Hi all,
Following on from my experiments and success with using fans to control dew formation on SCT's and Maks, I got to thinking "well, why not refractors too?".
I guess the mental block here is fracs come with a ready made lens shade/dewshield, which for some reason most of us feel this cap is mandatory to use and cannot be removed under any circumstances.
Well, say's who this is the case!?
Why must the original lens shade be used?
And with many lens shades being painted black on both the inside and outside, it is PREDETERMINED that it will be a dew magnet.
And again here we go sticking heating straps on the whole thing, pumping huge amounts of precious electrical energy into a metal tube which only transmits a small amount of this energy into the glass, and most is lost into the heat sink that is the metal tube.
There is an alternative that uses bugger all energy in comparision
A heat free dew control solution.
The manufacturer supplied lens shade is the main problem here. So, first step is to overcome this mental block that IT must be used all the time. Being made of metal, and that
at least one surface is painted black, these lens shades add to the dew problem.
So, pull it off, put it in the scope's case, and make a new one. One that you can cut into.
Second, once the new shade is formed, cut a flap into the side, approx 100mm in front of the objective, to accommodate a 40mm X 40mm 12V fan. The flap is not totally cut out, but one side is left to hold the fan in place. The way the fan sits in this slot the air it blows into the lens shade will create a vortex of air that will dry off any dew that's formed on the objective, and keeps it from forming, in the exact same manner as I described in my earlier piece -
SCT & Mak total dew control without heat - a solution!.
I made this new lens shade out of Coreflute. I lined the inside of it with black felt, and it stays in place with Velcro spots and a Velcro strap. Thing weighs significantly less than the original metal lens shade too. Every second cell of the outside surface of the Coreflute is cut so that the thing will easily wrap around the objective.
I also added a small PWM unit to regulate the revs of the fan, low or high, as I feel is needed on any given night.
If the night is not a dewy one the original lens shade can be left on, or the lighter weight one can be used with the fan removed and the flap closed.
No heat, less power, a lighter weight, and a dew free objective.
Thanks for reading,
Alex.