Ruined said:
(1)If you are using an appropriate shutter speed (reciprocal of focal length on full frame, reciprocal of focal length*1.6 on crop) then IS basically does nothing. So, to give an example, if you are using a 50mm lens, a shutter speed of about 1/50 or faster will result in no camera shake and no benefit from image stabilization.
(2)Again, the slower your shutter speed the more moving objects blur, which IS cannot counteract. And, with my own testing I further noticed that once you start to get real slow shutter speeds handheld everything starts to look mushy even when it is within the range of IS to correct.
(3)When do you need a slower shutter speed? When you don't get enough light.
1. The "reciprocal rule" is a rule of thumb. If after the "best we can do", sometimes a rule of gnat's a## is preferable, if available.
Consider this challenge - mount a 50mm lens, in plenty of light, shoot at 1/50, and see if you can shake the camera as you press the button enough to create a less sharp than desired image.
if you agree that this can be done, then we are talking about the degree of shake applied at the camera. if you think that it will not exceed the arbitrary standard-shake which the "rule" will cover, I imagine you to be free of any of the tremor that, in varying degree, effects many an older photographer, and that you do not hurry up inclines or across distance to change position relative to moving subjects(wildlife), and therefore are not ever shooting winded or tired (or old) enough to be shaky.
2. If the subject is immobile, the focus is correct,and the photo is still mushy, then the camera shake is patently NOT "within the range of IS to correct". The amount of correction available is finite, and can be inadequate if more is required than available.
3. I have plenty of light. I WANT the moving-object blur (which the IS "cannot correct"), and I want surrounding subject area Pin-sharp (which IS can help provide). The subject is a waterfall. Other situations could be imagined.
The amazing difference in what can be "seen" with binoculars, and what can be "studied" in detail with stabilized binoculars provides a clear example at human viewing speeds (vs a split second shutter ) of how helpful IS can be in countering human-induced camera(or binocular) shake.
I have posted a number of times elsewhere a link to a German photographer (name escapes my aging grasp ;-) ...Polking?) who has tested IS and "sharpness" extensively. His (and my) conclusions - If you are after the absolute best you can get, use every technique and piece of equipment available to steady the lens/camera when the shot is taken ( Tripod, weights, lens AND camera supported, IS (if tripod compatible), wind-shield, remote release (preferably wireless) etc.
Unless you have a granite tripod, an absolutely steady, smooth touch on the button, no wind, etc., SOME degree of quality in the image is likely to be lost when compared to what might-have-been.
This is , of course, perfectionist territory, and to whatever degree one is satisfied with less, the above considerations can be ignored, and "rues of thumb" substituted.
But they can hardly be considered "plenty good enough" for one and all. They are often as much gossip as gospel. ;-)
