A "rich field" refractor is a refrector that has a focal ratio of f/5 and
lower. Focal ratio is the Focal Length divided by the the aperture. For
example, a scope with a 1000mm focal length (FL) and a 254mm (10") aperture,
has a focal ratio of 4 (3.93 really), written as f/4.

Charles
Nashville, TN USA


"Alan Buttivant" wrote in message
...
I am new to astronomy and have been looking at a number of telescopes. Can
someone please advise : What is the definition of "Rich Field Refractor"
ie
what does it mean. I havn't been able to find out on the web.

Sorry if this is a dumb question.


Regards

AB