View Full Version : A little help, please? (Telescope question)

2003-Nov-07, 01:11 AM
I need help with my homework. :oops:

I am given a telescope's aperture and its effective focal ratio, and the physical size and number of pixels of its CCD. I need to find the scale of the chip - arcseconds per pixel. I have a feeling that this is absurdly simple and I am missing something horribly obvious, but the longer I try to think about it, the more my head hurts. :-k

Help, somebody?

2003-Nov-07, 01:37 AM
For visual, the rule of thumb (iirc) is to divide the apparent FOV listed for a given eyepiece by your magnification to obtain "true" FOV. Since you have f/ratio and aperture, you can figure focal length of the scope (aperture X ratio). This will allow you to obtain magnification (focal length of the scope divided by focal length of the eyepiece).

There's an actual formula to figure the true FOV exactly, but it escapes me right now. Plus, not sure how this would apply to CCD's. So, basically, I guess I'm no help at all! Sorry

2003-Nov-07, 02:51 AM
Thanks for trying. That's all I'm able to find, either.

2003-Nov-07, 02:56 AM
Well since you did try, and the general consensus here is that the forum isn't a "homework help" place for quick answers:

CCD pixel size to arcminutes

General quick rule of thumb:

Divide pixel size (in microns) by the focal length (in mm), then multipy by 206. The answer is in arcminutes per pixel.

Proper formula:

ArcSec = 3600 * ARCTAN( (PixelWidth * 10^-6) / FL)

ArcSec = Width of Pixel in Arcseconds
PixelWidth = Width of CCD pixel in microns
FL = Objective focal length in meters

2003-Nov-07, 03:04 AM
Wow... great timing! Just as I came back to say I'd figured it out! :D

Thanks, though.

2003-Nov-07, 03:26 AM
Glad you found it.