Quote:
Originally Posted by Visionary
Many thanks Brian & Pluto. It's difficult getting my head around the fact that a 6" (refractor) opening to the heavens can produce as useable an image as a 12" (reflector) it seems counter intuitive. The amount of light falling into a 12" opening is far greater than a 6" opening it seems as if the refractor Is working some l"magic".
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The reason you can't get your head around it is because it isn't true.
A 12" reflector has four times the light gathering power of the 6" refractor, and will see far more galaxies and other faint DSOs than will the refractor.
A 12" reflector has far more resolution than a 6" refractor, and will be able to split tiny little double stars that are invisible in a 6" refractor.
But reflectors have a central obstruction which affects resolution and contrast, compared to the same sized refractors. This means one needs bigger reflectors to get the same good view of a planet. But by getting bigger reflectors, one gets other problems like air currents in the tube and more susceptibility to poorer images from the atmosphere.
Dickenson and Dywer in the "Backyard Astronomers Guide" suggest a good 5" APO refractor is comparable to a good 8" Schmidt Cassegrain for doing stuff like looking at planets. But the 8" Schmidt Cassgrain will kill the refractor for stuff like looking at galaxies.
Refractors images are satisfying because one gets really nice views of stars/open clusters with lots of points instead of the lots of blobs that one may often see in reflectors, particularly early in the night. And the more contrasty view of planets compensates for the lesser resolution, relative to a reflector.
That said, the best planetary views I've ever seen bar none were through a club member's 10" reflector which he put together with the best parts, and which he had optimised for planetary viewing
Regards,
Renato