09/06/2001
Information about the prime focus of the Viper/SPARO setup.
The Viper/SPARO template has a hole drilled in it where the drawn-on rays converge before impacting the secondary. This would seem to be 'prime focus'. This point makes a convienent origin for various template coordinate systems with which to analyze the template itself. Since the rotation aspect of the transformation is farily straight forward, it would be nice to nail down the translation aspect, as well.
At the beginning of the analysis of the tertiary (detailed here), the following Beam4 ray trace file was used:
The optics file used was this:6 rays sparo.ray Y0 X0 Z0 @wave ------:--------:----:-------: 0.000:1.300000:-1.0: B 0.000:1.000000:-1.0: : 0.000:1.600000:-1.0: : -0.350:1.300000:-1.0: : -0.350:1.300000:-1.0: :
sparo.opt
Z X Y C S Mir/Len T P R
--------:---------:-----:--------:---------:-------:-----:---------:-----:----:
1.5 : 0.0 : 0.0 :-.333333:.01020408: mirror: 0.0 : 0.0 : 0.0 : :
-0.5 : 0.0 : 0.0 : 1.1429 :.41699219: mirror: 0.0 : 0.0 : 0.0 : :
-.00273 :-0.07317 : 0.0 : 0.0 : 0.0 : mirror: 0.0 : 0.0 : 0.0 : :
-.589941:-1.148669: 0.0 :1.023577:-1.30073 : mirror: 0.0 :92.935396: 0.0 : :
-.60982 :-0.76102 : 0.0 : 0.0 : 0.0 : detect: 0.0 :-36.51063: 0.0 : :
: : : : : : : : : :
: : : : : : : : : ;
The crucial matter is this: the primary is an aplanatic mirror, and thus, has no well definied prime focus point like a parabolic mirror would. Therefore, instead of a single point, there is a focus 'smear', of which the centroid is at approximately (0.004, 0.002) in Beam4 coordinates. After repeated investigations, however, trying to work out the translation was an unneeded piece of information. The measurements made on the template are offset a consistent amount, demonstrating that to within a few millimeters, the template is correct.
Still note however, that definining the prime focus hole on the template as the origin still introduces some error, but for our purposes, it is close enough.