I understand what IS does, but what does it exactly buy you in terms of shutter speed? Do I get the same effect as a non-IS lens at 1/50 sec if I use an IS lens of the same focal length at 1/25? Is there a rule of thumb?
Depends on the IS. The IBS of the E-P1 sometimes gets me an extra stop or two, by whichever way you want to get it, but sometimes I'm calm enough to get better pictures without it. I had a play with the OIS in the 45-200mm Panasonic zoom lens, and it easily got me an extra two stops, meaning I could use a lower ISO, a faster shutter or a smaller aperture. It's better for me than the Olympus IBS, but it's not available to all lenses. Your best bet is to play. It's amazing how patient the guys in camera shops when you're testing lenses out; they love to see them too!
Just a quick example of the in-body stabilisation of the Olympus E-P1. The lens was 50mm, at f/1.7. The ISO was set to 800, and the only light source from this side was the bathroom door on the other side of the house, which you can see reflected in the cat's eyes. The street outside is lit by street lamps and a pub. I held the camera still for half a second whilst lying on my back, with my elbows on the mattress of our bed (I needed extra distance, and the bed was behind me, so back I went...) This would not have been possible without the IS being on. I also used 1/8" ant-shock, which is a big help.
well if you believe dpreview... Olympus E-P1 Review: 13. Performance: Digital Photography Review at the bottom of that page is their tests with and with out IS for the e-p1. It alleges that 1/125 with out IS = 1/30 with IS. You could probably find similar charts on the panasonic cameras with IS lenses on dpreview.
Thanks - I will look there. As much as I like my GF1 if I can get shutter speed improvements like that it could be beneficial for for my tele and macro shooting (since they are adapted lenses) to replace my GF1 with an Oly (or add an Oly).
