Alan Buttivant wrote:

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.

It is a refractor which has been developed to provide wider fields of view at
lower power than other long focal length "planetary" refractors. Usually,
there is not a strict f/ratio definition, but you will often find simple
2-element objective refractors with f/ratios of f/6 and lower termed
"rich-field" instruments. Their performance at very high power isn't quite as
good as with some of the much longer f/ratio refractors, although they can
often still provide at least passable high power performance. I have a 100mm
f/6 refractor and it provides some of the best wide-field views of the night
sky I have ever seen, although its high power performance would definitely put
in the "rich-field" class. The Apochromatic refractors (3-element or more
objectives) like the TeleVue 101 are more "all-purpose" instruments than
rich-field despite their shorter f/ratio. This is mainly due to the high
quality of their objectives which allows good to excellent performance at just
about any power, and over wide fields of view as well. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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