My astronomy project:
Making of a heating band or dew heater
1: Introduction to making a heating band
This miserable condensation on the front lens! What to do about it? Built a heater band! Other names of it are Dew heater or Heater strip.
Out and look for suitable material to the mantle. Boat accessories, car accessories yielded nothing. Later I found a sleeping mat in black.
This will probably last for my telescopes lifetime.
A moderately large piece was cut for the 165mm lens.
Transformation to the cylinder shape by tape, the tape must be replaced with a higher quality before the test in the cold to be made. This cylinder has the dimension 150 mm long and 110 mm of it extends beyond the ordinary lens hood. The front lens has a diameter of 60 mm and the dew shields inner diameter is 75 mm, should be enough. This lens is made for the medium format film size of 60x70 mm in contrast to the small full frame 24x36 mm camera that I have.
Dew shield off.
Dew shield on.
I have ordered components to build a heating element as well, so there will be both hood and heating band for safety. The black plastic was handy to work with, only to remark is perhaps that it was really dull on the surface. The heating element I chose to build by myself to get it tailor-made for this lens.
The day after I ordered the resistors they showed up in the mailbox, 100 parts of 470 ohms. To this dew heater, it takes 10 parts and gives a resistance of 47 ohms when they are connected in parallel and a power of 3 to 4 watts at 12 volts. The cost 0.022 Euro pieces!
Fix the ten resistors at equal distance on the 27 cm distance corresponding to the perimeter of the front of the lens.
Cut and strip the cable that feeds the resistors. All resistors are connected in parallel.
Insulating tape so that no live parts is in contact with the metal parts of the lens.
An extra touch was to connect an extra outlet for more accessories to be connected in future.
2: Attach heater to dew shield and cables
Dew heater. It goes forward, now heat element tape mounted inside in the dew shield.
Here attached heating elements against the insulation in the dew shield, regular duct tape used.
The power is a little over 3 Watts which I wrote earlier. Now when the elements are mounted so there is a small risk that they overheat, the insulation makes the cooling effect limited. So should not be powered on during warmer weather.
Mounted on the lens and the equipment has been completed with one more connector. The idea was to test it during yesterday evening, but the weather put a stop as usual.