Quote:
Originally Posted by Camelopardalis
Btw, just to clarify, I wasn’t explicitly advocating a 12” newt, they are a beast(!), although Glen’s mount would be fine with it I’m sure.
My gut feeling is a little more mid-size, say a 10” f/5, as Glen already has an ASI1600 camera, which combined will give a resolution of about 0.6”/pixel.
May sound like a compromise, but an economical, easy(ish) to handle, easy(ish) to collimate compromise  |
Thanks Dunk, you may recall I had a 10" f5 truss Newt that I built some years ago, and used for imaging. It was pretty light, sadly I let it go (parted out in the end). Re a 12" I have considered buying the bare carbon tubes that TS sells and using a GSO 12" as a donor to build a light weight 12". The tubes are bored for GSO components. With an upgraded focuser it would be nice. Of course I could do the same with a 10". My worry about that approach is over capitalising something I will have to sell down the track.
Quote:
Originally Posted by mental4astro
Dew control is certainly a challenge for a corrector plate. But there is a change of thinking when it comes to dew control.
We seem to think that the only way of using a scope is to wait for it to cool, and then we stick a heater on the thing... I've always thought this was strange because of the thermal problems a heater creates... But that's beside the point here.
The new thinking is NOT to let the scope cool!
The problem of a scope cooling is not the heat per say, but the temperature differential that is created between the warm interior (mirror, baffle, cell), and the cold metal tube, and the heat plumes that are then generated inside the OTA.
So, if the heat differential is not allowed to occur in the first place, then the heat plumes won't be generated, the inside of the OTA is thermally stable, and you can start using the OTA immediately without waiting for the thing to cool.
I am not talking about keeping the OTA warm. Instead I am saying we should slow the rate of cooling. By insulating the OTA, the metal/CF tube is not allowed to get cold, and so the heat differential is reduced to the point where there are no heat currents being generated inside the OTA.
The insulative material is extended beyond the corrector plate of the SCT or Mak, and this acts as both a dew shield and an extension of the insulation to enhance the protection of the corrector. This won't totally prevent dew formation on the corrector in humid conditions, but it will extend the dew-free period, and if a heating strap is used it can be implemented sooner while the OTA is still warm, so to take advantage of the residual heat of the OTA so the strap is not needing to also heat a stone-cold metal tube at the same time.
Alex.
|
This is how I managed my MN190, it lived in the house and was carried out for any session, and went to work straight away. I used a foam yoga mat (black) as a dew shield with a heater strap underneath it to prevent corrector cool down. It tended to last all session without fogging.