I have a fine 130mm apo, and I am mostly a lunar observer. I now want to go up in aperture. I am considering a 150-160mm app or a Celestron EdgeHD 9.25 SCT. (An EdgeHD 11 might be too big for me to handle comfortably.) I might consider a Takahashi Mewlon (but which one?). Any advice?
So far, I see a lot of solid advice here, based upon experience.
What is your budget? That has a first order affect on your choices, as does the mounting.
Around here in SW Ohio, an 8" aperture is a very usable size for lunar/planetary viewing. Which typically means an SCT or newt. My problem with most SCT's is finding a sample with excellent and smooth optics. So far, I've found only two, my friend's humble C8 and my plain C11. Both give excellent lunar views but I find myself tweaking focus a fair amount because of the large central obstruction and there seems to me to be a certain residual instability to the image, especially with border line seeing conditions, which I lay at the feet of thermals and large obstruction.
I am fortunate to have a permanently mounted TEC 200ED, which suits my needs perfectly.
Having said that, I'm continually impressed with the lunar performance of my TEC7 Mak. The optics are superb...period. The central obstruction is "small" at ~25% of the aperture and the F15 focal ratio gives an excellent image scale...no barlow needed around here. The images have that abrupt, etched like quality I've found in very high quality optics. It is thermally well behaved for a larger Mak too. My Intes 7" F15 mak was excellent as well.
So, I can certainly recommend from my own experience something like that as it is a significant step up in resolving power over a 5" APO but also light in weight. Even a TEC8 mak might suit you too. Both can be found on the used market but you will have hunt them down. A used TEC 7 will be in the $3500 range and the TEC 8 in the .....well, considerably more. The intes M715 fetches $1200 to $1500, which is certainly cheaper but they are a bit heavier with a lower build quality (though I find the focusing mechanics clever and well done).
Then there is something out of left field like an Intes MN76 mak-newt. Simply wonderful scopes for lunar/planetary work. But bigger, but with a 20% central obstruction, but no diffraction spikes from a spider.
I've provided some pictures.
Now, let's talk about bino-viewers.....