Quote:
Originally Posted by jepsie
With auto-ISO, I take a shot of my Cornflakes box at ISO 1250. I manually adjust that down to ISO 250 and still get the ingredient list equaly sharp....
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A stop is a doubling of the light, or a doubling of the iso.
So, 1250 -> 625 -> 312, so you're getting just a little bit over 2 stops from the IS. That's typically what I find with the 24-105's IS: you can always count on two stops, but not necessarily more than that, despite marketing claims. So, whatever number the autoexposure gives you for iso, quarter it, and that's about where you want to be. With shutter speed, you can quadruple it (i.e., 1/100s -> 1/25) and you'll be ok. And with aperture, you can stop down two full stops and still be ok.
This is why we use a stop/EV as a measurement for exposure: you can swap it among the three main settings however you please.
So, in shutter speed terms, with the 1/focal_length rule, if you're shooting at 105mm, you want your shutter speed to be at 1/105s or faster. But with the IS turned on, that means you could go down to 105 -> 52 -> 26, so 1/25s or so is probably your handholding limit, shutter speed wise.
Sybren--for a lot of newbies, thinking in terms of ISO actually makes sense, because it's the single control you can easily grasp the effect of with P&S cameras, and it's the one control nearly everyone with a P&S uses.