Originally posted by RioRico Thanks for the answers, but what confuses me (because, duh, I haven't done any empirical tests, duh) is: the physical length of some lenses changes when you zoom in/out. I can understand that SR would need to accommodate a different physical length, like my Promaster-Tamron that stretches noticeably going from 60mm to 300mm. But the PA 70-210 under discussion doesn't change length. Front and rear elements remain in place; only interior elements move. I have a hard time grasping how SR handles such internal movement. Maybe there's a tech note somewhere (or maybe that's a trade secret).
And, an AHA! moment -- thinking about the above, I know now why some handheld macro shots have been disappointing, even with Catch-In-Focus. When my M42 90mm macro lens is fully extended to 1:1 magnification, it's now 180mm long. So I'd better reset the SR when it's stretched out. Bother...
Anyway, does anyone here have knowledge of how SR works, and whether the distinction between stretching and non-stretching zooms is significant? Or should that be asked in a new thread?
The physical length of the lens has not really anything to do with the SR setting. The Shake Reduction is dependent on the focal length. Thus, with a manual zoom lens, where the camera cannot read out the actual focal length of the lens and use that info for SR, you need to set an adequate fl manually.
On the other hand, it is clear, that the mechanical built of the lens (i.e. its length, weight and generally balance) will affect camera shake. For instance, you can still use the Bigma handheld at 500mm, but you can't really use the Pentax 500/4.5 handheld, because it is just too big. Such a difference between lenses will influence the effectiveness of SR, but cannot be set in the camera.
Ben