field of view calculator

[slimfb]

noob questions i'm afraid

* can the FOV calculator be used as part of the decision making process for choosing a scope ?

to retain a 'like for like' resulting image do i have to change the EP's according to the scope ?

i just want to compare what i will eventualy see with different scopes

is a bigger image better ?

thanks to the poster for the original link........interesting

http://www.12dstring.me.uk/fov.htm

[acey]

Unless you're specifically looking to maximise field of view (and have some specific reason for wanting to do this) it shouldn't really be a consideration.

The FOV of a telescope is determined by two things: the focal length of the telescope and the field stop of the eyepiece (the width of the glass at the bottom end of the eyepiece, which is limited by the width of the focusser barrel).

Let's say it's a 1.25" focuser, then the maximum possible field stop is about 27mm. Suppose the scope has focal length 1000mm, then the maximum field of view is 27/1000 = 0.027 radians. Multiply that by 57.3 to convert to degrees and you get 1.5, or about three times the width of the full moon. Choose a shorter focal length and you'll get a bigger field.

This is assuming your eyepiece has the widest possible field stop; as you raise the magnification the field stop gets smaller and you see a smaller field. But short focal length always gives a wider field than long focal length, for a given eyepiece.

Does that mean you should choose a scope with a short focal length? Not necessarily. Magnification is determined by focal length; the greater the focal length, the higher the magnification for a given eyepiece. For planets you'll want to use high power, and a "short focus" instrument wouldn't be good, though it would give nice wide-field, low-power views.

So I would forget about FOV for now and think about other considerations such as weight, portability, convenience etc.