Quote:
Originally Posted by Paul Haese
That is quite interesting Dave, as I had gradients a lot with the GSO Newt too. I put that down to more light in the atmosphere from Adelaide and suburbs or because the there was not a front shroud. I never once considered this might be a problem because the fans were on and drawing air over the primary. That is supposed to keep dew from forming.
Perhaps the primary being a conical shape contributes with excessive cooling which pushed some parts of the primary below the dew point after a few hours with the fans operating. It might also only occur in areas of high dew too. What is your dew like each night? We have heavy dew generally each night at Clayton and moisture laden air would perhaps contribute.
I'm reluctant to put any heat into the primary as this can set up tube currents and movement of the primary if the heat is too high, not to mention how do you use a primary heater on a conical shaped mirror? Perhaps just turn the fans off after a few hours and see what happens. Have you tried that?
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Hi Paul.
Yes, the nights have been of high dew although the mirror is never heavily dewed up. In fact the fogging is easily missed unless you shine a light on the mirror. I might try the easy option first - Turn off the fans and see what happens.
I noticed when only half the mirror was lightly fogged that this corresponded to an image that had a light background on one side of the image and a dark background on the other half. The image beforehand less so and the images before that were fine. So as the fogging increased the gradient increased.
Yes, I dont really want to apply heat to the main mirror and a conical mirror would be a challenge. I know AG Optical use such a system on their iDK scopes.