Newtonian vs SCT thermal handling with full aperture D-ERF

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Re: Newtonian vs SCT thermal handling with full aperture D-ERF

Post by LTHB » Mon Feb 03, 2020 9:11 pm

Very interesting thread, Marty! I wasn't really sure after reading your description of the problem and your experiments if you could measure somehow if the Baader red filter gets warmer in the Newton - maybe only part of the filter, as Mark suspected?

Anyhow, looking at the transmission curves of the ARIES ERF and the Baader red filter shouldn't it be possible to prevent part of the red light from reaching the camera by replacing the Baader red filter by an h-alpha filter? The narrower the h-alpha filter (35nm, 7nm, 5nm, 3.5nm) the better the camera should be protected from the heat - and a filter with, say, 3.5nm FWHM should hardly transmit enough energy to heat up a camera notably - or am I getting something entirely wrong?



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Re: Newtonian vs SCT thermal handling with full aperture D-ERF

Post by AndiesHandyHandies » Wed Nov 11, 2020 1:05 pm


Do the anti-reflection coatings on the SC corrector plate also reflect UV and IR?

RodAstro says lots of telescopes are not suitable for IR imaging bcause of the modern coatings on lenses doing this.
And also far blue like CAK.

Cheers. Andrew.

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Re: Newtonian vs SCT thermal handling with full aperture D-ERF

Post by RodAstro » Fri Nov 13, 2020 3:20 pm

Hi Marty

As Andrew says some AR coatings are restrictive ether end of the visual scale but this is normally done on refractors to make them appear better than they are, that goes for archos, EDs and triplets. I am not sure if celestron would be doing that on the Edge because the blue end of the scale is not so good?
MGf coatings are supposedly the best for Cak and spectrometry as it has little effect on spectrum throughput.

My experience of using a newt for white light was with my 10" open tube with full coatings. I made a 50mm symmetrical eyepiece out of two air spaced objectives and used a prism after the eyepiece to project a 12" image down to the back of the tube onto a drawing screen, I had no seeing problems with seeing and would leave the scope tracking for many hours over several years. The scope is still going strong in a club observatory with the same optics that are as good as the day they were made.
If your coatings are good virtually no heat will get to the glass 90+ percent is reflected.

As has been said try spacing the front ERF forward to let the tube breath.
Then, if it is for Cak imaging use a Baader blue imaging filter as your secondary ERF as this will remove the IR where most of the heat comes from.

Another thing to look at is, is there any plastic in the newt, primarily inside the focuser, SW use plastic to hold the bearing wheels in their crayford focusers, if you rack the focuser out far enough you will melt it.

Hope this is of some use Rod

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