Oh no... Dew

[Matty P (Matt)]

After a few nights of heavy dew forming on the scope. I am seeking a cheap and simple way of removing or stopping dew from forming.

Any suggestions?

[trader10]

Hi Matty,

Oh no..... Hope it works...

..."

apply a low power hair dryer along the body of the
cell in a sweeping motion [DO NOT APPLY TO THE LENS DIRECTLY!!]. This should heat up the air inside the cell and
should remove the dew on the inside lens surfaces."....

http://www.astronomia.org.gr/cltlscp2.pdf

You can always take it to a astronomy shop but it will cost...

cheers

[acropolite (Phil)]

Might sound like a stupid question, but do you have a dew shield? Even the cheapo plastic models (e.g. Orion flexishield) do a fantastic job of keeping dew at bay. If you go with the hair dryer (12 volt from marine suppliers are the go) make sure you're careful, too much heat and you cook the coatings.

[Matty P (Matt)]

I have a dew shield and it works very well but... after an hour or two dew starts to form.

A 12 volt hair dryer sounds like it will work except I don't like to sound of cooking the coatings.

Is there another way?

[turbo_pascale (Rob)]

ASSUMING YOU'RE TALKING ABOUT THE FRONT OF THE OTA, NOT THE TUBE RIGHT???

Heater strip & controller around the front of the OTA.

For your scope: https://www.bintelshop.com.au/Product.aspx?ID=7210

Bintel used to sell Orion heaters (cheaper than the Kendrick), but perhaps not available any more?

You could buy the controller, but it's quite expensive. There are plenty of websites that have a DIY solution (I did the resistor chain version, and it worked, but it was a bit clunky for me and decided to just buy the strip in the end). The NiChrome wire solution is probably much easier.
http://www.dewbuster.com/heaters/heaters.html
http://www.simcoeskies.com/dew/no_can_dew.html

You can generally run these things directly from 12V, but you end up wasting the power quickly and heating up everything un-necessarily. The trick is to keep it just above the dew point.

There are a number of designs for DIY controllers (one I remember reading about was a PWM controller using a motor controller from Dick Smith). In the end, I was lucky enough that Andrew Johansen built me one, but you could start off with the strip and a 12V source (could be from a DC power supply rather than a battery).

The hair-dryer approach is after the horse has bolted. The heater strip will stop the dew from forming.

Turbo

[stringscope (Ian)]

Hi Matty,

All the bits are available from Jaycar in Canberra, just have to "stick em" together. Couple of images of a dew heater element being made and a complete dew heater contoller and heated (and illuminated) 50mm finder. The controller has a 10A capacity. Your 8SE will need about a 15W heater for the front corrector so the current drain will be a bit over 1 amp at the maximum heat setting.

If you need a hand, send me a PM.

Cheers,