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I've never owned a TV scope. But a doublet is not an APO its a semi-APO. All doublets are semiAPOs. Theoretically a doublet could be made APO but I am not aware of any that were.
Mind you it is probably a superb semi-APO. But to be fair APO has a definition. It mean s 3 main wavelength colours are in focus at the same time. Not sure which colours but something like RGB (its not RGB but similar). Doublets typically get 2 the same and one fairly close (usually blue/violet). Super APO means 4 colours in focus at the same time. These terms get degraded for marketing purposes.
Visually as eyesight is heavily biased towards green (TEC gets the green at over 99% strehl for this reason) it may seem fine. But image with it, especially a one shot colour like a DSLR and you will most likely have blue haloed bright stars.
One bright objects like the moon or Jupiter you may see a tad of colour a the fringes but not especially objectionable. Otherwise it is hard to notice.
MY Tak FS152 was a fluorite doublet and despite being semi APO it still gave some of the best views I have seen in any scope.
It tends to give a slightly warmer look to some objects because the blue is slightly out of focus.
True APOs may make objects look cooler.
Doublets though are light, cool down very quickly (my FS152 cooled down super fast). The Tak fluorite doublets gave snap to focus images that are very sharp and highly contrasted. The extra contrast helps give more detail in viewing.
The TSA102 from what I have read as was mentioned is about as good as it gets with triplets. I read a post from a guy who has owned about every high end APO imaginable (various AP scopes, TEC, TMB) and he thought the TSA102 was one of the very best in its class.
Tak usually gets all the other parts really right as well.
My main complaint about Tak is twofold:
1. When you buy one you need to buy the rings, the finder scope, the quick release brackets and lots of adapter for imaging. You stretched yourself for the scope and the addons add another $1200 (no case either).
2. Their threads on their adapters are notorious for binding so badly you may not be able to remove them. I nearly destroyed a reducer because it got locked on so badly. I always coat the threads of new Tak threads with teflon grease (thin wipe) to stop this from happening. They seem to paint a high friction paint on their already very narrow threads.
Greg.
Greg.
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