Re: CCD misunderstanding/ confusion
- From: Chris L Peterson <clp@xxxxxxxxxxxxxxxxxx>
- Date: Thu, 21 Apr 2005 05:07:40 GMT
On Thu, 21 Apr 2005 04:59:11 GMT, "John Edmund" <12345@xxxxxxx> wrote:
>There's something I think I have wrong concerning CCDs and I wanted to find
>out the correct answers. Say I have a webcam, which has an ICX098 CCD and
>another camera with an ICX424 CCD. I want to image Jupiter with a C8 and
>3x barlow ahead of the webcam and other camera. When the webcam/ barlow/ C8
>combo are used, let's say that the diameter of Jupiter on the laptop screen
>is 3" across. Now, I remove the webcam and replace with the camera with the
>ICX424 CCD, making sure the CCD is the same distance as the webcam's. What
>will the image size be on the screen now?
>
>The part I'm finding confusing is this: since the ICX424 covers a larger
>pixel area than the 098 and also has a larger pixel size(?), I am assuming
>the amplified Jupiter will not be the same size on the screen that the
>webcam produces, and in fact the image will be smaller. Am I wrong? Or is
>it that the 424 just covers a wider
>area and the image size of Jupiter is still the same?
Right the first time- the size of Jupiter on the screen will be smaller
when using the camera with the larger pixels.
>Finally, what benefit, if any, would there be with this combo system if
>using just the 424? Would there be better resolution than the 098 offers or
>worse?
Just because the pixel size of one of the cameras is smaller, that
doesn't necessarily mean the resolution will be better. That is because
something else may be what actually limits resolution- the optics,
seeing, etc. If the pixel scale is much smaller than the scale of the
seeing, the extra resolution is empty, and the small pixels will be
collecting fewer photons and may deliver poorer S/N.
Ultimately, what is important isn't the absolute size of the pixels, but
the pixel scale, which is determined by the pixel size and the telescope
focal length. Once the pixel scale is optimized (usually to a few tenths
of an arcsecond for planetary imaging), the size of the sensor simply
determines the field of view.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
.
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