Re: ATM (no subject)

[andydtg@phoenix.net]

>Well, I for one, fell that it's about time we start demanding that
>telescope manufactuers produce egg-shaped diagonals.  When you think
>about it, that's the shape you get when you cut a cone at a 45 degree
>angle.  It would provide a smaller obstruction and would appear, to the
>eye, to be closer to round when viewed through the eyepiece tube.
>
>Regards,
>  Fred Maxwell
>
>P.S.  The above is only half-serious -- though technically correct.

*Any* plane section of a cone that intersects in a closed line is
by definition an ellipse. It's geometric center does not lie
on the axis of the cone except in the case of a section perpendicular
to the axis = a circle. The difference between the cone axis &
the ellipse center is the 'offset' that seems to be causing so
much collimation difficulty.

The alignment situation is much clarified if one diagrams the
imaging cone with the apex where it is for the edge rays (thru
edge of fov at focus), behind the focus. The system, with offset, 
will appear circularly symmetrical if viewed from this apex.



Andy Saulietis / DTG Alt-Az-Fp Drive Systems
HDPE Worm Gears, Custom designs & Machine work
12617 Harriet Ln
Santa Fe, TX 77510 USA
409-925-8854 Voice/Fax
e-mail: andydtg@phoenix.net