Re: Wire Spiders for Planetary Reflecting Telescopes

[OPTIXWIZ@aol.com]

In a message dated 95-10-07 17:28:15 EDT, you write:

<< s >>

Rik, there's more going on with an obstruction, such as by a spider, than
merely the diffraction from each edge of a thin rectangle of obstruction
stretching to the center of the aperture.

The spider obstruction is subtracting out energy from the point spread
function, besides the redistribution of existing energy by diffraction.

Then there is the issue of refraction caused by a thin mantle of (cold?) air
adhering to conventional spider vanes, because the vanes are a different
temperature (colder?) than the surrounding air. This causes conventional
spider vanes to appear thicker than they are insofar as the drop in MTF and
degradation of the point spread function is concerned.

Well made wire spiders work spectacularly well!!!!!!!!  Used in conjunction
with good, well collimated optics, a well ventilated telescope, in reasonably
good seeing, and the planetary performance is absolutely fantastic!

Gene Cross
La Mirada, CA