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02-02-2011, 10:43 AM   #1
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Problems with my Tokina SD 70-210mm 1:4-5.6 lens

Hi all.

I've just won this lens on eBay. It's reviewed here: Tokina SD 70-210mm F4.0-5.6 Lens Reviews - Pentax Third-Party Lens Review Database

It arrived to me today. I mounted it on my Asahi Pentax KX, but noticed a problem. When changing to smaller apertures (from f/4 to f/16, say), the lens stops down immediately to the selected aperture. Hence, it's like stop-down metering, and the open-aperture metering of the PK system is gone. This is troubling because when it stops down, the image in the VF gets very dim..even at f/4 it's quite dim. I don't want to use this lens only at wide open aperture.

I then tried it on my ME Super..same problem occurs.

Has anyone had this sort of trouble with this lens?

I think I may have found a cause for it. Refer to the attached picture. Looking at the mount, I can see that the pin is present, but the 'tab' that's supposed to be near the pin is not there. What is the function of the 'tab'? And is it the culprit?

Would appreciate any input. Thanks in advance!


Attached Images
02-03-2011, 02:16 AM   #2
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It is possible that the diaphragm actuator is slightly bent.
This may be due to the 'tab' missing.
Try bending it a bit more to the outside.
It must be reached by the diaphragm release in the body.

See here:

Features and Operation of the Original K-Mount
02-04-2011, 10:36 PM   #3
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Original Poster
blende8: You're right, that's exactly what happened. The pin was bent inwards just a little bit, just enough to make it a problem. What I did was apply some pressure with my fingers to get it straight again & perpendicular to the mount plate. Tested it & now it works fine as it should.

Thanks very much blende8!

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