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Hi Brett, there are two compelling reasons to try and get the mirror as a whole to the same temperature as the ambient air:
1. If the mirror is not at the ambient temp then there will be a thermal gradient through the glass that distorts the shape of the mirror away from a perfect parabola, giving the mirror some amount of spherical aberration.
2. If the mirror is warmer than the ambient air then a layer of unstable air forms over the mirror (called a boundary layer) which distorts the image very badly, as light refracts differently through air at different temperatures.
Either one of these effects will destroy the ability of your scope to give high power views of the planets, and both effects together (the usual case) contributes to the poor reputation that newts have for planetary views.
With some effort it's possible to correct both these problems, and then you can get really spectacular views and/or images of the planets.
regards, Bird
Last edited by bird; 04-02-2006 at 03:30 AM.
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