Saturday, December 20, 2003

My Reflector Isn't As Overweight As I Thought

I mentioned a few days ago that my 8" f/7 reflector needed to go on a diet, so that I could get it light enough to fit on a Losmandy GM-8 equatorial mount--and get fully into the 21st century.

I went out and bought a bathroom scale today--and I discovered that it wasn't as overweight as I had thought. The entire OTA (optical tube assembly), including the rotating ring assembly, is only 31 pounds. Going to a carbon fiber composite tube might well get me down to 20-22 pounds--light enough for the GM-8! This is encouraging.

I'm still trying to figure out whether to tackle a more dramatic change. Right now, I have an ancient 1.25" focuser, and a 1.83" elliptical diagonal. It is tempting to switch to a 2" focuser, so that I can use wide field eyepieces. If I go to a low profile focuser, I can reduce the diagonal to 1.3", reducing lost light and diffraction damage to the image.

The downside is that just about all the low profile focusers have very limited range. My current rack and pinion focuser has 3.75" of travel--enough that I can very comfortably use a camera as well, and still have the focal point inside the camera. Low profile focusers generally make you trade off focuser travel for overpenetration into the tube, possibly adding a new set of diffraction problems.

Anyway, there's no urgent need to make a decision right now. I just have to figure out what to do before replacing the current tube. If I am going to drill a bunch of new holes, I would rather do it in the current fiberglass tube, which bears the scars of an unfortunate incident involving my daughter, our Mitsubishi, and the garage.

Oh yeah, feel free to throw money in the tip jar for that Losmandy GM- 8.

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