And ... yet ANOTHER lunar test!

[bratislav (Bratislav)]

(nothing intentional, Aristarchus just happened to be there last night)

[Peter Ward]

Originally Posted by bratislav

(nothing intentional, Aristarchus just happened to be there last night)

OK, excellent resolution as well What scope?

[bratislav (Bratislav)]

C11. 0.95 Strehl if we are to believe Roddier.

[bratislav (Bratislav)]

Perhaps Roddier isn't telling porkies ...

[Peter Ward]

I've long been of the opinion that c-11's and even more so, C-14's are excellent planetary/lunar imaging scopes. Long FL, closed tube, no spider vanes with good aperture.

I ran a C-11 for many years.... It was an excellent scope

[bratislav (Bratislav)]

Welllll ... they are good buut ...

They are pain to align (you need to do it all the time, and constant removal/attachment of a dew cap is a royal pita).
It is hard to cool the primary inside short of radical surgery (Peltiers).
You need an aftermarkert focuser as mirror flop during focusing is even larger pita at those "planetary" focal lengths.
Corrector dews up so you need to heat it. While cooling the primary at the same time.
It's a miracle SCTs work as well as they do for planetary.

On top of all that, the large obstruction hurts images quite a bit; surprisingly (or NOT surprisingly), just as much as for visual.

This C11 will be relegated from planetary imaging duties as soon as platform for my 16" Dob is finished.

They are fantastically convenient scopes though.

PS give me spider vanes instead of humongous obstruction any time!

[Peter Ward]

Originally Posted by bratislav

Welllll ... they are good buut ...

Yep...with my first CCD (ST4) mirror flop in the C-11 became a major pain.

C-14's are a little more forgiving in secondary mirror size.

As for results...look no further than Damian Peach's superb C-14 imagery.

[bratislav (Bratislav)]

I'm sure Damian would do even better with a large, well figured, small secondary Newtoninan. Yes, it is evidently possible to do great images of planets with SCTs; it is a lot of work though to get around diffraction artifacts caused by a large secondary. It's much easier when you start with good ingredients!
Portability is where SCTs come into their own. C14 can ride on a small mount (even EQ6 would suffice in a pinch). 16" Newtonian either needs a specialized platform (two axis guiding is compulsory) or a monster GEM.
Needles to say, if you fly to Barbados it is the scope that you can bring that gets you best images