Quote:
Originally Posted by bmitchell82
its very interesting indeed Clive, as it gives people a good idea on what generally happens with scope cool down times. I guess depending on your mirror substrate the 1-2 deg difference of mirror to ambient wouldn't pose much of a issue when looking at pyrex.
What are your thoughts on that?
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The issue isn't so much a question of heat induced distortion of the substrate as it is the convective plume at the boundary layer distorting the image through variation of the refractive index of the air.
There is a qualifier to that... if the mirror substrate hasn't been correctly annealed then you will see the mirror figure do bat**** crazy things as it equilibrates thermally. (even if it is pyrex) Basically you will see astigmatism at the focal plane come and go as the optic cools.