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Dew heater

Have you ever taken long-exposure photos of the stars at night? I‘ve done a little. I’ll do more now that the weather is warming up. During the colder months though the lens would fog up. And not just on the outside. Getting condensation *out* of a lens is not easy and takes a while.

This little project is to build a small heater to be wrapped around a medium-sized lens for a 35mm film camera. It will use a length of nichrome wire and a small battery pack to produce heat. A layer of neoprene rubber from a beer-can cooler will insulate the lens and heater wire.


  1. Nichrome wire
  2. 1.5mm green heatshrink tubing
  3. Powertech 2400mAH AA x 4
  4. 4xAA battery holder
  5. Jiffy box, 130 × 68 × 41mm
  6. SPST mini rocket switch
  7. Red and black 4mm banana right-angle plugs and sockets
  8. Red and black light duty hook-up cable
  9. 1A panel meter

Other parts

  1. One beer cooler


Link #1 (below) talks about building a 45W heater for the correcting plate on a 14" schmidt-Cassegrain telescope (SCT). Scaling down the area to a 60mm diameter camera lens (355.6² / 60²) gives about 1.28W. The configuration I‘ve come up with (spreadsheet) is 4 AA’s at 1.2V each, giving a maximum of 4.8V. With 6 turns around the 60mm camera lens, it should produce almost 1.5W. This should be enough power for a camera lens. Compared to a telescope mirror or correcting plate, a camera lens has a higher proportion of volume to exposed at the front.



Preliminary construction plans

A rough overview of what I plan to do:

  1. Cut open beer cooler. Cut the seam up the side and one around the bottom. Discard the bottom piece. Trim to fit desired lens(es).
  2. Place a length of the nichrome wire inside the heatshrink tubing and heat the tubing to insulate the wire and make it more managable.
  3. Bend the wire into a zig-zag pattern the right size for the beer cooler.
  4. Sew and/or glue the wire to the inside of the cooler rubber.
  5. Sew on velcro strips to the outside of the cooler rubber.
  6. Hook up power leads.
  7. Wire up jiffy box with the amp-meter, battery pack, and connectors.
  1. Hunters hill observatory 45 watt dew heater
  2. A do-it-yourself dew heater for an SCT
  3. Home-made heater strips