SMC-A 50mm f1.7 - a 'problem' and a question.

The problem is easily solved - I can focus on the K10D screen easily (I started out with a Zenit 3m - plain screens don't scare me :wink. Unfortunately, depending on whether I am wearing my glasses, which pair (reading or distance) and how the correction dioptre thingy is set, what I see as in focus and what the sensor sees as such may not be the same thing. Anyway, an hour or so with a fixed target, a tripod and careful notes about what was used should give me the answer to that.

The question may be more important. The lens seems to work fine in Av mode - slightly underexposed, but otherwise OK. However, the aperture ring will only turn from 1.7 to somewhere between 8 and 11. Won't go as far as 16, 22 or A.

Is this normal, or do I have a real problem?

ETA: Solved. The lens has a problem. I took it of the camera and the ring won't turn past 8/11. Oh well, it seems to work OK otherwise.

Great lens. Very underrated. Must be something wrong/bent inside. Hardly worth repairing when you can pick up a mint one for about £40. Well worth buying another.

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I probably won't bother. It works after a fashion and I only thought I'd give it a try because I've just bought a couple of cheap lenses for a couple of my other 10MP cameras and didn't want the K10D to feel left out.

Puzzled! How can you use it in Av mode if you can't set the lens to A, well at anything other than full aperture?

Having re-read the relevant (though slightly confusing) pages in the manual, yeah, you are right.

Though why, to use Aperture priority you should need to set the lens to A, normally used for Shutter priority, is beyond me. I get the impression Pentax made a mess of their legacy lens provision development.

Oh well, I'll just bin the lens and when the K10D gets used it will be with the kit lens only.

Modern lenses tend not to have aperture rings and aperture is controlled by the camera body instead. For an older lens to be used in this way it needs an A on the aperture ring to enable it. That's why even for Av the A setting should be used.

If you really want to use the aperture ring instead, you can do using manual settings.

If the lens in question won't move to some apertures then the ring is faulty. I think some early SMC Pentax-A 50mm f/1.7 lenses were susceptible to aperture ring faults.

Thanks for the info John, but it doesn't change my opinion on Pentax's development team.

Pentax lenses even the A series were quite well made and can be taken apart unlike similar lenses from other makers that were glued together.

I remember now the aperture ring problem is due to a plastic rivet snapping. It can be replaced with a small screw or (fingers crossed) a bit of epoxy glue. I'm quite sure the f/1.4 has a screw + possibly the last f/1.7's

Details here ..... There's PDF and a Youtube video in that thread.

https://www.pentaxforums.com/forums/114-maintenance-repair-articles/88051-pentax...


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The A 50mm f/1.7 is notorious for this problem. It's caused by bits breaking off the inside of the aperture ring (which is made of brittle plastic) and getting stuck, preventing the ring from moving properly.

It's not worth fixing. The only thing I can suggest is keep trying to move it and if you can get it into A mode and leave it there, it'll be fine for use on a DSLR.