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Focuser Mounting/Tubing

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Posted by Richard on January 16, 2003 00:53:33 UTC

Thanks for the reply Bob. I should have explained a little more as to where I am at with this project.

I found a good supply for 7" ID, 7 1/2 OD tubing. It's free for the taking.I had a 1 1/4 R&P focuser, a mirror cell and a 1.2 diagonal lying on a shelf for years. All that's left to do is make the mirror and put it all together. I was thinking a 8 inch primary might be pushing a 7 inch tube a little so I plugged it all into NEWT 2.5 and hears what it came up with. (The 3.75 Focuser Height is with a inch spacer under it.) That's what generated my initial question. Think I should downsize the primary or go with a larger tube?

Unit of measure inches
Primary Mirror Diameter 6.0
Focal Length 48.0
Focal Ratio 8.0
Tube Inside Diameter 7.0
Tube Thickness 0.250
Focuser Height 3.75
Focuser Inside Diameter 1.25
Focuser Extra Travel 0.75
Focuser Camera Travel 0.0
Diagonal Minor Axis 1.2
Diagonal Offset 0.0375
100% Illumination Diameter 0.2037
75% Illumination Diameter 0.7712
Front Aperture Diameter 6.7309
Mirror Face to Focuser Hole 39.75
Focuser to Front End of Tube 6.0
Mirror Face to Back of tube 4.0
Tube Length 49.75

By the way, if anyone is interested in the 7 inch tubes, check with your local RV repair shop. Replacement awnings are shipped in them.

Thanks , Yarb

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