Up: Analytical expressions for field
Explicit expressions in terms of fundamental telescope parameters
of a two mirror telescope can
be derived for the
coefficients describing the field dependence of
third order astigmatism. Of particular importance is the dependence of
the coefficients on the position of the stop. In addition,
these parameters are recalculated for a reference system where the
center of the adapter is at the origin. The numerical values are used
to show that from the measurement of the field dependence of third
order astigmatism at eight locations in the pupil the axes of the
primary and secondary mirrors of the VLT can be aligned with an
accuracy of approximately 7''.
Acknowledgements
The authors would like to thank Ray Wilson for helpful comments and
discussions.
Up: Analytical expressions for field
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