TRADEOFF BETWEEN SIZE & B

Mike Abercrombie (abercrom@southwind.net)
Wed, 26 Apr 1995 23:11:34 -0500

DD> A 10 inch f/4 scope is much shorter than a 10 inch f/10 scope, DD> however. My question specifically deals with this tradeoff between DD> the desire to minimize physical size on the one hand, and DD> background atmospheric brightness on the other. What have people DD> found to be a good compro- mise? What f/number works best? Steven,

Why not have both? I like the high contrast that a well figured long focal length provides if combined with a small secondary mirror. I'm now constructing an 8" with a focal length of 75.625" (almost f/9.5). this scope will utilize a 1" secondary (purely visual!) in a tube that is both 7' long and at the same time only 3.5' long. In other words, the tube is in two sections for transport.

I'm making the tube completely out of 2mm plywood...even the bulkheads. The corners on the bulkheads will be reinforced with 3/4" triangles to allow a surface to attach the sides of the tube (screws don't go into the edge of 2mm plywood very well). I'll be using some 1" triangular stock as molding for the seams on the inside of the tube for added strength.

A collar on the mirror half of the tube will act much the same as a joint for sewer pipe for connecting the two halves. They will be secured into place with four chest-latches, one on each side.

I'm sure that I'll have to recollimate each time I set the thing up, but hopefully, I won't be that far off and this I think is a livable compromise for having a long focal length scope that is easily transportable.

Mike

* RM 1.3 * The tuna doesn't taste the same without the dolphin.