Folded Refractor Light Loss ???

Hi
what kind of image degradation can I expect from
a 2 mirror folded refractor design?

Assuming 1/20 wave mirrors?

I was thinking about a 6" F/15 folded refractor
project. But I'm wondering if it just wouldn't be
better to go for a 6" F/12 with a regular straight tube.

Thanks for any information/insights.

Kwang

A folded refractor can work very, very well. John Gregory had an 8" APO folded to work with a Springfield mount at TSP one year, and the views of Saturn were quite astonishing. Quality flats, however, are not inexpensive. Neither are they beyond the abilities of a careful amateur optician.

Well, a folded 6" f/15 is potentially a travel scope, and would be stable on a much smaller/cheaper mount, compared to a straight-tube f/12. If I can get my hands on an objective I would do it :-) I would use a reasonably priced high quality 3" first mirror instead of 4". On the other hand, a 6" f/8 with Chromacor is much easier to own. Good luck with your project,

-- William Chang (Saratoga CA)

Well if you design the scope right, the light loss will only be maybe 10% more than you loose on a normal refractor since the latter is usually used with a star diagonal. I wouldn't fold the scope so that the light returned to the back of the scope; makes it more difficult to mount and baffel. I would set it up so that the light was reflected back up through the top of the tube then you could mount it on a Dob mount . With a little thought, you can probably get the 6" f/15 down to no more than the length of a 6" f/6


--
Bill

if you buy a 6"F/15 achro, add the cost for a nicely made foldet tuibe and addiding the cost of 2 real 1/20 wave mirrors ( ouch very expensiv e) you will end close to the price of a commercial available 6" apo

Markus