Sorry, excuse the cheesy title. I know what IS means and what the benefits are but then I occasionaly see people referring to certain lenses that come as IS and non IS and they say the non IS version has better IQ?! How? Surely the entire point of IS is to improve the image quality? ALSO, why do people say to turn IS off in certain circumstances (i.e. with a tripod)? I mean I can see why the IS might not be needed there but why actively turn it off?
P.S. On that note what the hell is IQ anyway? Is there a specific measure of image quality that can be compared or is it all in the eye of the beholder?
IS is a completely brilliant invention. I can't think of a single reason why anyone should not want it, apart possibly from the potential cost. But actually, there are very few lenses available as either IS or non-IS versions and while they might appear to have a similar spec, they are actually completely different designs. You can't really compare them directly.
A couple of examples. Canon's 70-200L zooms are available in various configurations, and in all cases the the IS versions have better IQ. Tamron's 17-50 is available with and without IS and the IS version is reputed to be not as good. But then again, in all these cases the optical designs are compelety different :shrug: By the way, IQ means image quality of course and can include a lot of things, but most people use it as shorthand for sharpness and/or noise.
With most modern lenses you can leave IS on with a tripod. Some you can't, like the popular Canon 100-400L which has an old version of IS and the image 'drifts' when on a tripod. It's a feedback loop between the gyros and the motors.
There is also an argument that says IS can add blur to an image at very high shutter speeds. This comes particularly from Nikon users and there are lots of lengthy internet threads about at. All of them are lacking any pictorial evidence; it's a theory that doesn't stack up IMHO. Likewise, IS said to affect bokeh - really? How? Why? Just another theory from the purist Luddites
Actually, I would say the opposite, and I have seen clear evidence of IS helping at much higher shutter speeds than the hand-holding 'rule' suggests, especially if you are a bit shaky or really want to get the last drop of sharpness out of a high pixels sensor. Camera shake doesn't just disappear at higher shutter speeds, it is merely reduced to an acceptable level, and from my own testing, IS always raises that level.
Another thing, in-lens stabilisation also steadies the viewfinder image which is a real help when framing with long lenses. In-camera stabilisation doesn't do this.
... this is entirely possible. I don't understand the mechanism of IS, my understanding was that it tries to compensate for camera shake and thus can give you an extra stop or so if handheld but I couldn't see why this would have any negative effects.
? I guess I just assumed that the system would be intelligent enough to compensate the shake relative to how much was actually needed but without knowing how it actually works I guess that might not be easy/possible.
