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03-21-2013, 04:48 PM   #1
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Aperture Problem w/ K10D

I recently got a telephoto lens (Cosina 100-300mm AF) dirt cheap, but just today noticed that the aperture doesn't close when I mount this lens on the K10D. I mounted this on my ZX-7 and everything works as it should. I took my DA 16-45 and made sure it worked on the K10D and it works perfectly.

So what am I missing that allows the Cosina lens to work properly on one camera, but not the other? Any ideas?

03-21-2013, 05:53 PM   #2
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Is the mount of the lens chrome (bare metal) or black (anodized)?

If it's black, the problem and solution may be the same as in this thread.
03-21-2013, 06:17 PM   #3
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If the lens has an aperture ring but without the 'A' setting you must set the custom function "Using aperture ring" to "Permitted". You can leave the setting at that also when you use your other lenses.

If the lens does have the 'A' setting make sure to leave it in 'A' at all times.
03-22-2013, 02:18 PM   #4
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I have used FA lenses on this body before. A Pentax 28-80 and a Tamron 28-200 to be exact. Both of these work great with the film bodies and fine on the K10D. Aperture ring and all which, unless I'm shooting with the ZX-5n, always stays on A.

This lens has the A setting on the aperture ring. Works great on the ZX & MZ bodies. I have aperture ring enabled on the K10D and have discovered today that if I shoot the lens as though it were an older M, K, or A lens (meaning shooting in Manual, green button to stop-down meeter, fire) it works. But should I shoot any other mode or put the aperture to A, the lens will not stop down. Not when doing a DOF preview or when releasing the shutter.

As for the mount, it is chrome. Looks just like any Kaf mount on any of my other lenses. I even took the time to clean the contacts on both the lens and the body to see if that had any affect. The camera knows what the available aperture is on the lens as it changes appropriately as I zoom, so I know it's communicating. I just don't understand why this is the only lens I'm having to treat this way in order to use. And it is only with the K10D and not with any of the two other AF film bodies I have. It just seems so strange.

03-22-2013, 02:22 PM   #5
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Well you've already done all the simple straight forward things that spring to mind immediately, that I would have suggested for these sorts of issues.

We'll just have to wait for some really clever person to come along the the right solution for you.
03-22-2013, 02:38 PM   #6
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Can you post a photo of the lens mount? I don't know what I'm looking for. But the photo may trigger something.

A photo of the camera's lens mount may help too.
03-23-2013, 11:37 AM   #7
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In case it sheds any light on the issue, here are the lens specs.

Cosina 100-300mm f/5.6-6.3 MC Macro

Here is a photo of the lens mount.
Attached Images
 
03-23-2013, 01:15 PM   #8
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OK, I don't see anything unusual about the lens.

How about the camera's lens mount? This is my K10D with the aperture actuator in "normal" position (green arrow). In normal position, the lens is at full aperture (wide open).

Without a lens attached, push the shutter release of the camera and notice the aperture actuator. It should go up to the red arrow position, closing the lens's aperture, and then go down to normal position. Please test your K10D and post back.

Note: K-7, K-5 (and probably K-r, K-01, and K-30) have different behavior: without a lens attached, the aperture actuator doesn't move.

Attached Images
View Picture EXIF
PENTAX K-7  Photo 

Last edited by SOldBear; 03-23-2013 at 01:22 PM.
03-23-2013, 01:37 PM   #9
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QuoteOriginally posted by SOldBear Quote
OK, I don't see anything unusual about the lens.

How about the camera's lens mount? This is my K10D with the aperture actuator in "normal" position (green arrow). In normal position, the lens is at full aperture (wide open).

Without a lens attached, push the shutter release of the camera and notice the aperture actuator. It should go up to the red arrow position, closing the lens's aperture, and then go down to normal position. Please test your K10D and post back.

Note: K-7, K-5 (and probably K-r, K-01, and K-30) have different behavior: without a lens attached, the aperture actuator doesn't move.
That part works fine on the K10D. I've observed it as you describe. It moves as it should and the aperture on every other FA & DA lens I have works works as it is supposed to.
03-23-2013, 03:19 PM   #10
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I gave up.

If the camera's aperture actuator works fine (confirmed with "no lens" test), and the lens's aperture lever works fine (manual mode works). What makes them not working together?
03-23-2013, 09:05 PM   #11
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Thanks for all of the help.

It is puzzling why this one lens behaves this way. Funny thing is that when I put it on my ZX-7 it works great. I can not understand why this is the only lens that doesn't function as it's supposed to on the K10D. Has anyone else had a problem with Cosina or non-Pentax brand lenses exhibiting strange behaviors on a digital body?
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