couple questions on the 70-200 IS 2.8L

[clkgtr37]

I have been experimenting with my 70-200 IS and have found a few thinns I wasn't expecting. Is this lens (as with almost every other lens) a little bit softer @ 2.8 than say @ 8? Also when shooting, does the rule of thumb, "when hand holding, shoot at a shutter speed equal to or higher than your focal length" apply to this lens? I've heard two answers:
1) IS will let you get crisp pictures down to 1/15 of a second
2) IS only means that your pictures will be sharper at 1/200, not that you can shoot below 1/200

[Pekka]

clkgtr37 wrote:
I have been experimenting with my 70-200 IS and have found a few thinns I wasn't expecting. Is this lens (as with almost every other lens) a little bit softer @ 2.8 than say @ 8?

That is normal. around 8 it is always shapest and up and down from that it will get unsharper a little. Good lenses show that phenomemon less, but all do. People pay for lenses like 70-200 in order to have less of that effect.

Also when shooting, does the rule of thumb, "when hand holding, shoot at a shutter speed equal to or higher than your focal length" apply to this lens? I've heard two answers:
1) IS will let you get crisp pictures down to 1/15 of a second
2) IS only means that your pictures will be sharper at 1/200, not that you can shoot below 1/200

2 is partially correct. If 1 is correct depends on focal lenght and holding stability in the first place:

IS does not stop movement, so if you shoot e.g. moving people with 1/15 it will get blurry. IS is good for stills, in dim days and when long focal lenghts are used. But you can do the same if you put ISO higher...

The rule of thumb you referred to has to be matched to digital era. In D30 and D60 the rule goes: basic handhold shutter speed is (1.6 x focal lenght in use). Also, this rule is for normal size prints only, when you print larger you will have to get more shutter speed or produce less vibration (tripod, monopod).

[Roger_Cavanagh]

This is what Canon says about IS:

Canon sought to remedy this with the world's first SLR lens with a built-in image stabilizer. In response to the angle of the lens' optical shake, the compensating optical system (gyro unit and shifting optical system) moves in parallel to cancel out the shake. The result is equivalent to using a shutter speed two stops faster.

So using the focal length rule of thumb (updated for the D30/60), minimum handheld shutter speeds would be at 70mm:

70 x 1.6 = 105
say 1/100 sec
2 stops faster = 1/25 => 1/30 second

At 200mm:

200 x 1.6 = 320
2 stops faster = 1/80 => 1/90 second

Regards,