Frozen Primary

[MattJenko]

I have a little RC6 and when out playing with it a few nights ago, after about 90 mins in the subzero temperatures, the primary froze over. What are my options to prevent this? I am wondering if a non heated dew shield is really going to cut it against a hard frost and if I may need to put some kind of heater over the primary end?

[Paul73]

I would try the cheap camping mat Dew shield approach first. If you keep the moisture off the glass, there is nothing to freeze (in theory).... When was the last time that the primary of your 250px froze?

Paul

 

[alanjgreen]

1. I would try a dew shield first.

 

2. Then you can add a heater tape if necessary.Normally, with SCT the heated tape keeps the corrector plate clear at the front. With a RC I guess the cold is either coming in from the front (dew shield will help) or making its way in through the back - can you insulate the mirror from the case at the back?

 

3. perhaps a newtonian "split secondary heater" could be attached to the rear of the primary?

- my new seconday is 113mm, nearly as big as your primary it has a kendrick heater stuck to the back!

http://www.kendrickastro.com/newtonian.html#Primary

[MattJenko]

Good point on the 250px, as the answer is never, although it came close once

It may just be me, but dew shields never seem to have the most secure of connections, and as I plan on using the scope for mainly unattended spectroscopy imaging, it will experience quite a bit of slewing around the sky over the course of a session. I do like the idea of a little heater behind the primary, might look into that, thanks. 

[Daniel-K]

29 minutes ago, MattJenko said:

I have a little RC6 and when out playing with it a few nights ago, after about 90 mins in the subzero temperatures, the primary froze over. What are my options to prevent this? I am wondering if a non heated dew shield is really going to cut it against a hard frost and if I may need to put some kind of heater over the primary end?

frozen mirror  never had one of them even when ive been in -15 temps did it dew over first?

[MattJenko]

It certainly wasn't -15, but I was pointing the scope near the zenith, so it did get the full open sky effect. Maybe another alternative is to avoid pointing the poor thing straight up

[johnrt]

I have never suffered from frosting or any dew on the primary ever, and I leave my 6" RC out all night in all temps and humidity, I simply use one of these, they are secure as they fit around the dovetails on the top and bottom of the OTA.

https://www.firstlightoptics.com/dew-prevention/astrozap-flexible-dew-shield.html

 

John.

[MattJenko]

Thanks John, was hoping you would say that.