The distance from lens end/T2-male-thread to getting focus at the end of a 20cm Plossl is roughly 8cm. With my lens.
And if it needed a longer light path there are focal correctors - by the way usually sold - or at least offered - with binoviewers, anyway. A bit like barlows.
If needed - I would probably be okay with 1.7.
That puts my "Mak" still in a very favourable fastness over "normal" Mak scopes.
No reply from Celestron-Germany yet.
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