This has been discussed many times before.
1. There are only two SCT manufacturers currently in the market - Meade and Celestron (Synta). Take your pick, they are like Fords vs Chevs. Both are mass-manufactured, low price is clearly the priority over optical quality.
Celestron has a few variants - the bog standard SCT, Edge HD, and the Hyperstar or RASA for imaging types.
Meade ACF are the alternative. But note they do not guarantee the optical quality, no mention of "diffraction limited" let alone a guarantee that the scope passes ¼ wave (never mind 1/8 waver PV) so you take your chances. If you receive a dud, so be it.
2. Cassegrains - classical, Dall Kirkham and RC from GSO and others.
3. Takahashi Mewlons - I've only seen three 250mm ones - optical quality seems to range from good to very good, but they have a secondary supported by a 4-vane spider, so expect diffraction artifacts.
4. Vixen sub-aperture maksutov cassgrains - IMHO deserve 4 out of 10 - poor optical quality, fat 4-vane spider...
5. New mass-manufactured maksutovs at budget prices - Skywatcher/Celestron (ie Synta), Orion UK, Explore Scientific, Bosma, Saxon. The Skywatcher ones are consistently very good optically, 9 out of 10.
Orion UK have a very poor reputation.
6. There are a few sources of premium quality large maksutovs larger than 180mm - Astrophysics, and Ottiche Zen in Venice. APM (Germany) may have one or two left. Real artisan craftsmanship, optically excellent but this comes at a price.
7. Then there is Questar, a special case in terms of quality and price. They are works of art.
8. Secondhand - Good quality Maksutovs from Intes appear up reasonably often here at CN Classifieds, or on "that other website", and at Teleskop-Express in Germany,
9. The "unicorns" - rare, legendary premium maksutovs with exquisite optics known to exist, a few have actually seen one, and a very lucky few actually own one. These are rare, and you have to some work to find one let alone acquire one in good condition.
Examples include the big maksutovs from TEC, Santel, Astrophysics, Ceravolo, APM/Matthias Wirth, Intes and the Questar 7" and 12". These are the Ferraris and treasured accordingly. The point is that Intes, Santel and APM guaranteed optical quality. For Questar, AP and TEC .. don't bother to ask, it is THAT good. But this kind of quality comes at a cost.
Edited by luxo II, 10 October 2019 - 07:02 AM.