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Old 16-12-2020, 04:20 PM
Saturnine (Jeff)
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If i may, I'd like to throw in a first hand, in the field, observation about the different effects colour has with telescope tubes and this was noticed on many occasions.
Several ( many ) years ago while out on observing nights with the astro club I'm in, it was noticed that my scope tube would be covered in dew while a fellow members scope would hardly be damp at all. Both scopes were old school cardboard tubed newtonians, my friends was a Meade dob, coloured white, whilst mine was a home made newt / dob, painted red.
So, as the materials of the scope tubes were the same and affected by the same environmental factors at the time, we were set up less than 5 metres apart, it could be construed that it was the difference in colours that was the governing factor in the dew formation on the telescope tubes.
If anyone has a better explanation I'd be happy to hear it. Sticking to white tubes these days but even they get dripping wet some nights, this is a very humid region after all so some price has to be paid for long nights in the field.
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Old 16-12-2020, 05:47 PM
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The_bluester (Paul)
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I know it is obvious that my refractor (White) collects less dew than my SCT (Black) and the refractor before it (Also black)

What would be an advantage in carbon fibre would be the thermal expansion aspect in the SCT. With two magnifying mirrors in the SCT design the shift of the focal plane as the mirrors are moved relative to each other is something like 25 X the change in distance between the mirrors. In practice the aluminium tube C925 shifts focus by hundreds of microns per degree of temperature change. If a carbon tube cut the thermal expansion rate of the tube in half that would be a pretty big advantage. And if cooling and gathering dew is a concern, loose the sexy carbon weave look (If it has been laid up well enough to look good) and paint it white.

I can say the SCT certainly changes focus rapidly, I set up my refractor on Monday night but I didn't bother with the SCT as the night was expected to cool by around 10 degrees, the SCT would be catching up to the temperature change for at least half the night. I know with a temperature gradient like that it can go from sharp focus to doughnuts in 20 minutes. And you can't just trigger focus runs by temperature change as the tube lags the air temperature. I end up with it doing 5 subs and a focus run every third or fourth one in order to keep it sharp.
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