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The corrected Dall Kirkhams seem all the rage now with several on the market.
There's Planewave Instruments who make a 12 inch (F9), 17 inch (F6.8) and 20 inch at low prices (relatively that is).
There's Orion Optics UK who make corrected Dall Kirkhams up to 16 inch I think but not in the hands of users yet but probably a nice scope (F6.8).
Then there's the Ceravolo Astrograph which 300mm and both F4.9 or F9 but you need a corrector for each F ratio and they are expensive.
A and M Astrotech also make a beautiful tubed one as well as a gorgeous Mak Cass with Carbon Fibre tube. They are somewhat expensive.
Mewlons are really more visual instruments and I don't think they have a real large corrected circle for imaging but there are some OK images around from them.
There are also some RC scopes coming out that are cheap like the DSI 10 inch and the Astrotech 6, 8 and 10 inch.
There is also an RCOS 10 inch Astrograph at F7.0.
As Fred says it boils down to megadata as in long hours of exposure and I would add fast F ratio (though that tends to make you more widefield unless you use a small chipped camera with high QE).
Greg.
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