In addition to the dew heater controller, an electric heating element is needed. The heating element is wrapped around a camera lens and gently warms it to prevent moisture from condensing on the lens.
Nichrome wire will be used as the heating element. This wire is very effective at converting electric current to heat, and is used in many common heating devices. Check your hairdryer or toaster, they use Nichrome wire to produce the heat. These devices are admittedly much, much more powerful than is needed to warm a delicate camera lens, but the same principle applies.
How Much Power?
This is a tricky question. The size of the lens, environmental conditions, and required temperature increase are all factors that will determine the power requirements of the heating element. Because most of these factors can’t be determined, I’ve designed the Dew Heater Controller to provide a level of adjustment to the heating element. The controller will modulate the power from zero to full power. With this, the heating element just needs to be powerful enough to provide the heat under the worst expected conditions.
A rule of thumb for camera lenses is to use 0.3 watts per cm for the heating band. Based on this, a heating element of about 5 watts should suffice for my needs.
Dew Heater Design
The simplest design is to have nichrome wire span the length of the heating element. The wire will need to have multiple lengths/passes depending on the power requirement and the length of the element. For the 5W heater, I calculated 5 passes of 30AWG nichrome wire were needed.
An inline fuse is used to prevent overheating if the element short circuits.
Assembly
Polyimide (Kapton) tape is used to electrically insulate the nichrome wire. The tape secures the wire and prevents it from moving around and potentially short-circuiting. This tape is capable of handling high temperatures, so it won’t degrade or become gummy with heat.
Copper wires are soldered to the nichrome element, an in-line fuse and a connector are added. This essentially completes the assembly of the heating element.
A fabric case to hold the element to the lens and help insulate the outside surface will finish the dew heater.
