Quote:
Originally Posted by multiweb
Any corner in the light path will create diffraction patterns and light scattering. I would not recommend it if your mirror doesn't fit in the shadow of the round holder.
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If the secondary mirror is larger then the refection of the primary, then there would not be a corner.
The reason I am trying to find out is that I would like to make a mirror for a autocollimation test stand, the mirror would be a perfectly flat one with a hole in the centre.
To make the mirrors flat, I need 3 pieces of glass. If I am successful and I will try to be, I would have 3 flats and could use one for the autocollimation rig. That leaves me with 2 flats. To cut the oval at a 45deg angle would be more difficult again. So I could use one for a secondary.
If one would get a secondary twice as large as required, would it matter other than the weight and the cost?