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06-17-2014, 02:38 PM   #1
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Cosina 70-210 wont work properly

Hi all

I just bought this lens in a beautiful shape, everything working alright:

COSINA 70-210mm f/4.5-5.6 PK Mount Camera Lens - RB M29 | eBay

The problem is I can't make is work with my K5. Although I rotate the aperture ring, measuring the light with the green button doesn't stop down the lens. Nothing happens and the lens is always full open.

- I have other manual lenses an they all work properly with the K5 (Pentax M 50mm, Tokina 300mm 5.6, Vivitar 75-260mm just to name a few)

- The Cosina works great with my film cameras (P30, K1000)

Anyone have any ideas?

Thanks, Sev.

06-17-2014, 02:44 PM   #2
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It looks like the outer rim of the mount is painted black. You may have to scrape/sand to bare metal so that it shorts out the electrical contacts on the body. Otherwise, the camera will not know that a lens is mounted.
06-17-2014, 02:51 PM   #3
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Is this your first manual focus lens?

Is the "Use aperture ring" menu option set on? Is the "Optical preview" option set on?

Adam wrote an article on how to use MF lenses.
https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html
06-17-2014, 03:02 PM   #4
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@ lmd91343 - I have other manual lenses (I've listed some of them in the original post) and they all work correctly. And I have read that excellent post from Adam more then once Everything is well configured in the camera!

@ OregonJim - Don't tell me that I have to scrape this beautiful lens to make it work? If that is the case, and since I have other lenses in the same region, I think I will let it pass and use it on film

06-17-2014, 03:16 PM   #5
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Sorry, that's all I've got. Sounds like you've covered the basic troubleshooting.
06-17-2014, 03:17 PM   #6
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You shouldn't need to scrape it, the K-5 doesn't care about that I don't think. (Some later models do apparently.) You do have to put the camera in M mode, have the green button set-up properly, etc, but it sounds like you know that already.

So does the aperture and lever work on the lens when it is not mounted? If you push the lever all the way back (so it opens the aperture) and put a little extra pressure on it and then release, does it release or does it get stuck? (Not uncommon.) Is the lever slightly bent outward? (Sometimes this gets it stuck once mounted.)

Last edited by vonBaloney; 06-17-2014 at 03:23 PM.
06-17-2014, 03:37 PM   #7
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Thank you all for your answers so far!

@ vonBaloney - The lever works fine at all apertures, and doesn't get stuck in any way. And it is not bended also, it is just like the others from other lenses.
06-17-2014, 03:43 PM   #8
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QuoteOriginally posted by Sevandija Quote
Thank you all for your answers so far!

@ vonBaloney - The lever works fine at all apertures, and doesn't get stuck in any way. And it is not bended also, it is just like the others from other lenses.
Optical preview work to stop it down? It is possible that it does need conductive contacts although the green button should work fine to set the shutter speed. But possibly not actuate the lever -- it is a weird combo (K-mount with black metal). Test it with a little bit of foil tape on the mount and see if it wakes up -- if it does then you will either have to scrape the paint off (or use the foil tape all the time, but that makes it hard to mount) or remove (or chop off) the aperture lever so that it works like an m42 lens (will stop down as you turn the ring)...

06-17-2014, 04:46 PM   #9
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QuoteOriginally posted by vonBaloney Quote
You shouldn't need to scrape it, the K-5 doesn't care about that I don't think.
I'm pretty sure it's necessary for all Pentax dSLRs.

Not usually needed for K-mount lenses, as the mount is usuallly bare metal - but this one is not.
06-17-2014, 04:51 PM   #10
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QuoteOriginally posted by OregonJim Quote
I'm pretty sure it's necessary for all Pentax dSLRs.

Not usually needed for K-mount lenses, as the mount is usuallly bare metal - but this one is not.
Well, it is not necessary on the K-5 for non-K-mount lenses -- m42s, t-mounts, whatever. The green button works fine even with no lens at all. The aperture lever however may be another story as it is fairly unusual to have a non-conductive K-mount with aperture lever. (I know my old K10D would try to actuate the lever even with no lens.) Of course I could test my K-5 with no lens right now, but I'm just too lazy to get up...but you're probably right. So it is either scrape it or lose the lever...
06-17-2014, 09:05 PM   #11
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QuoteOriginally posted by vonBaloney Quote
(I know my old K10D would try to actuate the lever even with no lens.
Yep. The K10D doesn't care.


Steve
06-17-2014, 09:50 PM   #12
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There was a change in the software , I can't say exactly what model of camera, where the camera requires the pins to be shorted to the lens mount for the aperture mechanism to function. The *istD and K10D can work without this, but the K7D and later cameras cannot. This was first addressed with extension tubes and teleconverters, but clearly it also applies to lenses.

I don't know why it was done, but it seems to be here to stay

Some people put thin aluminum tape on the base of the lens inthe correct location. But I don't agree with this approach because it then allows contamination of the pins on the lens mount dune to adhesive from the tape. Since the value of the lens is largely based upon working with pentax DSLRs, it does not really devalue the lens to sand the paint off the mount in the appropriate area
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