Refractor below zero

I am going to using a refractor with temps below zero. What effect will the temperature have on the scope? Should I use dew heaters? Etc..Etc...rowland

Rowland Hamly said:

I am going to using a refractor with temps below zero. What effect will the temperature have on the scope? Should I use dew heaters? Etc..Etc...rowland

The glass doesn't care as long as the temperature changes (especially cooling) are gradual. It would be a big mistake to uncap a room-temperature lens at -5F. The design of the metal lens cell is also important, some can handle extreme temperatures, and others will deform or pinch the lens.

Dew heaters are a good idea if the dew point is within 15F of the ambient temperature. If you bring the scope inside a heated space after observing, keep it in its case or wrap it so it warms gradually. A cold lens will frost over instantly in a warm heated space.

And when bringing the scope back indoors after a cold nights' observing session, reverse the process, covering lens/scope while still outside before moving it inside. My problem in such frigid near zero conditions was unequal metal contractions/expansions; dissimilar metals in contact can cause one to break. So perhaps reduce screw tension adjustments from their normal indoor or temperate climate settings.