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06-26-2012, 09:47 AM   #1
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Problem: Lens fit, recognition, & focusing

I have a problem with, i think, the contact between the lens and the camera. I hope someone might have a simple solution, rather than a lenghty repair or having to replace my lenses.

I have the problem with both my lenses, which makes me think that this might be something to do with the camera rather than the lenses:
1. The lens appears to be loose on the mount so that the lens is sometimes not recognised (display asks for manual input of focal lenght, or the top display shows "F - - "), with this the autofocus also goes out the window. Pushing the lens into the body, or sometimes twisting it slightly, helps to make the contact and the lens is then recognised by the camera.
Camera: Pentax k-5
Lens: Sigma 28-70mm 1:2.8 EX DG

2. The lens has a similar problem as above, but also has a very soft focus when it works (much like a softfocus filter, or vaseline on the lens)
Camera: Pentax k-5
Lens: Sigma 17-35 1;2.8-4 DG

More info: The problem appeared after a while, so probably not a manufacturing problem. Is intermittent, so it is a slight problem, nothing major (but something I can't have when taking pictures...). The problem of focus occurs in good and bad lighting conditions. And finally, as I have not found a similar problem being described elsewhere I do not think that it is a software problem.

Any advice, or ideas, as to how to fix this would be welcome.

06-26-2012, 10:24 AM   #2
MJL
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The Sigma zooms you have use the "screw" type autofocus system. I suggest to check the contacts & the recessed "screw head" on the lens mounts to make sure they are clean and in working condition. It sounds the camera can control the focus but not accurately, so please also check that small "blade head" like protrusion on the camera mount is not damaged.

You said the 28-70 "appears to be loose on the mount", is the 17-35 doing the same?
06-26-2012, 10:30 AM   #3
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Thanks for your reply.

Yes it is the same for both lenses - when mounted there is no reading for the aperture - on the top screen all it reads is " F -- "

The lenses are not loose, per se, they have a little play (very little) so that when I wriggle them the reading appears, sometime stays, sometimes goes, which suggests to me that the contact is loose.
06-26-2012, 10:30 AM   #4
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when i started reading your link i thought it sounds like my sigma lens...i have the issue with the teleconverter and the 70-200 periodically as well and tweaking the lens usually fix it...i was actually thinking of buying the 28-70 and now wonder if i should get another lens...

06-26-2012, 11:51 AM   #5
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QuoteOriginally posted by pearsaab Quote
when i started reading your link i thought it sounds like my sigma lens...i have the issue with the teleconverter and the 70-200 periodically as well and tweaking the lens usually fix it...i was actually thinking of buying the 28-70 and now wonder if i should get another lens...
From what Pearsaab describe, I think it is an electronic (information transfer) or mechanical (autofocus drive) contact alignment issue between these Sigma zooms & K5. I suggest to mount these lenses onto another AF Pentax camera (even the AF film SLR will do) to see whether they behave the same.
06-26-2012, 01:10 PM   #6
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MJL: I did not have this issue with my ist*DL, so you might be right in that it is a contact issue - as I have suspected as well - is there some sort of solution to this problem that you might be able to suggest? greasing the contacts, or using an alcohol solution, or sand-papering them a bit? They look clean to me and I rather have someone suggest something before I spray WD40 into my camera... (which I would apply with a cotton swap rather than spraying it, of course...)

peersap: if the contact issue is one that is persistent and ubiquitous with this combination then I would have thought that this problem would have popped up, and been discussed, in various other fora. Since it has not been mentioned anywhere (at least to my knowledge) I would recommend the 28-70 2.8 - it is an excellent, and versatile lens - it beats the 18-250 hands down...
06-26-2012, 10:33 PM   #7
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Hi Ilchkai,

Did you have a chance to look at the small C-shape retention springs just below the lens mount on the camera? There are 3 of them and separated about 120 degree from each other. I notice if I mount a lens to an older camera body with flatten (old) C springs, there will be a small play like what you describe. That I think may created a loose contact or mis-alignment between the lens & camera. The C-springs on my K5 are not in exactly same shape but all extend fully, so there is no play.

Since both of your zooms behave the same on the same camera, plus the "small play" I experimented above. That lead me to believe that the problems has a mechanical origin on your K5, mostly likely with the retention/locking mechanism below the bayonet mount.

Is your camera still under Warranty? I would certainly not recommand WD40 or sandpaper if that is the case. You can clean the lens mount and contact points with small amount of lens cleaner fluid or alcohol, that did the trick for me nicely. Good luck.
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