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08-08-2009, 07:24 AM   #16

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QuoteOriginally posted by Marc Sabatella Quote
Yes, but have you actually tested for this effect? It could well be SR has been reduced to zero effectiveness (or worse) and you've just never noticed. If in controlled testing you have demonstrated that while setting SR focal length to 200 reduces the effectiveness of SR compared to setting it correctly, but that it does not actually make SR counterproductive, then great. I'm honestly curious, and would love to see test shots to document just how much of a difference it makes in situations like this.

I *have* tested it, and know for a fact the effect is real, but I admit I don't know how far you have to be off in order for it to actually be detrimental as opposed to simply reducing effectiveness. Like I said, the effect is extreme and obvious if you have it set for 200 when the actual focal length is 28. The only question is at what point does the effectiveness of SR drop to zero and start to become counterproductive. Could be when you are off by 2X, 3X, 4X, or something else - would be interesting to find out. But my money is on 2X.

They tell you to set the correct focal length; just because they don't spell out the consequences of not doing so doesn't mean anything. They don't spell out the consequences of doing a lot of things they tell you not to do.

As I said, they *do* tell you to set FL correctly; they just aren't explicit about the reasons. So even without giving a reason, they'll told you what you are supposed to do. Whereas, without this warning, how you would you know you were supposed to turn SR off when on a tripod?

Anyhow, we can theorized all we like; the proof is in actual tests. Mine have proved absolutely conclusively that the effect is real; the only question is how far you have to be off before it's makes SR counterproductive. Only testing would tell us for sure.

08-09-2009, 11:26 AM   #17
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QuoteOriginally posted by Marc Sabatella Quote
I too remember nothing in any Pentax manual about entering the longest focal length. And I can absolutely verify from experience that inputting too long a focal length can produce images that are obviously much worse than not using SR at all. But not if you only overstate focal length by a little - you have to be off by a lot before it makes matters worse. Entering 200 when you are really shooting at 50 would probably count, but I've noticed it primarily when entering 200 if I am actually shooting at 28. Entering 200 if you are really at 150 would probably be fine - although not as good as actually entering 150.

Of course, as far as I know, there are no 50-200 manual lenses out there - the 50-200's from Pentax are all AF and communicate focal length automatically.

Also, the topic of using older lenses on a DSLR comes up maube 3-4 times a week. i recommend browsing the forums for other discussions of the topic, including references to how to make the aperture ring work with a DLSR, and the change in field of view you will see when using a lens on digital versus film (aka "crop factor").
Tokina made a 50-250 f 4-5.6 AT-X lens; there was also a Sigma 50-200, 55-200, and others (Sakar, Soligor). A good listing of manual focus PK lenses is here (Bigma is on the list too for some reason, but that would communicate data to the camera): 35 mm MF zoom lenses

QuoteOriginally posted by billtin59 Quote
After actually looking this up in the K20 manual, pg 67, (as opposed to using my memory), it says "When using a zoom lens, select the actual focal length at the zoom setting in the same manner." It also goes on to explain that shooting distance influences SR as well. I suppose you could take this to mean when the lens is zoomed all the way (my initial interpretation), or you could take it as meaning whatever focal length you happen to be shooting at the moment, which seems impractical at best, and defeats the purpose of a zoom somewhat, don't ya think??

I have an old 80 - 200 zoom, and I input "200" and haven't had any problems at any focal length. to me, using the longer end covers you no matter where you are in the zoom range.
I seem to remember that chipped lenses "read" the make-believe "conversion factor" focal length as opposed to actual. I don't have any of the new lenses, so I can't verify this, but you might be getting away with a "200" SR setting because the camera (if the lens were "chipped") would assume it's a 120-300 as opposed to an 80-200. Anyone care to verify with a DA zoom?

QuoteOriginally posted by Marc Sabatella Quote
It's not that setting to 200 "covers" yu if shooting at 80 - it's that it actually causes the sensor to *overcompensate*. I'm not sure if it would do so enough to to make the image worse than turning off SR, but it would probably come very close; if nothing else, it probably cancels out most if not all the advantage SR would otherwise have given you at 80. Try some tests with and withlout SR while shooting at 80 versus at 200. If you have the SR focal length set to 200, my guess is that you'll see SR giving a lot of improvement when actually shooting at 200, but not when shooting at 80.

And yes, you're right, it makes shooting manual zooms with SR a pain, which is why I don't bother buying manual zooms. But for those who do, better results would probably be obtained setting SR somewhere in the middle of the range - so that it doesn't overcompensate *too* badly at 80, and some compensation at 200 is better than none. Either that or set SR to 200 on the assumption that you'll most be using it at that end, but if you find yourself shooting at 80, you might be better off simply turning SR off.
Shooting with manual zooms is a snap, just like it always has been. Simply turn SR to "off," mount your camera/lens to your tripod and shoot, thereby giving you better than shake "reduction" - you get shake "elimination."
08-09-2009, 01:49 PM   #18
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QuoteOriginally posted by 24X36NOW Quote
Shooting with manual zooms is a snap, just like it always has been. Simply turn SR to "off," mount your camera/lens to your tripod and shoot, thereby giving you better than shake "reduction" - you get shake "elimination."
True enough - but completely impractical in most of the situations where I would want such a lens.

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