Ian, the words prime and focus, were stolen and twisted by the astronomy community from the original latin derivations which were nothing to do with Astronomy or telescopes so how they can lay claim to exclusive use eludes me. Another example, the term hole in "black hole" is totally incorrect, the object, if it exists, is not a hole, nor does it have any of the properties of a hole, so astronomers, even professional ones are also guilty of twisting the meanings of words to suit their ends. Now let's examine your Sig I note you have in your sig a 12" F5 Dob, rather odd because as everyone knows the term dob relates to the mount and not the optical assembly; one presumes you have a Newtonian on a Dobsonian base. Really....I would have expected better from one so pedantic.
