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|Re: Observatory Window?
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Posted by Dianne on January 15, 1999 08:47:27 UTC
: : : : No firsthand experience, but some comments and : : : : questions if you don't mind. What size / kind of scope : : : : are you using? What types of observing do you : : : : plan on? For a large scope, and mostly planetary : : : : views, you could probably get away with it. For : : : : deep sky observing of faint objects you're going : : : : to loose a lot of light - which gets costly REAL quick. : : : : Hassles are: reflection of outside surface, interference : : : : on outside surface from surrounding light pollution, : : : : thermals as you mentioned, and refelction from the inside : : : : surface backinto the scope. IMO, I'd go for a "small" : : : : opening, try to ven the heater to prevent thermals, : : : : but go with open sky... but that's me.. : : : : Let us know what you do!
: : : I've got an 8" Omcon and I'd like to do all types of observing, : : : at least until I have enough experience to know if I will have : : : a preference.
: : : I know open-to-the sky is the way to go but for the past week we have : : : had daytime highs around -24dC and lows around -31dC BURR!! - so : : : the scope has sat in the corner even though the night sky is : : : India-Ink black and the stars are incredibly bright.
: : : My thinking is thus - if you can make a lense for the front of a : : : refractor, why can't I have a "double-planar lens" in front of my reflector?
: : : I will probably build my obs so I can have a removable window. When : : : conditions or objectives permit, I'll use glass. For critical viewing, : : : I can open the window.
: : : : You will probably have to deal with both frost and condensation on the window, which will require sraping or chemical de-icers, which will increase the real problems you will have, which, as has been mentioned, will be loss of light and distortion. Another real problem, and on that has to be dealt with on the refractors you mentioned which do have a glass front(the lense) is cromatic aberation. As light passes through glass, not all frequencies pass through at an equal rate. This is what causes a "rainbow" with a prisim, and is why the refractor you mentioned as a three or four element primary lense. The multiple elements correct for the aberation caused by each of the others. Any window you use will not be corrected, and unless you are viewing in absolute alignment, (the light is traveling exactly in a straight line between source and the mirror of your scope, which is practically impossible, the window will cause some degree of aberation. This will be increased by irregularity in the glass.
: : As allready noted by others, the glass will also stop a great deal of the light. Glass is amazingly untransparent, which is why the glass on a refractor and on your oculars is coated. (The redish or blueish color on the glass is the coating.) Coating can greatly increases the quantity of light which will pass through the window, but having a window coated will also be very expensive.
: Seems to me that all the plausible solutions to your delima would be very expensive to do right. Since you would have to spend a good deal of money anyway, why don't you just go to remote viewing and stay inside!
Remote viewing is a definate possibility for the cold months. With an average daily temperature around -25 in Dec & Jan, I wont have any problems getting low dark currents on a CCD. Providing a heated enclosure for the "electronic accessories" and a little heat to keep the mechanics from freezing up isn't hard either.
Thanks for the suggestions everyone. Clear darks sky to all!
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