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02-06-2013, 01:13 AM   #1
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trouble with an AF lens

so, I bought a Sigma 75 200 f3.8 AF lens in K mount. It SHOULD AF on my body, but it doesnt.
Now, I've contacted the seller to hear what might be a problem, but since I've got a new lens I'm very impatient to get it going
what could be the problem? what can I do/try?

02-06-2013, 01:25 AM   #2
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when I manually try to focus it I can feel the engagement of the screw drive (the resistance) opposed to when the lens is not on the camera, but there is no AF
02-06-2013, 02:44 AM   #3
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Since it's a legacy zoom, I'll assume you got it used.

I don't know how Sigma does it with K-mount, but for other brands, they don't actually license the mount technology. So there's a lot of reverse engeneering going on. When the Nikon D7000 was released, sigma repair shops where awash in old lenses that needed new firmware to speak with the new cameras. If you're trying to shoot K5(II(s)), this could be it. Just a thought.
02-06-2013, 03:35 AM   #4
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This is the lens, right? https://www.pentaxforums.com/userreviews/sigma-75-200mm-f3-8-autofocus.html

I had this lens - I believe it was before I had my K-5 (so I used it on my K-x and possibly K200D). I'm pretty sure the AF worked OK, although it may have been slow. I would expect most screw-drive third-party lenses to work as long as the contacts are clean and the lens is well-seated on the camera.

02-06-2013, 03:50 AM   #5
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QuoteOriginally posted by DSims Quote
This is the lens, right? https://www.pentaxforums.com/userreviews/sigma-75-200mm-f3-8-autofocus.html

I had this lens - I believe it was before I had my K-5 (so I used it on my K-x and possibly K200D). I'm pretty sure the AF worked OK, although it may have been slow. I would expect most screw-drive third-party lenses to work as long as the contacts are clean and the lens is well-seated on the camera.
yes, thats the one. I got it for 50 euros, so I dont expect it to have blazing fast AF.
anyone ever tried it with a k5? I'll clean the contacts once i come home and try again
02-06-2013, 04:43 AM   #6
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Try to carefully turn the AF screw with a screwdriver or similar to see if it turns easily. Is the aperture ring set to A or "use aperture ring" set to permitted in camera?
02-06-2013, 04:46 AM   #7
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QuoteOriginally posted by VisualDarkness Quote
Try to carefully turn the AF screw with a screwdriver or similar to see if it turns easily. Is the aperture ring set to A or "use aperture ring" set to permitted in camera?
yes. the ring is set ot A and the use is enabled. When the lens is off camera, when I turn the focus ring, the screw also turns. I'll try the lens on a different body today
02-06-2013, 04:50 AM   #8
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That sounds really weird indeed. And the aperture works flawless? Sound like a contact issue somewhere.

02-06-2013, 05:46 AM   #9
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I have that lens and it works very well on my K5. The AF is adequate. I would also check the contacts.
02-06-2013, 08:21 AM   #10
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QuoteOriginally posted by VisualDarkness Quote
That sounds really weird indeed. And the aperture works flawless? Sound like a contact issue somewhere.
yes, the aperture work flawless. I've set the camera mode to manual an tried controling the aperture with the camera and everything went great. f8 was darker than f4.
I tried cleaning the contacts with a cloth and acetone and it did not help. I was not able to obtain any other camera to try it with. All my other screw driven lenses work fine (DA 40 & 70 )

when I put the lens on the camera I have to input the focal length for the SR system and when I look through the viewfinder it says MF and I cant really see the aperture value in the viewfinder. It always says F-- although it changes the value on the main screen. is that normal?

Last edited by dankoBanana; 02-06-2013 at 08:43 AM.
02-06-2013, 08:51 AM   #11
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the seller just informed me that he used the lens with Pentax SFx and SF7 and it worked fine. hmmmm. I guess theres nothing to do except to go try it with a k20 or a k10 ?
could I have screwed something up in the settings on my camera? I tried reseting all the custom functions in the camera

Last edited by dankoBanana; 02-06-2013 at 08:57 AM.
02-06-2013, 09:44 AM   #12
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With an AF-lens you should not have to put in the focal length so something is wrong indeed. If all other lenses work fine I can't see it's anything with your camera, except maybe some software compatibility with the lens but I haven't heard of such a thing with Pentax. Maybe someone has heard of it?

Does it mount firmly on your camera? I got one lens that sometimes asks for focal length but I just wiggle it and restart the camera ant it's fine. I'm sure there is a subtle variation in the mounts that adds up on my camera and makes them slightly incompatible.
02-06-2013, 09:55 PM   #13
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QuoteOriginally posted by dankoBanana Quote
when I put the lens on the camera I have to input the focal length for the SR system and when I look through the viewfinder it says MF and I cant really see the aperture value in the viewfinder. It always says F-- although it changes the value on the main screen. is that normal?
IIRC when the F-- appears that means you either have to re-seat the lens on the mount or the aperture ring isn't really going all the way to the A setting and locking. And I think a problem with the contacts could effectively do the same thing.

The SFX and SF7 are the first (KAF) AF Pentax cameras - I think I'd feel more comfortable hearing it worked on a PZ-1 (KAF2) or later model, which is the same basic mount as today's DSLRs.

Last edited by DSims; 02-06-2013 at 10:03 PM.
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