While I cannot give you the optical specifications for the 16" LX 200,
I can suggest a way to simplify you task. This should give you a good
idea about the vignetting with attachments.

However the light reaches the baffle tube, it is the baffle tube that
limits the light rays trying to reach the image plane. Thus you can
assume that there is a bundle of roughly parallel rays going down the
tube and coming out of the back of the telescope. This bundle is
about 2" for the 12" scope but a bit larger for the 16" scope. I do
not know the exact size.

This sort of rough ray trace can be done with a ruler on a sheet of
paper since only the edge rays need be traced. An optical program is
not required.

You can then place your various field stops in the light path and see
what happens to the light rays. It becomes very apparent, very
quickly, where the trouble spots are located.

I would suggest that if you want to illuminate larger chips, like the
ST8 or larger, you will need to use 2" filters in the light path. I
have never found full illumination of the larger chip with a focal
reducer stronger than 0.63. But vignetting is a gradual reduction of
the light, so to some extent you can help the situation with good
flats.


Doc G

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