MadSci Network: Astronomy |
I probably don't have to tell you this, but for others who may read this, the reason your lens is fogging up at night is due to condensation. Water vapour in the warm air touches the colder lens and (according to the Particle Theory of Matter) the water particles lose enough energy that they change from a gaseous state to a liquid one on the lens.
There are two easy ways to solve this problem, as long as the lens is only fogging up on the outside.
If the outside of the lens is fogging up, you can try wiping it with a solution made of equal parts vinegar and water. If that doesn't work, increase the concentration of the vinegar. Alternately, one can buy many commercial products that prevent lenses from fogging up. They range from liquid sprays or solid waxy sticks to special cloths. These are commonly available in Canada (where I live) but I don't know about their availability in Israel.
The other way is simply to store your telescope in a warm, dry location or to store it in a location where it will be exposed to the air temperature (but protected from dust and sand and excessive heat which may warp the lenses). This minimizes the temperature differences between the lens and the night air.
Some advanced astronomers have told me that they wipe their lenses with silica gel, like the kind that comes packaged with running shoes. This keeps the outer lenses dry by absorbing moisture before it has a chance to condens on the lens.
Unfortunately, if the inside of your lens is fogging up, it is because there has been moisture trapped between the interior lenses. Many telescopes have sealed cases which prevent this, but once the case has been cracked or opened, moisture gets in between the lenses. In this case, I don't know of any easy way to keep them from fogging up. The advanced astronomers I contacted fill their telescope casings with nitrogen gas, which pushes out water vapor and (as long as the seal is kept) prevents internal fogging. However, most of these astronomers use telescopes with mirrors and refractive lenses. These are a little more expensive (but easier to make yourself) and don't tend to fog up as much.
Try the links in the MadSci Library for more information on Astronomy.