Lens fogging during night time

[tiago silva]

Last weekend I made an attempt to photograph roosting Eurasian cranes

(Grus grus) in a riverbed by full moon. Preparation included

finding the bird's roosts, learning how to get to the shooting place

without making noise, film and exposure testing, etc.

 

Unfortunately the humidity was high and although the equipment was at

ambient temperature (5-10:C) the lens kept fogging making exposures

longer than 3 minutes impossible.

 

Can anyone tell me of techniques to fight this problem? Are the

anti-fogging sprays used by spectacle wearers adequate for photo

optics? And does it work?

 

P.S. As the Eurasian crane is a wintering species in Portugal, the

next adequate weekend will be in November.

[bobatkins]

It can be a problem in astronomy too - telescopes fog up. The

solution there is to use a gently heated lens hood. This is VERY

slightly heated above ambient using a battery and a heating element.

Too much heat and you'll cause air currents that degrade the image.

[vince_farnsworth1]

As Bob said, this is a common problem with astrophotography, mostly with scopes having large amounts of unprotected glass exposed to the air. The easiest way to avoid fogging is to use a lens hood. The hood should be as long as possible so that the glass is well shielded. With long lenses, this should be no problem. I use about an eight or ten inch felt-lined hood with a 500mm telescope and have never had a fogging problem. You may have to make your own. Be careful to keep the lens very clean and don't point it straight up. If these tips don't work you may have to resort to lens heaters or battery-powered hair dryers made for this purpose. Check out an astronomy catalog like that from the Orion Telescope Center (they may have a URL).

[badris]

Vince (and everyone else), the URL to Orion Telescopes is http://www.oriontel.com. You can also get cool astrophotography related equipment there, but I digress...