**FieldOfView**

## Calculating Field of View, etc.

CCD Calculators are fantastic since they shorten the amount of time youneed to

spending determining some value. However, if you have to wait for the answer...

then their efficiency is greatly decreased.

To that end, you can figure out the answer to your question very quickly. The

only thing you need to remember is a special number 206,265 (it is the number of

acrseconds in a radian). The plate scale (which is what you want to compute) is

equal to 206,265 divided by the focal length of your system. That's it...the

whole formula.

So from the values below the plate scale of this 20inch telescope (in mm) is

206265"/3454mm = 59.72 arcseconds per mm.

But you probably want the answer in arcseconds per PIXEL... so you need to know

the physical size of an EOS 350D pixel. The answer is 6.4microns (0.0064mm). So

just multiply your answer above by this value and you have how many arcseconds a

single pixel is: 59.72"/mm*.0064mm=0.38" .

So there are 0.38 arcseonds per pixel. Now you know the field of view. Just

multiply the number of pixels this camera has (3456x2304) and you will get the

field of view. I did this, and converted to arcminutes you will have a 22'x15'

field of view.

By Adam Block, from the ))CCDNewAstro(( Yahoo! group.