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Originally Posted by janoskiss
I had the same impression regarding coma as you, but I'm not convinced that this is correct. Eyepieces don't fix coma, do they?  |
Steve,
Eyepieces can actually correct for coma.
Generally this occurs specifically with a given eyepiece design, a given eyepiece focal length in a given telescope design of known aperture and focal length. It does not generally happen generically. In other words you can't conclude that because a 7mm T6 Nagler corrects Coma in a 10"/F5 newt, that a 13mm Nagler T6 will correct Coma in a 6"/F4.5 newt. There have been attempts at producing "coma correcting eyepieces". University optics came out with a "Pretoria Design" in the mid 80's that was a coma corrector. How will did it work? Dunno never tried it, but try buying one now
I think you guys meant to use the term astigmatism, as opposed to Coma? Coma generally is not a major issue with an F5 Newtonian and only manifests in scopes faster than F4.5.
CS-John B