Heated dew control advice

[bcfcciderhead]

After last nights cold observing outing i think i'm leaning more and more to some heated dew prevention tape, the ice on the OTA helped with this.

I have a home made dew shield (camping mat) which is ok but when out in frosty nights it's not enough.

What i need to know is what do i need to get?,

It will be for my 200P so of course an 8" length of dew tape for the OTA, if this is fitted up near the EP (sec mirror) will this work well enough to stop dew forming on both the sec mirror and the EP? or will i need to get dew tape for the EP? if so what size 1.25" or 2"?

I understand in some cases these can be powered direct from a power tank via a fused 12v car cigar lighter plug to RCA or phono lead, Would this be ok? or would the need for a dew controller be better?

[swamp thing]

Hi Dave

The heater tape needs to be around the edge of the secondary itself to be effective.

You need to wrap it around the edge of the secondary mirror (obviously taking care not to touch the mirror)

Find out what size you need first by wrapping some string around it then measuring it.

I find this system very effective indeed.

The eyepiece lengths of heater tape will suffice for both 1.25" & 2" eyepieces.

If you are going to invest in this system you may as well get dew bands for the finder scope as well.

Regards Steve

[umadog]

You will need a controller. Using the 12 V directly will produce too much heat. The secondary is hard to heat correctly: if you don't insulate the heating device in some way then you will end up heating mostly the air around the secondary which will cause dreadful tube currents. You'll see the heat-plume if you de-focus on a bright star. Eyepiece heater strips should have insulated backs, so wrapping one of those around the secondary, as Steve suggests, could be a good way to go. I've tried gluing resistors to the back of the secondary with thermal epoxy and that produced a vast heat plume.

[bcfcciderhead]

thanks guys, i thought the heater strips went around the OTA near the secondary mirror, something else i learnt

[umadog]

You're thinking of an SCT, where the heater strip does indeed wrap around the front of the tube because you want to heat the corrector plate. A Newtonian doesn't have a corrector plate, so you don't want such a heater strip.

[bcfcciderhead]

Thanks umadog did not know that.

I been looking at these, are these what i need? once i know what size secondary mirror i have.

First Light Optics - AstroZap Dew Heater Tapes

and this controller

First Light Optics - HitecAstro single-channel, dual-port Dew Controller

[swamp thing]

That's the kiddies.

I would go for a multi point controller so you can use more strips to prevent dew on eyepieces etc.

Regards Steve

[umadog]

These are really good: DewBuster although not cheap. They're super well made, though, and you have a solid warranty with excellent customer service. Even if you don't want to pay that much, have a look around the site. There's info on making your own heater strips and links to pre-made ones. Looks like you could save a fair bit buying strips from the US.

[bcfcciderhead]

thanks again guys, very helpful, will gives this ago.......thats my christmas present's sorted.

[faulksy]

i made my own heater controler and dew strips using this nichrome wire.

eBay - The UK's Online Marketplace

works a treat still trying to sew though lol