Measurements of typical shifts in the position
of a star on the CCD (y direction, in arcsec), when inserting a filter
from wheels 1 or 2 in the light path, are given below:
| Filter | BESR #233 | SloGunG2
#219 | SloGunR #216 | SloGunI #217 | GG395A
#705 | GG495A #706 | T4686 #189 | T6652
#150 | T6757 #162 | T4550 #97 | He4685
#80 |
| Shift (arcsec) | 0.12 |
-0.01 | 1.54* | 0.05 | -0.32 |
0.02 | -0.37 | 1.44 | -0.15 |
-0.20 | 0.06 |
* The SloGunR filter introduces a large shift, and
also a ghost, with a 10 arcsec shift (i.e. displaced 8 arcsec from the main
image).
The tabulated shifts correlate with
the laboratory-measured tip-tilt terms in the
wavefront distortion
introduced by the individual filters,
roughly as: abs(shift (arcsec)) ~ 0.1 ( abs(tip) + abs(tilt) ) / 2, and where
tip and tilt are in waves.
