Came across this on CN today, so I thought I would share it here.
The Gregorian telescope uses a doubled mirror primary and a flat secondary making it possible for the OTA length to be 1/7th of its focal length. Imagine a 2100mm focal length scope the size of a 12 inch ruler.
I note the article was written in 2004 so I have no idea if these ever went into full production.
https://www.photonics.com/Articles/C...ary_and/a19919
Cheers
Bill