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11-20-2009, 04:29 AM   #1
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Pentax DSLR with analogue Lenses: A question!

Hey people,

I have a Pentax K-m and I'm using my good old analogue Telezoom (28-80mm).
When I mount the tele on the K-m and switch "on" it always asks me to set the focal length. Should I set it to the lowest (it think it would be 30mm or 25mm there) or to the highest? Or to an average value?
I've been always going with the setting "75mm" (since there is no "80mm"). Went pretty good but I don't no if it (when wrong set) interferes with the focus or some other function.
I have, obviously, the same problem with my other old tele (80mm-200mm).

Thanks!
Rieby

11-20-2009, 05:18 AM   #2
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An educated guess would be that the SR "overcompensates" if you have a higher focal length in-camera than set on the lens.
The most safe (no overcompensation) approach would be to set the SR to 28mm, of course, but if we consider SR comensation a linear response, it would probably not degrade the image quality too much if you set it at e.g. 50mm.
However, following some degree of logic, SR@75mm and FL=28mm, the more the SR has to compensate (longer shutter speed and/or more shaking), the more "overcompensation" you get.

My 50mm prime gets quite allright results even when the SR is set to 75mm and shutter speed is ~1/20". Images with SR set at 400mm turned out quite blurry at shutter speeds ~ 1/40". However, this is not a scientific approach, of course.
11-20-2009, 05:24 AM   #3
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I have a similar problem with a manual 70-210. I tend to set SR as close to what I expect to be shooting at as possible... as that's usually the longer end I set it to 200mm more often than not. If I do change the length drastically I just switch off and on and change it accordingly. It's a bit of a nuisance, but worth the hassles in exchange for a working, stabilised lens.
11-20-2009, 12:25 PM   #4
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For the sake of convenience, set your SR to the shortest focal length on the zoom. The SR will still work just fine, but you don't have the possibility of shake reduction induced blur.

11-23-2009, 02:18 AM   #5
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QuoteOriginally posted by Wheatfield Quote
For the sake of convenience, set your SR to the shortest focal length on the zoom. The SR will still work just fine, but you don't have the possibility of shake reduction induced blur.
Thanks for the hint Wheatfield, would certainly save me much trouble (and the on/off much wear and tear). Do you know why it works? I mean surely SR set to 70mm shouldn't work when the lens is around 200mm?
11-23-2009, 12:56 PM   #6
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It works some, just not as well. It still detects the shake, it just just doens't correct for it as completely. Whereas srtitng 200 but shooting at 70 results in overcorrection, and too muh of that *can* ruin an otherwise good photo (although I've only personally experienced this when setting 200 for the FL but actually shooting at 28 - a more extreme difference). Feel free to experiment - everyone's results will probably vary - but I'd personally start by assuming something around 100mm might make sense. Not so much above 70 to cause problems, not so far below 200 to make it worthless. Or else i'd set it to 200 but turn it off when shooting at 70. Mostly, I consider this just another reason to avoid manual zooms.
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