Re: Meade DSI pro versus firewire webcam for planetary use?

On Fri, 27 May 2005 01:45:07 GMT, "Bob Fields" <fieldsbob@xxxxxxxx>
wrote:

>As a fellow planetary imager who has been using standard Toucams for years,
>my mind is opening up to the possibility of upgrading my system to either
>one of the new firewire type cameras, basically offering uncompressed
>captures at higher frame rates, or the Meade DSI pro (please forgive me on
>the latter if I don't have the name correct: I'm referring to the new 16
>bit Meade monochrome non-peltier camera).

My understanding is that the DSI is optimized for long exposures, so it
is not going to be as good as a webcam for planetary imaging, where you
want very short exposures.

> I'm really wondering which
>upgrade would be best because in the firewire's case, we are able to capture
>many more frames of 8 bit quality and stack them... but the fact remains
>that the original frames are still 8 bit meaning more frames would have to
>be stacked to increase the dynamic range of the image than in the 16 bit
>camera's case. Am I correct? I'm assuming that the 16 bit would require
>less frames for stacking to both overcome noise and increase dynamic range.

For planetary imaging, the difference between 8 and 16 bits is generally
unimportant. That's because you are photon limited: during the short
exposure you need to freeze the seeing, you don't get enough light
(above the readout noise) to give you more than 8-bit dynamic range
anyway. Put another way, an 8-bit and a 16-bit camera would both give
you, say, 200 counts in the brightest part of Jupiter, and 10 counts of
noise. It doesn't matter if those counts are packed in an 8-bit or a
16-bit word- the result is the same, and the number of frames you need
to stack for a given S/N are the same.


>So, I can't make up my mind. I've seen a good many excellent images of
>planets with conventional CCD cameras, but these fps rates are even slower
>than the Meade's so I think the process is much tougher... but then again
>only 15-20 frames appear to be sufficient.

It depends on your seeing. Where I am, I need several hundred frames for
really good results. Under very steady skies, you can use fewer frames
with longer exposures.


>Suggestions would be appreciated.

Unless you are imaging under extremely good conditions (for example, the
Gulf Coast), I think you'll get better results with a webcam.

_________________________________________________

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

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