ATM Forum Message Forums: Atm · Astrophotography · Blackholes · Blackholes2 · CCD · Celestron · Domes · Education Eyepieces · Meade · Misc. · God and Science · SETI · Software · UFO · XEphem
 Be the first pioneers to continue the Astronomy Discussions at our new Astronomy meeting place...The Space and Astronomy Agora Re: Diagonal Mirror Size??? Forum List | Follow Ups | Post Message | Back to Thread Topics | In Response ToPosted by Anthony/">Anthony on April 24, 1998 14:23:22 UTC

: How big of a secondary mirror do I need for an : 8" f/6 Newtonian?

Hi there. To answer your question you need to decide on a few determining factors. How far away from your primary mirror's focal point do you wish your diagonal to be placed. l*----------------f1-------------*l l l l ----* "P" *----- l l l l---------------------------* l l * * l l *D D2 * "+" l * * Focal ----------------------------* Point

Dimension "P" determines the size due to its set- back from the focal point. Here is a formula I picked out of Texereau's book. D1" x P" D2"= -------- f1" D1 = diameter of your Primary mirror, 8"inches p = the setback shown in the sketch "?" f1 = your focal length, eg 48"inches.

8" x 10" eg 1.66" --------- minor axis 48"

Check to see what's available at your local supply house, and let me know how you make out. Good luck