Next: About this document Up: No Title Previous: Changing from Reflection to
Next: About
this document Up: No
Title Previous: Changing
from Reflection to
Assuming the the camera focus is fine in reflection mode (see section
??) then the transmission focus entails a possible shift in slit focus
relative to that. Firstly set the grism to the correct angle - it is required
to be at 5.2 
to the collimator axis. I believe the grating encoding reads negative for
all used angles, both in reflection and transmission, so the grating angle
should be set to -5200 millidegrees. To check, the grating cell should
be rotated clockwise viewed from above.
Illuminate the fibres with a line comparison source, and take exposures with firstly the right hartmann shutter closed, then with the left closed. measure the Hartmann shift in the centre of the chip, and adjust the slit focus to get the difference (right - left) to be 0.5. Note that a change of +1000 in slit focus implies a change of -0.4 in hartmann shift.