: There are some professional multi-mirror telescopes in existence, but is an amatuer version possible? As we all know, mirrors get expensive as they get bigger, more precisely the square inches per dollar gets higher as the mirror gets bigger, presumably because it's harder to make, the manufacturers sell less, etc. But you can pick up some bargain small mirrors, for example Surplus Shack has 3" f/10 mirrors at $8. Imagine 6 of these arranged in a circle, each with its own mirror cell, and each tilted slightly inwards, projecting onto a secondary mirror. Unlike a "normal" secondary mirror, this could be quite big, almost any size would do because it wouldn't obscure part of the primary, because there would be a central gap between the 6 small mirrors. The focusser/eyepiece arrangement is as normal. Six 3" mirrors have the same light gathering area as about a 7.5" single mirror, and so would be approx equivalent. The question is ..... would it focus OK? You could adjust each small mirror separately during collimation (that would be fun?), and after that it would be focussing as normal.

: Obviously you'd want all the mirrors to be as exactly similar as possible. Surplus mirrors could probably achieve this, as they were probably all made for the Govt to exacting specs.

: Has anyone ever tried this? I guess it could be tested fairly easily with say 2 or 3 mirrors, before committing to the full array.

Interesting idea, but think BIG. 4 x 12.5" mirrors = 25"!!!

But seriously, in addition to the focusing challenge you mention in your post, one also would encounter a difficulty with the figure of the mirrors. Technically, Since the mirrors would need to be tilted, a regular parabolic mirror would not be appropriate. For optimal performance, I believe the mirrors would need to have an off-axis paraboloid figure. I haven't crunched the numbers to find out how important this factor would be, but I have a hunch its non trivial (and would certainly depend on the size of the scope in question). In any event, such a project would certainly pose an entertaining optical, as well as mechanical, challenge.