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06-09-2011, 06:35 AM   #1
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D FA 100/2.8 WR owners: problem?

I received a "used" but essentially new copy of this lens yesterday. As always when I get a new lens, I inspected it carefully, and tested the aperture mechanism by hand. When I move the lever to open the aperture up fully, the spring feels a little weak compared to all of my other Pentax lenses, and when I let go of it, the aperture closes, but doesn't seem to have the same "snap" that I expect. Rather being effectively instantaneous, it seems like I can almost see it get smaller as it closes. In other words, it feels sticky, like I would expect from an older lens with lots of oil on the blades. The lens, however, is pristine, and I have carefully inspected the blades from both sides during slow opening and closing.

If it were sticky, I would expect overexposure at small apertures, and possibly inconsistent exposures, so I did the obvious tests, and here's what I found: at any aperture other than wide open, there is a slight overexposure, maybe a quarter of a stop or so. This amount of over exposure is consistent at all apertures smaller than f/2.8. I then did 10 consecutive shots (single shots, not rapid fire) at f/8. No variation in exposure at all. I did the same thing at f/16, f/22, and f/32, with the same results. So the lens seems to function perfectly normally, with the exception of the very small but consistent overexposure when not wide open.

This is something I can live with, not a problem at all. I'd say the overall condition of the lens is 100%, and the functionality is 99%. But I worry about the "mushiness" of the aperture spring, and whether it means I could expect problems in the future. I don't know what to do about this, if anything. The person I got it from is someone I have dealt with a few times before, a great guy, and I have no worries about him helping me deal with the problem. I believe he is the original buyer, and can deal directly with warranty claims. But it's a pain in the butt, and I'd love to just start shooting with the lens. I guess I'm trying to weigh the likelihood of future trouble against the normal variation in quality control that seems to be the rule these days with all manufacturers. Maybe Pentax would replace the lens, but maybe the replacement would have another issue.

Whaddya y'all think? Am I being too cautious? Can anyone speak to the firmness of the aperture spring in this lens, compared to other lenses? Maybe this is completely normal.

06-09-2011, 06:59 PM   #2
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Checked mine and ...

Hi Todd,

Pulled out my other lens to compare, Da18-55mm kit lens, S-M-C 50f1.4, Da 40 and Da 12-24.
For what it's worth, my copy does not show any signs of being sticky, snappy just like the others. Lined up the modern lenses side by side, used my index finger, flicked and felt the tension of the aperture lever spring. I can feel some tension difference, 12-24 and 40 are the same and firmer (spring tension) than the 18-55&100mm. But overall still snappy.

What I did notice was that the 100mm WR, when it snaps it does sounds tinny compared to the others, which i put down to the lighter longer hollow feel metal barrel. The SMC 50F1.4 needless to say sounded fast, firm and solid.

Not scientific but hope it helps.

Cheers

Ken
06-09-2011, 07:33 PM   #3
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My copy of 100mm WR has a very snappy aperture lever spring — as snappy as any of my lenses, snappier, even, than the DA 10-17 and the DA* 300. Given that there are over-exposure issues in addition suggests there might be a problem which could get worse over time. At $600+, it's not exactly an inexpensive lens. It shouldn't have that problem and I would get it repaired/replaced while that's still possible.
06-09-2011, 07:38 PM   #4
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I got mine yesterday, new. It's real snappy.

06-10-2011, 12:05 PM   #5
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Thanks you guys for checking your lenses for me. I guess this thing should probably be sent in for repair or replacement.
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