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07-10-2012, 03:27 AM   #1
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My first PKA lens a flop? Please help.

Hi everyone!

Although this is my first post here, i'm not a complete Pentax novice, as i've been using a nice Spotmatic F for quite some time now. However, i 've always considered it more of a "M42" rather than a "Pentax" camera (looks like it's the mount that defines a camera, isn't it?).

Recently, to get advantage of the small size and the nice lenses i got myself a nice ME Super and ordered a Pentax-M 1.7/50 and a Sigma mini-wide 2.8/28 to go along with it. (with a Pentax DSLR down the road maybe?) The Sigma arrived yesterday in mint condition, complete with hood, caps and case.

However there seems to be a problem from the beginning, as after fitting the lens onto the camera, the aperture ring refused to go wider than 4.0, even though off-camera the aperture ring turned all the way from 22 to 2.8. Removing and re-fitting the lens corrected that (sigh of relief).

The problems remained however, as there seems to be a breakdown of communications between the lens and the camera. More specifically, the camera seems to constantly underexpose (2.8 straight at the sun, ASA 400, the speed is 1/250 and 2s indoors) and the shutter speeds do not change despite changing the aperture.

I am not familiar with the Pentax bayonet, but it seems to me the small lever in the groove (green arrow) should be the one telling the camera what the aperture is, and extent of its movement should be according to the aperture when the other lever (magenta) is moved as the shutter fires. With the tall (magenta) lever held down, changing aperture should cause the small lever in the groove to move to an extent dictated by the chosen f value. Problem is the small lever just moves one click (from 2.8 to 4.0?) and then stops, despite continuing to turn the aperture ring. When the tall lever is to its resting position, using a toothpick i can move the small lever freely along its groove without any changes to the aperture or any resistance. If i abruptly tap the large lever, the small lever travels a little further along its groove, but for distances that are not always constant, aperture value being the same. Is any of this normal? I'm pretty sure it's a lens problem and i'll probably have to send it back. If you recognize the problem, it would be great if someone could explain it to me so that i can claim a refund for the lens.

07-10-2012, 03:45 AM   #2
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There should be a picture of the lens mount there. Also i must add that the lens is the initial mini - wide, not the II version.

07-10-2012, 05:00 AM   #3
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When a K-mount lens is unmounted turning the aperture ring should change the aperture. You should also see the small lever turn as you turn the aperture ring. There is something wrong with your lens.
07-10-2012, 10:46 AM   #4
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Thanks for the reply. I understand this lever is called aperture coupling lever yes? It is faulty indeed as it should normally move as the aperture ring turns. However, what is funny is the fact that the situation i described above occurs when the lens is mounted wide open (ie coupling lever all the way down). If the coupling lever is somewhere in the middle (ie f8) when i mount the lens to the camera, the shutter speeds respond to the changing apertures, only at excessively fast speeds, eg 1/1000 when my digicam for the same aperture and ISO will choose 1/125. Luckily, i am negotiating either a refund or an exchange for a mini wide II PKA version.


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