Re: ATM Spider Design

[andydtg@alpha1.phoenix.net]

Michael wrote:

>I have heard that the three vane design causes six
>diffraction spikes, not three, while the four
>vane design causes only four diffraction spikes.

True. Just remember that secondary support diffraction
is caused by the edge of the obstruction & has nothing
to do with the thickness of the support. The diffraction
spike is actually formed at 90 deg to the edge causing it.
This is why a support with 2 vanes at 90 deg will still
produce 4 spikes, with intensity of 1/2 the amount from
a full 4 vane support. Circular vanes eliminate or reduce
spikes because the diffracted light is not preferentially
aligned as with straigt edges.

Andy Saulietis / DTG Alt-Az-Fp Drive Systems
12617 Harriet Ln
Santa Fe, TX 77510 USA
409-925-8854 Voice/Fax