Dew Defeated

In an earlier column I reported my frustration with dew when I attempted to capture meteors along the Pacific Coast. I have had problems with condensation before – notably when in the North Coast of California on a vacation with my wife.  The skies were relatively clear, but the humidity was very high and there was so much ground level moisture the lens was covered in dew within minutes. Indeed, the moon above and the streetlights below led to this:

Earth vs Sky [5_020297]

Photo 1: Dew destroys an exposure.

Interesting, but not at all what I wanted. I was so desperate to get a good star trail while we vacationed near Point Arena, that we drove up to a Fort Brag, California,  Radio Shack and an Ace Hardware store so that I could purchase all the items I needed to build a  heater.  I had done all the math, so I knew that I would need at least a dozen resistors (200 Ohm, 1/2 Watt) for a heater powered by my big lithium battery (7.4 volts), or about a dozen 1/2 watt 390 Ohm batteries if powered by my 12 volt battery. I bought both plus wire, weather stripping, some tools, duct tape and velcro.  Unfortunately I also bought a thoroughly underpowered soldering iron and was unable to build the unit in the field due to flimsy cold solder joint.  My total outlay was about 40 dollars for all the components, tools, etc.   When I returned home I got out the GOOD soldering iron and completed the job.

BUT, you knew there would be a but, right? I was skeptical about using my home brew heater without something to protect my battery from over discharging. Lead acid batteries hate being completely discharged. Lithium batteries are not happy about that either. So I did TEST my unit briefly and was happy that it could work… but I never actually used it and even forgot to bring it on the night I needed it most.

So I BOUGHT a solution instead. The “Dew-Not“.  All that trouble I spent building a heater element was needless as the $22, 13 inch long DN004 heater does the job quite nicely and it fits my 82mm lens quite well.  I also ordered the priciest part of the solution, a $135 DNC2 controller which has under and over voltage protection and can be used to adjust the amount of heating (over heating is just wasting energy). I also got a DN003 (shorter) heating strip for my smaller barrel lenses.

I tested the Dew-Not unit out in my back yard during the following meteor shower – literally on the night the Dew Not arrived. I set the unit up at about 2 am and let it run until 7 am on medium. The ground and the camera were soaking wet from dew but the lens was clear and dry and it drained less than half of my 12V battery.

Photo 2: Dew Not 2-Channel Controller

The down side to this unit is that it does require a 12 volt supply – so only my HEAVY battery solution really works well with it.  And of course there are extra cords and such.  With a 12 volt battery it produces 6 watts of heat. With an 8 volt battery it would produce almost 3 watts which is still plenty except for the most humid nights. But when the humidity is close to 100% no solution will work!

Happy photons!

One thought on “Dew Defeated

  1. Steven Christenson

    I mentioned it in my prior article, but a simple, cheap and somewhat effective anti-dew strategy is to use those little hand (or foot) warmers that are air activated.

    Be careful, however as the active ingredients in those warmers are charcoal and iron filings. You don’t want them to come apart and spill into your optics or camera. I usually put my warmer(s) in a sock and tie the sock around the end of the lens. When it’s super cold, I’ve also been known to drop a handwarmer in a small insulated bag in which I put my Camcorder batteries that power my camera.


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