Home made heater for dslr lens

Finaly, a clear night to make a star trail.

Unfortunately, the last experience was disappointing : the dew arrived earlier than expected and ruined most of the shots.

Only one hour to find a solution ?

No problem : I have a bike brake cable, double-sided Velcro tape and some cables.
I can built a anti-dew heater for my fisheye dsrl's lens...

One of the 0.3mm diameter x 1.2m long wire of the brake cable is used : it is the resistor that will produce the heat.
The wire is made of stainless steel, that is known for its electric resistance.
It will be connected directly to a 12V powertank. A preliminary with such a wire (same length : 1.2m) produced a soft heat, arround 30°C. A shorter wire produced an excessive heat.

As my pultimeter is out of order, I couldn't measure the resistance of the wire. I will as soon as I purchase a new multimeter.

I sewed the heating wire on the "soft" side of a 50mm x 300mm double-sided Velcro tape (passing the wire in the loops).

A second double-sided Velcro tape sandwiches the heating wire and helps hold it in place.

As the stainless steel can't be soldered on a copper wire, I made a mechanical connection with a domino.
The domino is sewed and glued on the tape.

Overview of the heater, with a 1.5m long power cable and a ON/OFF switch :

Views of the heater in place on the Samyang 8mm fisheye lens :

On these pictures, one can see the difference between

- star trail without heater : short sequence and blur due to the dew,

- star trail with heater : long sequence,without blur.

Conclusion :
Manufacturing in a very short time (1 hour) of an efficient and safe heater (around 30°C).
This solution makes possible the manufacturing of different size heaters.