Dew an issue on a StellaLyra RC?

[Hughsie]

My experience to date has been imaging with a 4” refractor but now I am considering stepping up the aperture and I am very tempted by those naughty people at FLO to buy a StellaLyra 8” RC (subject to my good lady’s permission). My question is dew and how to control it? Are there issues with the primary and secondary mirrors fogging up? If so how is that controlled? I use dew straps on my refractor and guidescope but I am scratching my head on how a similar approach would work with the SL RC.

[johninderby]

With my TS CC dew is not a problem normaly so would expect the same with the RC. Would have to be really wet for any dewing.of of the secondary. I’ve had water running off the outside of the tube but no dewing up of the mirrors.

You can get heaters just for the RC though.

https://www.kendrickastro.com/rcoptics.html

Edited October 16, 2020 by johninderby

[vlaiv]

Happened to me only once - very damp conditions, but I did get some dew on secondary.

[Xsubmariner]

  I have a 10” RC and fitted a heater element to the secondary mirror base and have a large dew heater wrapped around the body in line with the primary. You will need to re-collimate the scope if you fit a secondary heater. My advice is to pay for a secondary heater at point of purchase, hopefully Your supplier could then fit one and re-collimate before delivery. You may be lucky where you are that you don’t suffer dewing, mine did so I had to fit a heater.

[ShrewView]

I've had my 8cc out a couple of times now. The first was a pretty damp night with lots of dew on the outside of the tube after around an hour or two and the finder was completely dewed over, but there was nothing on the mirrors.

I'm guessing dew straps would be a good addition if you're planning a long session in this climate though.

[Nik271]

Telescopes lose heat at night chiefly by radiating it into space, So the part which gets coldest is the one facing the sky. This is why the correctors of Maks/SCT get dewed up so quickly.

In open tube designs the secondary is protected in it housing and is pointing away from the sky so it will be very unlikely to dew up. The primary will almost never dew up. 

In winter I tend to use my C6N Newtonian and it has never dewed up.

Clear skies!

 

Nikolay

 

Edited October 16, 2020 by Nik271
corrected typos

[Nik271]

PS. I forgot to say, that I rarely use my telescope for more than 2 hours in winter, as I mostly do visual, so my experience may not be relevant for  imaging which can take the whole night.

Eventually every part of the scope will get cold and once it reaches below  the dew point of the ambient air it will dew up irrespective where it is.

Nikolay

Edited October 16, 2020 by Nik271

[Hughsie]

Thank you everyone for your responses. Much appreciated.

[vlaiv]

44 minutes ago, Xsubmariner said:

  I have a 10” RC and fitted a heater element to the secondary mirror base and have a large dew heater wrapped around the body in line with the primary. You will need to re-collimate the scope if you fit a secondary heater. My advice is to pay for a secondary heater at point of purchase, hopefully Your supplier could then fit one and re-collimate before delivery. You may be lucky where you are that you don’t suffer dewing, mine did so I had to fit a heater.

Is your 10" RC truss design or solid tube?