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Old 22-05-2005, 12:07 PM
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CometGuy
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Join Date: Feb 2005
Location: Brisbane
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Tony,

Most of the SAC cameras seem more suitable as planetary imagers. This is because most of the cameras have small sensors but are capable of high frame rates (i.e video output). They would also make good autoguiders.

For deepsky I think the 16bit, cooled monochrome SAC 10 cameras look excellent value especially if you are imaging small DSO's where maximum sensitivity is require. The biggest issue is the small field of view of these cameras, which may or may not be a problem depending on the application. Some of the offered sensors have pixels so small you will almost certainly want to do in-camera binning. I would avoid the 3.3 MPixel one-shot colour camera for this reason (because you cant easily to in camera binning).

When it comes to one shot colour cameras I think a DSLR offers excellent performance vs cost. The advantage with a DSLR is you get a big sensor with relatively large pixels (read sensitive) and this gives you a lot more flexibility in what you can image. As you may know the biggest disadvantages of DSLRs is the strong IR Cut filters that severely effect red response, but green/blue response is still excellent. However it is possible to modify the camera or buy a modified camera to drastically improve red sensitivity. Note that Hutech are selling a 350D with transparent window (so AF still works) for $1350 US that with a $70 external (MaxMax Colour correction) filter can be used normally as daylight camera as well.

Here are some comparison shots I made of M83 between a cooled astrocam (equivalent to an Sbig ST-7E), a standard 300D and modified 300D. You will note there is not much difference here pre/post 300D modification, partly because the sky background was a lot brighter and partly because this object has a lot of blue. The astrocam reaches about another magnitude deeper for the same exposure.

http://www.pbase.com/terrylovejoy/image/34613663

Is there anything I don't like about DSLRS? Yes..the IR Cut filter which I spoke of above. The lack of cooling also reduces image quality slightly in summer, it also requires a little bit more attention when doing dark frame subtraction. Lastly, something you will see weak banding in the image background. This banding I think is caused by the tremendous speed at which the cameras read the images (i.e 64 million pixels/second for the Canon Pro DLSRS). A dedicated astrocam reads out the sensor slower so you tend to get a very smooth even background.

Lastly, how does a DSLR perform in light polluted skies. Here is a 9 minute exposure (6 x 90 second) of Omega Centauri taken during a near full moon.:

http://www.pbase.com/terrylovejoy/image/42439418


Terry
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