&thetacc = camera-collimator angle (deg)
dcg = collimator-grating distance (mm), taken to be surface 32
dc33 = collimator-surface-33 distance (mm): surface-33 is near the pupil but not at it.
dcp = collimator-pupil distance (mm)
dcc = collimator-camera objective distance (mm)
dgc = grating-camera distance (mm)
dpc = pupil-camera distance (mm)