In a message dated 7/9/98 4:27:39 PM Eastern Daylight Time, image66@xxxxxxx
writes:
<< BTW, anybody got any solutions to fogged lenses when shooting sunrises? If
your equipment is cold (as it would be if you started shooting while still
dark) it will fog up and moisture will condense as the morning air warms. >>
Actually, the problem of fogging (dew) occurs because the temperature dips
BELOW the dew point, and since it's not only darkest, but also coldest, right
before the dawn, condensation is most likely to occur at that time. This is a
common problem encountered by amateur astronomers, who use things called dew
caps over the front elements of their telescopes to prevent it. Essentially
they are just long lens shades. I'm not sure I understand the physics, but I
think the long cap prevents air circulation across the front elements. As more
air circulates, it brings more moisture with it (this is conceptually similar
to the refrigerated film thread we've been reading - leaving the canister
closed prevents additional air and moisture from making its way to the
surfaces).
A lens hood should help a little if you're photographing at dawn. Use the
longest hood you can without vignetting(sp?) the image.
If you're using long lenses, you may want to check out a telescope dew cap.
Take a look at Orion Telescope and Binocular Center (http://www.oriontel.com).
They have dew caps that wrap around and close with Velcro - some of the
smaller models should fit most moderate aperture telephoto lenses, I would
think. Another trick used is to warm the dew cap very slightly - this will
prevent condensation, but if the lens gets too warm it can cause aberrations.
Only a very slight warming (a degree or two) should be necessary. Orion has
heated dew caps, but only for larger aperture telescope, I believe. Some kind
of a heated lens hood would be ideal, and would probably work even for wide
angle lenses. Maybe there's an inventive photographer out there who could rig
something up with a hood, heating element, and some batteries?
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