I'm kind of stuck on building my scope because I can't seem to saw a straight line. But that isn't the point of my post.
I noticed an article from S&T in the archives from October 2001 called 'Downsizing Newtonian Secondary Mirrors' by Ernie Pfannenschmidt. In the article he describes how to build a relay lens which is mounted roughly at the tube wall. The light bounces from the primary mirror to the secondary mirror. About half way to the tube wall it narrows to a point then expands again. When it hits the relay lens (a pair of achromats face to face) the light reconverges over a few inches to the eyepiece.
If you play with your favorite newtonian design in NEWT and make your focuser height a negative number 1/4 that of your tube diameter, you can see how small your diagonal can be. On short F instruments an 8% obstruction is easy though a little bit more gives a better illuminated field.
Has anybody tried this yet? I think I can put a .5 inch diagonal on my 8 inch f9, maybe using a pair of 6x30 binocular lenses for the relay. That is a 6% obstruction!
Mark
I noticed an article from S&T in the archives from October 2001 called 'Downsizing Newtonian Secondary Mirrors' by Ernie Pfannenschmidt. In the article he describes how to build a relay lens which is mounted roughly at the tube wall. The light bounces from the primary mirror to the secondary mirror. About half way to the tube wall it narrows to a point then expands again. When it hits the relay lens (a pair of achromats face to face) the light reconverges over a few inches to the eyepiece.
If you play with your favorite newtonian design in NEWT and make your focuser height a negative number 1/4 that of your tube diameter, you can see how small your diagonal can be. On short F instruments an 8% obstruction is easy though a little bit more gives a better illuminated field.
Has anybody tried this yet? I think I can put a .5 inch diagonal on my 8 inch f9, maybe using a pair of 6x30 binocular lenses for the relay. That is a 6% obstruction!
Mark
