Quote:
Originally Posted by Brian W
In particular (1) how much would the added mirror cut down on what is seen (2) how is it collimated.
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1) Depending how it's done, the folding flat should not have any ill effects.
If anything, by folding the beam to the side well in front of the primary mirror, it is possible to have a shorter back-focal length than is usually the case with a Cassegrain. This can be used to advantage, either:
a) to achieve a lower focal ratio for a given secondary obstruction, below f/10; or
b) to achieve a smaller secondary obstruction for a reasonably high f/ratio (f/10 - f/15)
2. Adjust the height of the flat in front of the primary so the beam comes out perpendicular to the optical axis (various ways to do this). Then adjust the tilt and rotation of the folding flat first so that the secondary mirror appears centred in the flat; a Cheshire eyepiece will help, or alternatively you can put a spot on the centre of the secondary and use a laser collimator in much the same way as you would collimate a Newtonian secondary.
Then collimate as usual for a Cassegrain,
