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11-14-2011, 05:49 PM   #1
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Having an issue with Vivitar 28mm f2.8 lens

I can't seem to figure out how to get my Vivitar 28mm f2.8 lens (the K21 in the bestiary, Great Vivitar 28mm Bestiary: Details) to work properly on my K-r. Namely, pressing the green button doesn't seem to make it stop down, so it will only meter properly wide open. If I stop it down, when I take the picture, the aperture is clearly working right, because, using the green button exposure settings, it's appropriately underexposed (ie, it's metering for f2.8 but I've actually got the lens aperture set to f8, so it's dark). I've got a Pentax-M 50mm that works just fine with the green button, and the only setting I change when swapping the lenses is the focal length. Do I have a bum lens or a setting not right? Or does this lens just not work with the green button and I have to do the mental math to expose it properly at anything except wide open? Thanks.

EDIT

I narrowed the problem down to the data pins not being shorted (using a piece of aluminum foil to short the pins, and the green button functions regularly). Now, does anybody know of a better way of shorting those pins (just for this lens)?


Last edited by grsing; 11-15-2011 at 04:59 AM. Reason: Identified problem
11-14-2011, 06:13 PM   #2
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Check the aperture lever on the back of the lens- does it move freely?

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11-14-2011, 06:27 PM   #3
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Yeah, it moves crisply, and the more the aperture ring is set to a smaller aperture, the less it moves, just like the 50mm (moving the lever is closing down on the aperture, like it should).
11-14-2011, 06:53 PM   #4
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It needs to be in manual mode

Also is the base of the lens black or silver?

11-14-2011, 07:08 PM   #5
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It's in manual. The back of the lens is black plastic (the 50mm that works fine is grey metal, if that makes a difference)
11-14-2011, 09:55 PM   #6
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I've not had this problem, as I don't have a lens with a plastic mount lthat doesn't have all the contacts, but it sounds like it might be an issue with the plastic not shorting the data pin. The only lens I have that doesn't short the pins, is my Helios 44m-2 on M42-PK adapter that doesn't even touch the the pins, but because it's M42, it doesn't have the aperture lever like K mounts.

"experts" and more experienced, what ye say? Is this a pin short problem, or something maybe with the lens itself?


----EDIT----

Is the lens in the OP the actual lens, or for point of reference to the exact type of lens? If it's the exact lens, looks like there are drill holes on the front ring - maybe some "repairs" were done that are affecting metering (though who knows what those'd be...??)

Last edited by pezmaker; 11-14-2011 at 10:10 PM. Reason: point of clarity
11-15-2011, 05:00 AM   #7
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The lens in the sample photo appears to be a non conducting mount, I can't tell if it is plastic or painted but it needs to short pin 7 the data pin to the lens mount to make the camera think a lens is attached
11-20-2011, 11:09 AM   #8
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Hello grsing

One way to do it is to scrap the black ink out of the mount in the region that contacts with the data pins when the lens is completely inserted on the camera - that’s what I did to my k22 model, and it works perfectly.

Best regards,

11-20-2011, 03:20 PM   #9
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QuoteOriginally posted by ddharriman Quote
One way to do it is to scrap the black ink out of the mount in the region that contacts with the data pins when the lens is completely inserted on the camera - that’s what I did to my k22 model, and it works perfectly.
The K22 is plastic mount, not painted metal. The trick with this is to get inexpensive shiny metal duct-sealing tape - NOT common grey (or colored) plasticized fabric duck-tape / duct-tape. I use a bit of this tape on the bases of many lenses, especially M42's. As long as the lens base will cover the contact pins, such tape works fine.

Where NOT to use such tape: Don't put any on PK macro tubes, mount-reverse adapters, wide-flange M42-PK or M39-PK adapters, T-mount or T2 adapters -- not on anything BUT lenses themselves. Most of these adapters fit tightly to the camera mount. The thickness of the metal tape can cause them to jam onto the mounts. For these kinds of adapters, just scrape off the paint -- I use the file tool on my Leatherman.
11-20-2011, 04:31 PM   #10
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That mettalic - aluminium ( correct spelling ) tape is generally used by heating engineers, if you know one I'm sure you could scrounge a bit. I use it on some of my lenses and lasts a long time.
11-23-2011, 08:12 PM   #11
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I'll have to see if I can scrounge any of that tape up, thanks for the suggestion!
11-26-2011, 02:48 PM   #12
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«The K22 is plastic mount, not painted metal…”.

Sorry, did not knew that, and of curse being the base plastic, ignore my advice.

Best regards,
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