dew heater strip on newton?

[Gerhard]

Hi all,

just a quick question:

saturday night I was out observing, and towards the end of my session it got so humid, my primary mirror had dew droplets on it... (150/750 Newton)

Should I be looking at buying a dew heater strip, or should I follow what others write: "if your newton primary fogs up, it's time to go home"?

Thanks!

Gerhard.

ps. btw the dew produced some interesting haloes around bright stars! :-DD

[Charic]

Gerhard.............If I'm mobile away from home its time to pack up, as the Stars will still be there next time. The last time away I experienced any issues, everything was actually freezing around me, even the car?

I have an extension to my Newtonian made from  camping foam underlay. They say 1.5x the diameter of the aperture is sufficient, and mainly to reduce dew on the secondary mirror. If the dew is all over the primary, give up, or have install a PC fan?

What I think I have noticed with the extra length is a reduction in stray light from the street lamp.

[Tinker1947]

Did you have a dew shield on the end of the scope....

[laudropb]

+1 for the dew shield. Since getting one for my 200p Dob I have had no problems with dew on primary or secondary mirrors.

[Gerhard]

Did you have a dew shield on the end of the scope....

No. Usually, in fact, I have no dew issues. That is, the tube gets wet, but the mirrors stay clean, usually... But maybe a dew shield could come in helpful....

[Charic]

.......my primary mirror had dew droplets on it..

..... I have no dew issues.....

.........the mirrors stay clean, usually........

Confusing, but if its just the OTA (optical tube assembly ) you could wrap some thermal insulation around it, similar to the self adhesive stuff you can place behind wall  radiators.