How much telescope is too much? If the new baby is going to be installed in a permanent backyard observatory, the sky is literally the limit, and bigger usually is better. This is not so if the CAT must be set up and torn down for each observing run. A too-large first telescope can often bring a swift and bitter end to a budding amateur astronomy career.
The above being said, larger mirrors do enhance visual enjoyment; there is no denying that. Although an 8-inch or 5-inch telescope can do a good job from a dark site, it may be badly handicapped when used from a typically light-polluted suburban location. When light pollution is a factor, contrary to what you may have heard from some amateurs, more aperture is always better. As said in my book, The Urban Astronomer's Guide, skeptics should set up 5- and 12-inch SCTs side by side under light-polluted skies and point them at the great globular star cluster in Hercules, M13. In heavy light pollution, the star cluster is okay in the C5, a little on the smudge side with not too many—if any—cluster stars visible. In the 12-inch, M13 shows its true nature as a gigantic globe of distant suns.
Yes, aperture always wins, all things being equal. Fortunately or unfortunately, all things are not usually equal. Aside from the question of how to pay for a really big SCT, there is always the problem of how to move it. Unless the telescope is going into a permanent home, think long and hard before going bigger than 11-inches.
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