I've been rethinking his comments about shutter speed. The statement
essentially said that, above the flash synch speed, the sensor is never
fully exposed due to the shutter being a traveling slit. As the speed
approaches the sampling frequency it becomes more and more likely that
the image strip exposed by the slit at sampling position B are not the
same as position B *was* when the exposure was made at position A. In
other words, at higher speeds there's a greater probability for blur
since each part of the sensor can see slightly different parts of the
image at different times... um, well, yeah... that's the definition of
what causes blurring whether over the full sensor or just part of it.
After rethinking this I've come to the conclusion that this is
absolutely true but... meaningless with respect to shutter speed.
Irrespective of the IS system's sampling speed (relative to shutter
speed) the IS system's ability to compensate for camera motion is
exactly the same whether the shutter speed is 1/60 second or 1/4000
second. So it remains true that a 1/4000 second exposure will show less
blur than a 1/60 second exposure. Whether or not the IS system is truly
effective at 1/4000 second will be dependent on the sampling and
response frequency of the system. But regardless, the 1/4000 second
exposure will have less blur than the 1/60 second exposure whether the
IS system is fully compensating or not. It can only make it better but
not worse.
Thinking further, maybe the IS system should be left on when on a
tripod. The camera on a tripod is still subject to ground vibrations and
shutter/aperture vibrations. Maybe the IS system can compensate for
these as well. If not, a smart system shouldn't make it worse.
Chuck Norcutt
On 11/10/2012 7:36 PM, Moose wrote:
> It's impossible to know about sampling frequency without knowing what it is
> on various IS systems. Most of the rest
> either doesn't apply, we already know or is common sense.
>
<snip>
>
> My conclusion? Forgetting to turn off E-M5 IS on a tripod isn't such a bad
> thing. The E-M5, six axis IS system is quite
> different from both 4/3 and preceding µ4/3 cameras, so I don't believe my
> result is generalizable.
>
> As to turning it off for higher shutter speeds, I don't know. I would have a
> problem with that in the field. One of my
> lenses goes out to 600 mm eq., which I use not infrequently. That requires
> 1/600 without IS, more, really, with the
> ability to pixel peep if one might crop or print large.
--
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