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My version of the Turret Telescope

Started by dsimons, 03/21/2004 01:22AM
Posted 03/21/2004 01:22AM Opening Post
Many years ago I read about a funny kind of telescope design used at the Stellefane Convention. It was called the "Turret Telescope". It used a perforated flat to direct the star light towards a parabolic mirror, and the parabolic mirror was aimed at the flat, such that the focused image went through the hole in the flat. The eyepiece then viewed the image from the other side of the flat. The observer viewed the image from the inside of a large polar aligned turret.

Here is my setup to get the same kind of image. (Sans Turret) I could only slightly tip the telescope towards some low stars since I did not have a mounting yet. Sirius looked great, and lots of little faint stars all around it. The in and out of focus images looked like a refractor with a very small black dot in the center from the perforation. I was using a 10" mirror and flat combination with a 1.2" hole giving 12% obstruction.

I hope to get these optics installed in an aluminum tube with a large oval cutout to bring the light in from the side. Baffling this scope will be a challange.


David Simons

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Posted 03/21/2004 09:48AM #1
That's very interesting but I have one question. Why?

What's the advantage of a scope like this over a standard newtonian design?
Posted 03/21/2004 09:25PM #2
Hi Craig D.

Thanks for the reference. I found some short references to Fundy Scope in the ATM archives, and SAA. Basically the same idea, except the ATM archives mention using the flat at large angles such as 45° which require very good optical figures on the flat. I discovered the effect you refered to about tilting the flat that allows you to shift the image without actually moving the telescope. Kind of a handy side effect.

Since I am using a very small narrow angle for the incoming light instead of a larger angle, I get to cheat a little on the quality of the optical flat. It's actually not perfectly flat, but I think it has a spherical focal length over 100 miles. It's a very smooth spherical surface (almost flat), hence it was much easier -read cheaper- to make. The fellow who made it for me included an interferogram, that had very clean lines. I am sure there will be some astigmatism, but is it enough to ruin the image? I have more testing to do !

The only decent image I have so far is from Sirius and the surrounding stars. It was a little low on the horizon for decent testing. But when it was still for a short while, the sharp image of Sirius was enough to keep me working on this scope.


David Simons