Quote Originally Posted by donnman


Thanks Dallas...you are correct, I am confused about what IS actually will help with. So basically it will help me create a steadier hand for my shots, so to speak. Using a tripod or in some cases even a monopod, I probably wont see much if any difference. But is with the hand held shots, maybe walking or strong wind, whatever makes my hand unsteady, this is where I will see improved results.
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The longer (more telephoto) the lens, the faster you'll need the shutter speed to avoid shake blur. Sometimes, the only answer to that problem is aperture. I tell people to look at their pictures and assess what's blurry - if the whole picture is blurry, IS might be the answer; if the subject is blurry, wider aperture (or higher ISO) is more likely the answer.


From a mathematical perspective, normal rule of thumb for handholding is 1/&lt;effective-focal-length&gt; (where EFL is lens focal length x camera crop factor). With a 2-stop IS unit (first generation), this becomes 4/EFL. 3-stop IS unit becomes 8/EFL, and the newest 4-stop IS units become 16/EFL as the rule of thumb. A 70-200 lens is somewhat in the middle - on a crop camera, 1/320th might be doable except in low light, but a 400/5.6 (at 1/640th) ends up with a handhold "requirement" faster than typical stop-action needs.