Some Schmidt-cassegrains faster than F/10 were made in the past. Meade made F/6.3 SCT for example. They were not successfull because of the huge obstruction.
We can see a lot of maksutov-cassegrains on the market with differents focal ratios to F/15.
Obstruction is rather small (28 %) and they are contrasty and give excellents planetary images, but they are heavy because of the meniscus.
Do you know why planetary SCTs with low focal ratios were never built ?
-Maybe the large obstruction hidden some higher order aberrations ?
- the system that move and hold the primary Mirror need a large area to control this moving mirror ?
- No need for a 8" f/15 when you can got a 9.25" f/10 ?
- other ?
What do you think about ?
Edited by jjack's, 05 December 2018 - 06:49 PM.