Quote:
Originally Posted by gregbradley
Wow, I did not realise that fans could have that effect. I only mentioned the fans blowing across the mirrors as the latest CDKs have that (4 of them) plus the 3 or 4 at the back.
Greg.
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In its original configuration, my 16" planetary had 7 fans. Three of them on the back plate in sucking mode, an the other four were removing the boundary layer. I tried the cross blowing ones in various combinations of sucking and blowing but in the end I had to give up and remove them.
The astigmatism problem could only be revealed by the Roddier test.
With Zerodur primary it should not be a problem even for a large planetary scope. The attached image shows the boundary fans still in place.
Quote:
Originally Posted by Atmos
I know a good number of planetary imagers that use a newtonian have boundary layer fans for the primary. Would you expect the same issue?
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Yes, I would definitely expect the same problem when the ambient temperature is dropping. However not blowing away the boundary layer may result in poorer images. A planetary scope needs to be designed very carefully regarding thermal issues.