Quote:
Originally Posted by mental4astro
Andrew,
Black is black and it will create thermal and dew problems - but if you are having good results with it without dew issues, good on ya!  By the look of things dew may not be a problem for you - you lucky bugger!
Alex. |
Thanks for your very detailed response Alex. I only upgraded my OTA a few months ago from a 6" Evolution SCT (which is actually painted silver) to my current C9.25 SCT which is painted black. I had previously used a black foam rubber dew shield on the 6" to good effect, and the one time I've needed to use a similar shield on the 9.25" it worked fine, no dew to be seen. To be sure, the black foam was damp with dew, but the corrector plate was clear.
Regarding the OTA cover, I don't have enough experience with my 9.25 to say one way or the other whether the black foam cover is helping or hurting the tube currents. I didn't use anything on the (silver) 6", just set it up early and waited a couple of hours to equalise. With the 9.25, the planets have been so low (and dropping fast) that the images I've taken of them were not made under ideal conditions (which would include tube currents), but I've had some success with
Saturn recently.
As luck would have it, I have some large sheets of white Corflute here at home in both 5mm and 3mm thicknesses, a free weekend, and a good weather forecast for Monday night with Neptune and Uranus nice and high in the sky. It also looks like dew wont be problem as the dew point is supposed to be 6* lower than ambient. I'm assuming the 5mm Corflute will be better than the 3mm, a little extra insulation will help there. I also assume I will still need to blacken the inside of the dew shield section to remove stray light reflections, or maybe at the moment I'll just use the foam rubber shield I already have. I think I'll make the dew shield separate from the OTA cover.
Thanks again,
Andrew