1.25 Para-Corr

I want to make a travel scope, and one of the design elements is a very short focal ratio (an 8" F3.8 is what I am shooting for). I plan to stick with long Plossls (40 or 32), a Tele-vue 8-24 zoom, and a barlow. All 1.25....

How much do I have to worry about Coma?

More specifically--Is there a 1.25 inch version of a coma correcting optic? They seem to be all 2 inch barrels--not in keeping with my minimalist design.

Alex

>>>>I want to make a travel scope, and one of the design elements is a very short focal ratio (an 8" F3.8 is what I am shooting for). I plan to stick with long Plossls (40 or 32), a Tele-vue 8-24 zoom, and a barlow. All 1.25....

How much do I have to worry about Coma?

More specifically--Is there a 1.25 inch version of a coma correcting optic? They seem to be all 2 inch barrels--not in keeping with my minimalist design.

Alex
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Alex:

A few thoughts and comments... I have a fair amount of experience with fast scopes, my main scope for several years was 12.5 inch F/4.06, my main one now is F/4.42. Lots of F/5's.

- There was a 1.25 inch Paracorr but it is quite rare and I think those who own one are probably keeping it. I have one, it's something I rarely use as I also have a 2 inch but I am holding on to it.

- With the eyepieces you have chosen, I doubt the coma will bother you much simply because the eyepiece astigmatism at F/3.8 will be rather severe. Note too that a 32mm Plossl will give you an 8mm exit pupil.

In my experience, one can get stunning "refractor-like" views from an F/4 scope, but it takes the good eyepieces as well as a Paracorr. With Plossls and the Zoom, not so good. I think most people who are satisfied with an F/4 Newtonian have Naglers and the like, it sort of goes with the territory.

Personally I like F/5 much better. I know F/4 will save you some length but an optimized for length 8 inch F/5 can be quite short, I believe my early model Konus (reputedly the "good one") is about 36 inches long. One can get by without a Paracorr and still get reasonably well corrected views.

- Given our mutual connection here and through your brother, I would be willing to loan you my 1.25 inch Paracorr if you wanted to try one out to see if it makes a difference.

Best to all...

Jon