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01-29-2010, 07:48 PM   #1
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K-7 & Metering A Cosina 50mm Manual Lens...

Sorry if this is a repeat question..I did do a search but did not find the specific answer I might need to know!

I have a Pentax K-7 and just mounted a fully manual Cosina 50mm f2.0 on it. I have never used this lens before on the K-7 and I can't seem to get accurate and reliable metering when using this lens.

(This lens has absolutely no contacts on it!)

I am using the camera in manual mode, and set the metering to evaluative, and usually (on my K200D) I could press the green button, and the K200D would get a pretty accurate meter reading and adjust the aperture and shutter accordingly.

Here's what I am finding on the K-7:

No matter what aperture I set the lens at, the camera seems to think the lens is wide open and selects very fast shutter speeds. If I press the green button, I do see some shutter value changes, but they are very fast...suggesting it's reading the lens as wide open. There seems to be no effort from the camera to select an aperture.

At ISO 100..the camera seems to think I need a shutter of 1/3000 or more.

I have tried playing with EV and that really doesn't make to much difference in my opinion.

Am I doing something wrong here?

Thanks for any tips or help you can provide.

Richard

01-29-2010, 11:35 PM   #2
Igilligan
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Is it a K mount or M42?

some of the M42 lenses have a pin on the back that closes the aperture. If that pin is not depressed... the lens is always wide open on the camera, no matter what ap you set it at.


If it is a regular K mount M lens, you should see the aperture closing as you turn the ring. And the camera should meter to the closed ap.
01-30-2010, 12:09 AM   #3
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Oily aperture blades maybe? If it's K mount, press the blade on the mount side and see if the iris blades are responsive. The blades should close fast for the lens to be usable stopped down. If they don't, then you need to take the lens for a cleaning.
01-30-2010, 05:44 AM   #4
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QuoteOriginally posted by Igilligan Quote
some of the M42 lenses have a pin on the back that closes the aperture. If that pin is not depressed... the lens is always wide open on the camera, no matter what ap you set it at.


If it is a regular K mount M lens, you should see the aperture closing as you turn the ring. And the camera should meter to the closed ap.
Thanks for the help..I should have mentioned it was a K-Mount Lens. I agree with what you say, but the camera is not responding to any aperture changes I make.

QuoteOriginally posted by Laurentiu Cristofor Quote
Oily aperture blades maybe? If it's K mount, press the blade on the mount side and see if the iris blades are responsive. The blades should close fast for the lens to be usable stopped down. If they don't, then you need to take the lens for a cleaning.
I wish that were the case (well not really..lol), then I would understand what might be wrong.

When the lens is off the camera the blades are perfect and move freely as I select different apertures and press the blade on the mount side. When on the camera...nothing happens??? This has got me stumped!!

Thanks for the help anyway ;-)

01-30-2010, 07:16 AM   #5
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if you are in AV mode the pentax cameras (All of them) shoot wide open only

In manual mode they willl stop down to the set aperture of the lens.

You can check this witht he DOF preview (on the on/off switch) or with the green button..
01-30-2010, 11:28 AM   #6
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QuoteOriginally posted by Lowell Goudge Quote
if you are in AV mode the Pentax cameras (All of them) shoot wide open only

In manual mode they will stop down to the set aperture of the lens.

You can check this with he DOF preview (on the on/off switch) or with the green button..
Thanks for the info Lowell. I had the same understanding as you have described here, but this is the problem I'm having...the camera will not stop down regardless of what aperture I select and pressing the green button seems to do nothing.

On my K200D when I pushed the green button, there was a mechanical action involved with getting a meter reading and the camera selecting the program line..on the K-7...no mechanical action.
01-30-2010, 12:25 PM   #7
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have you enabled the aperture ring setting on the camera body?
01-30-2010, 12:27 PM   #8
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Custom setting?

I am not sure about K-7 but many of the other models require a custom setting to enable use of manual lenses.... I think the name of the setting is different on different models.

The K100D has something like "enable use of aperture".

Sorry I cant check right now as my camera is in the shop

01-30-2010, 12:41 PM   #9
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QuoteOriginally posted by PentaxFan Quote
On my K200D when I pushed the green button, there was a mechanical action involved with getting a meter reading and the camera selecting the program line..on the K-7...no mechanical action.
And you're definitely in M mode? If so, something is indeed wrong. Can you test the lens on the K200D or another camera?
01-30-2010, 02:20 PM   #10
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QuoteOriginally posted by gabriel_bc Quote
have you enabled the aperture ring setting on the camera body?
Yes I have! Thanks for the suggestion ;-)

QuoteOriginally posted by kmccanta Quote
I am not sure about K-7 but many of the other models require a custom setting to enable use of manual lenses.... I think the name of the setting is different on different models.

The K100D has something like "enable use of aperture".

Sorry I cant check right now as my camera is in the shop
Yes...I have set all the settings that I can find...I have done this before on my *istDS2 & my K200D! Thanks for the help ;-)

QuoteOriginally posted by Marc Sabatella Quote
And you're definitely in M mode? If so, something is indeed wrong. Can you test the lens on the K200D or another camera?
Marc...Oh yes...I'm very sure I am in M mode. (It's the only mode...LOL) And yes...on all my other bodies...I can get it to work the way it should. This is why I posed the question and am confused that it won't work on the K-7...LOL
01-30-2010, 10:15 PM   #11
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It should work on the K-7. If the lens works fine on other cameras, maybe your K-7 has a problem.
01-31-2010, 07:00 AM   #12
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I have encountered this problem before on my cosina 50/1.4. The lens worked fine on my K100D, but I ran into the exact same issue you have when used on the K7. It seems that the aperture lever on the lens does not match well with the aperture actuator of the K7. Once you fit on the lens, its pushed to wide open and when the camera tries to activate the lever upon 'green button' or shutter release, it fails to move the lever.

I have many other manual lenses and this has been the only case. Sadly, I did not find a solution to this and subsequently sold the lens to another pentaxian who did not mind as he had a K20D and also shot film cameras.
I did like the Cosina 50/1.4 alot.
01-31-2010, 12:43 PM   #13
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Interesting theory on the aperture lever not being a good match for the K-7. I have no idea about that, not knowing this lens or camera. That aside, if the lens works on other bodies, then I guess the next test is to see if other manual K-mount lenses fail on the K-7. If so, then I guess you can safely assume it's a camera problem - although not knowing your camera, I still wouldn't completely rule out the problem being a camera setting that I don't know about, or something as simple as contacts that need cleaning.

Last edited by Marc Sabatella; 01-31-2010 at 12:50 PM.
01-31-2010, 05:09 PM   #14
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QuoteOriginally posted by Marc Sabatella Quote
Interesting theory on the aperture lever not being a good match for the K-7. I have no idea about that, not knowing this lens or camera. That aside, if the lens works on other bodies, then I guess the next test is to see if other manual K-mount lenses fail on the K-7. If so, then I guess you can safely assume it's a camera problem - although not knowing your camera, I still wouldn't completely rule out the problem being a camera setting that I don't know about, or something as simple as contacts that need cleaning.
Certainly not a contact problem. Mine did not have any contacts. Neither did it occur on any other lens. But i did notice that the Cosina lever was thinner than that of my other lenses. Perhaps if TS can swap out this lever with that from some other lens. Oddly it is also a Cosina.
However, I do have a Cosina 24/2.8 that works fine, but it is a PK-R lens.
01-31-2010, 07:23 PM   #15
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QuoteOriginally posted by pinholecam Quote
I have encountered this problem before on my cosina 50/1.4. The lens worked fine on my K100D, but I ran into the exact same issue you have when used on the K7. It seems that the aperture lever on the lens does not match well with the aperture actuator of the K7. Once you fit on the lens, its pushed to wide open and when the camera tries to activate the lever upon 'green button' or shutter release, it fails to move the lever.

I have many other manual lenses and this has been the only case. Sadly, I did not find a solution to this and subsequently sold the lens to another pentaxian who did not mind as he had a K20D and also shot film cameras.
I did like the Cosina 50/1.4 alot.
I'm so glad you chimed in and thanks....I think you just might be correct here! My other lenses work fine when I try them in manual on the K-7! Thanks for the tip ;-)

QuoteOriginally posted by Marc Sabatella Quote
Interesting theory on the aperture lever not being a good match for the K-7. I have no idea about that, not knowing this lens or camera. That aside, if the lens works on other bodies, then I guess the next test is to see if other manual K-mount lenses fail on the K-7. If so, then I guess you can safely assume it's a camera problem - although not knowing your camera, I still wouldn't completely rule out the problem being a camera setting that I don't know about, or something as simple as contacts that need cleaning.
Thanks for your input and food for thought ;-) As mentioned above...other lens work in Manual Mode with a press of the green button!

QuoteOriginally posted by pinholecam Quote
Certainly not a contact problem. Mine did not have any contacts. Neither did it occur on any other lens. But i did notice that the Cosina lever was thinner than that of my other lenses. Perhaps if TS can swap out this lever with that from some other lens. Oddly it is also a Cosina.
However, I do have a Cosina 24/2.8 that works fine, but it is a PK-R lens.
Thanks Again...I think you have provided a sound reason for this problem ;-)
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