Although I've had the parts for this big scope for over 20 years now, including the spider and secondary holder, I think I may opt for a new secondary holder/spider from Protostar, and purchase the optional built-in heater. Very clean design: http://www.fpi-protostar.com/options.htm I've heard that the Protostar secondary holders are much easier to adjust than the older Novak designs that I've favored in the past (which are no longer available), so that's a bonus as well. Bryan Greer recently dropped his line of Pyrex diagonal mirrors completely in favor of fused quartz exclusively. The quartz mirrors should show essentially no deformation from the gentle warming of a dew chaser. Remember that a good dew or frost preventer merely raises the temperature of the optic above the dew point- it doesn't make the optic warm to the touch so there should be no induced distortions from differences in air densities close to the optical surface. You know, Michael, I've never had a dew or frost problem on anything but eyepieces- and then only when I place my eye close to it. A small chemical hand-warmer, which come in the form of a bag, solved the problem. They last for hours. You just shake it to mix the ingredients and start the catalytic reaction that generates the heat. Rubber-banded around the eyepiece, the problem went away. On all-nighters, I would cover the scope during occasional breaks and I think that helps as well. I'm sure our average humidity out here is much less than that of New England. Ever see a swamp cooler in Boston? --- Michael Carnes <MichaelCarnes@earthlink.net> wrote:
Back in New England, either a dew strip or a hair drying was a standard part of the kit if you had a refractor or SCT. On large reflectors, I tended to see heaters on the finder scope and the eyepiece..
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