Re: Why .avi format ?

On 29 Nov 2005 00:38:24 -0800, "atasselli@xxxxxxxxxxx"
<atasselli@xxxxxxxxxxx> wrote:

>True. But webcams are really the lower end of the video imaging
>spectrum.

Yes, but even most high quality video cameras have high readout noise.
It is intrinsic to the CCD sensors available, and cheap electronics just
adds to it.


>I opine that while it is true that longer exposures will produce higher
>S/N images (with the same length of time) it is not true that they are
>going to be necessarily better. If the subject being imaged is bright
>(relative to the scope/camera combination at hand) shorter exposures
>(30s-60s) will go a great length in improving resolution, if you
>haven't got a tip-tilt AO.

Interesting. Different people report different results here, so I think
it has a lot to do with the specific details of your local seeing. I've
made thousands of seeing measurements, looking at the frequency spectrum
of the shift, and for me, the short exposure advantage ends at about one
second. That is, I'll see reduced star sizes up to about one second, but
no difference between star sizes for longer exposures.


> There is also the problem with
>oversaturation of bright stars in the field that can be worked around.

This is the usual reason I will choose to shoot short exposures. It
costs me in noise, but keeps all my data linear. Of course, a decision
like this depends also on the ultimate intent in collecting the data.


>As you said, cool stuff. Are they available commercially?

Not really. A few very specialized (non astronomical) cameras using the
sensors are available, but are extremely expensive. The sensors
themselves are available (or were a few years ago) as engineering
samples, but you need to make your own camera around them. The one I
have has lots of problems- dead columns, hot pixels, and the like, so I
don't use it for more than testing. If they ever get the bugs worked out
of the technology, and these sensors become common, it will
revolutionize astroimaging.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
.

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