# Thread: CCD to match Celestron 11" SCT?

1. ## CCD to match Celestron 11" SCT?

Good day

I am interested in getting a Celestron 11" SCT for minor planet
astrometry but need to decide on a CCD camera to match the telescope.

From the Minor Planet Centre, I got the following recommendation:

"You will need to know the focal length of your telescope and the
physical size of your CCD's pixels to calculate the pixel scale.
Your setup should be such that the pixel scale is no greater than 2"/
pixel (preferably) or 3"/pixel (at worst).

In practice, your optimal pixel scale is something that you will have
to determine for yourself, taking into consideration the capabilities
If your pixel scale is much larger than the values quoted above, then
the quality of the astrometry will suffer.
If your pixel scale is too low for your local setup, then the signal-
to-noise of the images may be low as each image is spread over a large
number of pixels."

I have found a calculator at

http://www.starlightccd.com/faq/ccdcalc.htm

to calculate the pixel scale for their products but what is the actual
formula?

The 11" Celestron has an aperture of 280 mm and a Focal Length of 2800
mm.

Which CCD cameras would you recommend? Which ones should I avoid? My
budget is limited to \$1500 but I could push it to \$2000 if I really
have to.

Thanks
Jack

2. ## CCD to match Celestron 11" SCT?

On Wed, 10 Jun 2009 06:36:27 -0700 (PDT), Jack

A = 206265 * d / F

where
A is the pixel scale in arcseconds;
d is the pixel pitch;
F is the telescope focal length (in the same units as d)

(206265 is the number of arcseconds per radian)

Thus, 2 arcsec = 206265 * d / 2800.

d = 27 um.

In other words, this telescope requires a large pixel camera to get your
desired scale of 2"/pixel. With typical science cameras having pixels
that are 9 um, you will be rather oversampled. That's actually not a big
problem for most astrometry, but you could easily reduce your focal
length. I'd look at using a 0.6x reducer (which will also produce a
flatter field). That will give you

A = 206265 * 0.009mm / 1680mm = 1.1 arcsec/pixel.

That's a very nice imaging scale, and depending on your target you can
opt to bin 2x2 to get 2.2 arcsec/pixel. Of course, it also means you
have a larger FOV than using the native focal length of your scope.

That is a very limiting budget for a good science camera. Avoid any
camera with a color sensor, avoid any camera that isn't cooled, avoid
any camera that can't take long exposures, avoid any camera without a
mechanical shutter. Cameras with full frame sensors will generally give
better results than cameras with interline sensors, although you can get
good results with either. Sensors with deep pixels (high dynamic range)
are often useful for astrometry and photometry, since this allows you to
have fewer saturated reference stars to compare with your (usually dim)
target.

Take a look at the SBIG ST402, or the ST7 if you need self guiding.
These are very good cameras for what you're interested in. The only down
side is that the sensors are rather small, which means you will have
fewer reference objects in the field than you might want.
_________________________________________________

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

3. ## CCD to match Celestron 11" SCT?

> That is a very limiting budget for a good science camera.

For a total of \$3000, which SBIG CCD would you recommend as a third
option using the setup as described and with a Focal Reducer?

4. ## CCD to match Celestron 11" SCT?

Hi Jack,

For a number of years, I've used an SBIG ST9-E camera on a Meade 12"
LX200 at F6.3, for minor planet astrometry. It's an almost perfect
match, with the camera's 20-micron pixels giving an image scale of
2.18 arc-seconds/pixel. It has a very high "Full Well Capacity" of
150,000 e-, which "cuts down" on the number of saturated stars per
image. You can find a used parallel port model for about \$1,000 on the
used astronomy equipment sites. Also, contrary to popular belief, the
camera is capable of taking beautiful deep-sky images ... using the
proper image processing techniques. Check-out this image of NGC 4565 I
took with this camera a few weeks ago:

http://www.geocities.com/jdilapo/NGC...5B25_final.jpg

Good Luck,

Jim

On Jun 10, 9:36 am, Jack <newsgroupread...@gmail.com> wrote: