. Other lenses work fine on the K-7. In addition to poor autofocus generally, the lens will rarely reach infinity focus even with maximum AF lens correction. Comforting to hear that another forum member has this issue. I am personally baffled so just avoid this lens/body combination
04-20-2021, 10:21 AM   #8
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Interesting. I have never had any problem with my Tamron 18-250 on K-7 (the lens Pentax DA 18-250 is based on).

04-20-2021, 11:22 AM   #9
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I have Sigma fisheye 2,8/10, which is a very nice lens for its purpose. However, K-5 does not recognise it correctly. It registers the lens in the EXIF data as Sigma 70-200 mm (!) and the shake reduction SR acts horribly wrong. Without SR the lens is operable, but the EXIF data still wrong.

Even worse with K-1: the camera locks up (freezes) when I try to switch it on with this Sigma 2,8/10. No matter if the body is set to FF or crop mode.

Is there an obvious reason for this? Maybe in case of K-5, that the camera firmware is too old to recognise the lens - or that the lens firmware is buggy. For K-1 - I've no idea.

---------- Post added 04-20-21 at 09:28 PM ----------

QuoteOriginally posted by c.a.m Quote
The only time I experienced a mismatch was with my DA* 50-135 and K-5 (or K-5 II, don't recall exactly). The lens would not autofocus reliably at the longer focal lengths from about 120 to 135mm. I suspect the issue might have been caused by the lens's failing focus motor (i.e., SDM). It worked properly after the lens was repaired, and when subsequently converted to screwdrive.

Could the problem be caused by a serious front- or back-focus issue? Have you calibrated the lens via the AF Fine Adjustment setting?

- Craig
I have needed to fine tune the AF via camera menu a couple of times. E.g. SMC-F 2,8/135 when used with K-3 - a clear case of front focusing, and I missed a few otherwise very nice shots because of that, before I learned to fix it. But as long as it's fixable, I wouldn't say it won't work.

In addition, I used to have occasional focusing problems with DA 17-70 and K-5, but it must have been the SDM defect with the lens irrelevant to the body.
04-20-2021, 11:45 AM   #10
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My K-5 with the FA 35mm/2, somehow it would never achieve perfect focus. It made me scratch my head about the FA 35, which has quite a good reputation between pentaxians. Once I got the K-1 it really did shine, and I realized the problem was with the K-5
04-20-2021, 12:20 PM   #11
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Useful to hear I am not the only one having trouble with this combo. I have cleaned the focus sensor a few times over the years but it doesn't make much difference. The lens might behave for a shot or two but it reverts back to non-performance quickly. I just find it odd that no other lens behaves like this on the K-7 and the lens works fine on other bodies, one much older and one much newer.
04-20-2021, 12:20 PM   #12
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QuoteOriginally posted by steephill Quote

Any body else have combo's which are incompatible for no obvious reason?
Pentax K5 body and any AF lens I put on it in any light other than broad daylight.
04-20-2021, 12:57 PM - 1 Like   #13
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QuoteOriginally posted by UncleVanya Quote
Does it work in liveview? If it does have you tried to clean the autofocus sensor in the k-7?

Context:
Dirty autofocus sensor - PentaxForums.com

In theory I’d expect the other slow long zoom to struggle also but as they are not identical lenses perhaps one is more negatively impacted than the other.
QuoteOriginally posted by photoptimist Quote
The problem might be as simple as some dust or a hair in front of the PDAF lenses on the floor of the K-7's mirror box. "Slow" lenses like the DA18-250 project a fairly narrow beam of light into the camera's AF system so they are more susceptible to this.

To fix it, set your camera to "sensor cleaning" mode and use a blower to remove any dust around or in the depressions on the floor of the mirror box. (You might as well blow off the sensor, too, while you're at it.

Hope that helps!

P.S. See @UncleVanya's post!
Thanks gents!
04-20-2021, 02:05 PM   #14
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QuoteOriginally posted by UncleVanya Quote
have you tried to clean the autofocus sensor
OK, I feel dumb. Where would I find the autofocus sensor on a K-5IIs and a KP?
04-20-2021, 02:12 PM - 1 Like   #15
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QuoteOriginally posted by steephill Quote
Ever had a lens/body combination which just won't work?
Aye most of my harem, when my body has had too many drams...

Last edited by Kerrowdown; 04-20-2021 at 02:59 PM.
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