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Collimating Refractors
I'm in the process of re-building a Spectroheliograph and a PST mod.
In the SHG I have, what I think is a good lens, a Carton 100/1300 objective.
I normal collimate the OTA - focuser to objective, using a objective target and a laser pointer, followed by the Cheshire side illuminated to show the "doughnut" reflections a la Suiter (p121-123)
I now have a very good variable brightness collimator available, and carried out the usual focuser to objective test.....BUT I noticed a reflected "dot" in the collimator target...this seems to be reflected from the optical surface(s) of the objective.
This reflection can then be used to collimate the objective lens to the OTA and focuser.
This is something new to me, having never used a collimator for this test. I haven't seen it mentioned as a way of collimating the objective, so I thought it would be of interest.
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