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01-07-2014, 08:55 AM   #1
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cant change aperture on "AUTO Chinon f2,8 28mm" mounted to my K-r

Hello fellow Pentax users,
i bought a used lens mentioned in the threads title for about 20 bucks and tested it on my K-r. The good news is, it kinda works, the bad news is I cant change the aperture size by using the aperture ring on the lens.
Every Picture I take Shows the same DOF and same exposure times no matter if i select f11 or f2,8.
Is this the cameras fault, or the lenses faullt, and is there a way to fix this? Does the camera somehow fix the aperture to completely open? If i turn the ring when ist umounted i can see the aperture changing...
I have Firmware 1.14 if that matters...

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01-07-2014, 09:09 AM   #2
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When the lens is off camera, and you change the aperture, does the iris closes/opens or it stays the same!?

If it stays the same (aperture doesn't change), you have sticky aperture blades and they are in need of cleaning.

If they move, but it seems to be a small delay/hesitation, the aperture blades still needs some cleaning - it will get worse in time.
This small hesitation could be just enough for the aperture to stay open all the time when mounted on the camera, while taking the picture.

If aperture does change without any issues but it doesn't change when on the camera, then most probably the small lever is bent and the camera doesn't get in touch with it so your aperture never changes.
If not bent, than something is wrong. Check and see if the lever from the camera actually gets in touch with the one from the lens.

I doubt camera is at fault - especially if other lenses works without any issues.

Last edited by mrNewt; 01-07-2014 at 12:07 PM.
01-07-2014, 09:11 AM   #3
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On my K10, I would use that lens by setting the aperture ring on the lens to the desired stop, setting the camera to "M" manual, focus on the subject, press the green button on the camera. That will set the proper shutter speed and aperture. Then take the shot. Press the green button again to meter for the next shot, and so forth.
01-07-2014, 09:16 AM   #4
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QuoteOriginally posted by Sam Dennis Quote
On my K10, I would use that lens by setting the aperture ring on the lens to the desired stop, setting the camera to "M" manual, focus on the subject, press the green button on the camera. That will set the proper shutter speed and aperture. Then take the shot. Press the green button again to meter for the next shot, and so forth.
Aperture is already selected .

The aperture will close no matter if you press the green button or not.
The only reason you will click the green button is so that the camera can take exposure on the aperture you have selected and to automatically select the right shutter speed for you - because the mount is what we call crippled.

If you know what you are doing and you already have an idea what aperture and shutter speed you need (for that specific ISO), you will never need to click the green button.

01-07-2014, 10:00 AM   #5
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QuoteOriginally posted by mrNewt Quote
Aperture is already selected .

The aperture will close no matter if you press the green button or not.
The only reason you will click the green button is so that the camera can take exposure on the aperture you have selected and to automatically select the right shutter speed for you - because the mount is what we call crippled.

If you know what you are doing and you already have an idea what aperture and shutter speed you need (for that specific ISO), you will never need to click the green button.
I have no clue what I am doing! But I never let that stop me

On my camera and with that lens, the aperture ring on the lens only works in the manual mode. The other way I can use it is the AV mode with the ISO set to Auto. But the lens is always wide open that way, and the camera sets shutter and ISO.
01-07-2014, 11:23 AM   #6
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Is the mount bare metal or anodized black?
01-07-2014, 11:30 AM   #7
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Go into the menus and set "Using Aperture Ring" to "Permitted".
01-07-2014, 12:01 PM   #8
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Can't remember exactly, but as far as I can recall, if you don't set the aperture ring to permitted, you won't be able to actually take any kind of pictures with a manual lens because shutter button won't fire.

01-07-2014, 12:04 PM   #9
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The aperture will never close down unless the camera is in M mode and aperture ring option is set to permitted. BUT, those old Chinons always seem to have sticky blades, so first check it off the camera. It can be cleaned, but very common with those models.
01-07-2014, 03:30 PM   #10
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Thanks for your many replies, i didnt expect hat mich resonanz within such short time :-)
I rly think the Blades are dirty, after taking dozens oft test shots i sometimes could geht the aperture to close. I rly thank you all for your support. I will try to get this lens cleaned asap, since i kinda love the resulsts im getting with it, even if pictures look a little like a painting due to a lack of sharpness with open aperture.
Greetings!
01-07-2014, 03:49 PM   #11
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Ok. Question time.

Can't tell if this is I or M42 mount, can you clarify?

Also, in k mount,-to get the aperture to stop down, you need to be in Manual mode not AV mode. In Av mode the camera fires with wide open aperture.
-Some lenses have black mounts, either painted or anodized aluminum, these are insulating and on some bodies, the camera will not stop down if the aperture pins are not shorted, so sand down the contact area

If M42 you need. To have the pin depressed to activate the apeture
01-07-2014, 04:27 PM   #12
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QuoteOriginally posted by Lowell Goudge Quote
Ok. Question time.

Can't tell if this is I or M42 mount, can you clarify?

Also, in k mount,-to get the aperture to stop down, you need to be in Manual mode not AV mode. In Av mode the camera fires with wide open aperture.
-Some lenses have black mounts, either painted or anodized aluminum, these are insulating and on some bodies, the camera will not stop down if the aperture pins are not shorted, so sand down the contact area

If M42 you need. To have the pin depressed to activate the apeture
As far as I know those are K mount only lenses.
I have a few Chinon Auto, but no 28mm... actually I should get one... hmmm...
01-08-2014, 12:09 AM   #13
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Hi,
its a metal k-mount. I tried it in aperture and manual mode. After a few tries i figured out that it only works sometimes in manual mode... But only sometimes. The funny thing is it got a little bit better after a ton of shots, but its far from working reliable.
01-08-2014, 09:24 AM   #14
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QuoteOriginally posted by luke_mitdermacht Quote
Hi,
its a metal k-mount. I tried it in aperture and manual mode. After a few tries i figured out that it only works sometimes in manual mode... But only sometimes. The funny thing is it got a little bit better after a ton of shots, but its far from working reliable.
Did you ever test the aperture off-camera? If it is sticky, the stickiness should be readily apparent when you flick the actuator lever.


Steve
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