Re: Why .avi format ?


Chris L Peterson wrote:
> On Sun, 27 Nov 2005 20:58:48 -0500, Tom Rauschenbach
> <tomsusenet@xxxxxxxxxxxxxx> wrote:
>
<snip>
>
> There is only one fundamental benefit of short exposures- the ability to
> capture images during brief moments of atmospheric stability. A
> collection of many images can be graded for quality and the bad ones
> discarded. This is functionally equivalent to high order adaptive
> optics.

Not really. High order adaptive optics allow to correct the exit pupil
phase differences while select-and-stack simply rejects those that do
not qualify. If time is important (and it IS important in planetary
imaging as the planets rotate) and the resolution is high, video
imaging does not even come close to the perfomance (theoretically)
achieveable with adaptive optics. The only real good thing of video
imaging is that it can operate in the visibile without any restriction
(except for coherence angle, of course). And, yes, it is immensely


>Readout noise makes for a stiff noise penalty, but with hundreds
> or thousands of images the noise is substantially reduced. But the
> technique is only useful for very bright objects- the Sun, Moon, and a
> few planets.

This depends on the read-out noise. The lower it is the less different
the 2 techniques are.

>
> Once you start imaging DSOs, you need long exposures- many minutes is
> usually required to maximize S/N.

Not really. I've been imaging DSOs for the past 4 years without ever
taking exposures longer than 120s, 45s to 60s being the most common
durations. With low read-out noise camera there are benefits in using
short exposures.

Regards

Andrea T.

.

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