Image Scale - how is it calculated?

Folks - how is image scal calculated?

I've always only ever used Ron Wodaski's visual basic program... :oops:

Covington's "Astrophotography for the Amateur" gives the following formula:

Field of View in arcseconds = (206265 x CCD size in mm) / scope focal length in mm

Example:
TC-255 CCD is 2.4mm x 3.3mm
20cm f/10 scope focal length = 2000mm
Field of View on CCD = 247" x 340"


Pixels per arcsecond = (206265 x pixel size in mm) / scope focal length in mm

Example:
TC-255 CCD has 10micron pixels. 10microns = 0.01mm
20cm f/10 scope focal length = 2000mm
206265 x 0.01 / 2000 = 1.03 pixels per arcsecond.

Phil.

Dave,

Nice easy formula I use;

Pixel scale = (206,265 arcseconds x pixel size) / focal length

e.g, focal length 1000mm, pixel size 6.4microns

(206265 x .0064) / 1000 = 1.32 ArcSecs per pixel

Hey Phil Snap!

Pixel scale = (206,265 arcseconds x pixel size) / focal length

Dave,

This is the formula I use as well and which I have committed to memory ... I work with 1.27"/pixel using my AP160 and ST-2000XM.

With my 10" reflector and ATIK 16HR I get 1.33 arcsecs/pixel, with my 80mm refractor its 2.75secs/pix.

With that formula its easy for someone considering a scope camera combo to get close to the magic 2'/pix. e.g. for an ATIK 16HR the optimum focal length is 660mm or for a 500mm refractor the ideal pixel size is 4.8uM.