34 replies to this topic

[azure1961p]

My experience is - and not pointed at anyone in the thread - the majority of people don't know how to do scope testing on planets and moon.  I'd take a good C9.25 over any 6" because the Rayleigh advantage, despite the CO will reveal itself in the 9.25 on the smallest most challenging details.  If it's a good C9.25. 

 

Too many folks lope along at pedestrian magnifications and generalized large details (festoons, GRS) but don't seek the finest details under the highest powers each instrument can manage to truly access there diffraction limit potential.

 

At 200x with both scopes, probably the refractor. At 400x on Ganymede, hands down the SCT here.

 

Pete

[GTom]

For the Rayleigh advantage besides perfect collimation and optical quality, you have to assume perfect seeing as well, especially for visual.

Point taken though, when seeing allows, aperture is king!

Edited by GTom, 19 November 2024 - 01:23 PM.

[azure1961p]

You don't need perfect seeing.  Fair will do it.  Though obviously, "perfect seeing" benefits everything. It's just not needed.

 

Pete

[GTom]

You don't need perfect seeing.  Fair will do it.  Though obviously, "perfect seeing" benefits everything. It's just not needed.

 

Pete

For the comparison, you definitely need that the seeing doesn't affect the two systems differently. Yes, that can be a non-perfect scenario, but that case it's difficult to exclude seeing effects from the equation.

[lwbehney]

For the Rayleigh advantage besides perfect collimation and optical quality, you have to assume perfect seeing as well, especially for visual.

Point taken though, when seeing allows, aperture is king!

Bingo!  This is the great advantage of the six inch refractor over the C 9.25. The atmospheric seeing will degrade the larger aperture telescope’s performance much more than it would the smaller refractor.  IMHO, if you live in a locale with mediocre seeing, then a six inch refractor will be giving the better views compared to larger aperture instruments. Read the experiences in these fora of a CN contributor regarding his comparison of his six inch f/6 APM refractor compared to his larger instruments. Six inches of unobstructed aperture is very significant when chromatic aberration is well-controlled. 

[GTom]

Bingo!  This is the great advantage of the six inch refractor over the C 9.25. The atmospheric seeing will degrade the larger aperture telescope’s performance much more than it would the smaller refractor.  IMHO, if you live in a locale with mediocre seeing, then a six inch refractor will be giving the better views compared to larger aperture instruments. Read the experiences in these fora of a CN contributor regarding his comparison of his six inch f/6 APM refractor compared to his larger instruments. Six inches of unobstructed aperture is very significant when chromatic aberration is well-controlled. 

As a matter of fact, I hear very good feedback from larger mak users too and I myself had a 7" classic cassegrain years ago, which turned out to be a great OTA for Mars. The scope landscape is vast

[quilty]

For Mars any scope allowing high powers is a great ota. Everything below 300x is pointless (to my eyes)

[quilty]

Bingo!  This is the great advantage of the six inch refractor over the C 9.25. The atmospheric seeing will degrade the larger aperture telescope’s performance much more than it would the smaller refractor.  IMHO, if you live in a locale with mediocre seeing, then a six inch refractor will be giving the better views compared to larger aperture instruments. Read the experiences in these fora of a CN contributor regarding his comparison of his six inch f/6 APM refractor compared to his larger instruments. Six inches of unobstructed aperture is very significant when chromatic aberration is well-controlled.

What about acclimatisation? I just learned (from Astrojensen) that a 6" frac takes at least 1 hour for high powers.
My 9 1/4 takes none. Insulating just does for cats but not fracs.

weather's dreadful like usually at optimal moon times. Flocked the dewtube of my 9 1/4 today with dc-fix, maybe next year I can tell if it's worth it. Really black now. Or in 2026

Edited by quilty, 22 November 2024 - 10:58 AM.

[lwbehney]

My experience with my five inch doublet refractor is that temperature acclimation is faster than 20 minutes and less than that unless the temperature delta is > 30F. Maybe fluorite doublets have a lower heat capacity?

[quilty]

Or Skymax