Tests of IS on Canon 75-300 IS

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Tumbleweed - 30 Mar 2005 13:14 GMT

I've just been idly taking some comparison shots with a Canon 75-300 IS,
with and without stabiliser switched on.
The results surprised me so much I repeated them several times to be sure.

I used the lens at full telephoto on a 300D
The "effective" length in 35mm FoV terms would be 480, so I would expect to
need a shutter speed of 1/500.

Speed 1/500 no IS : image slightly soft
Speed 1/500 + IS : image pin sharp
Speed 1/250 no IS : image soft
Speed 1/250 + IS : image pin sharp
Speed 1/160 no IS : image soft
Speed 1/160 + IS : image pin sharp
Speed 1/100 no IS : image soft
Speed 1/100 + IS : image soft, visible double image, IS is worse ****
Speed 1/60 no IS : image unusable, bad shake
Speed 1/60 + IS : image shaky, smeared double image, IS is worse****

The conclusion I have to reach is that with "my" lens I get a marked
improvement at the appropriate shutter speed and up to 2 stops down, but
beyond that the image is actually WORSE with IS selected.

(I must point out that these results are only relevant to this one sample -
I haven't tried any other IS lens.)

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Alan Browne - 30 Mar 2005 15:38 GMT

> I've just been idly taking some comparison shots with a Canon 75-300 IS,
> with and without stabiliser switched on.
> The results surprised me so much I repeated them several times to be sure.

IS shots can vary greatly from frame to frame at the limit of
performance. IS is not an excuse to be sloppy. Best practice posture,
holding technique and gentle shutter release will get the best results.

The photo mags base their IS/VR/AS tests on hundreds of photo tests as
they know that from frame to frame, the photog has variance in his
movements.

Cheers,
Alan.

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Charles Schuler - 30 Mar 2005 23:09 GMT

> The conclusion I have to reach is that with "my" lens I get a marked
> improvement at the appropriate shutter speed and up to 2 stops down, but
> beyond that the image is actually WORSE with IS selected.

IS adds its own form of shake. It's called noise. That's why you are
supposed to turn IS off when using a tripod.

IS is a negative feedback system. When there is "external" shake, IS might
cancel much of it and that's great. However, with no external shake and IS
switched on, there is always going to be some electrical noise in the
sensors and in the servo amplifiers. This noise is sent to the moving lens
element actuators, which causes a touch of blur.

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