Is a Dew Shield just a Dew Shield

[AlistairW]

Hello,

What other purpose does a Dew Shield do ? - I have a heated band around my objective so do I really need a Dew Shield, or, does help as to stop 'stray' light coming in at oblique angles to the OTA ?

Thanks

Alistair

[michael.h.f.wilkinson]

I generally prefer using just the dew shield, rather than a dew band: it keeps my power supply going for longer if I am in the field, and I am (probably needlessly) worried that I might be causing thermal currents. A dew shield will of course keep some stray light out, but that should really only be an issue with the moon, I would guess

[Adrian Condon]

Hi Alistair,

I use both a dew controller Kendrick Digifire 7, with dew bands. By using the bands on the lowest setting seems to conserve energy.

I have made a dew shield from camping mat for my dob, this seems to keep the dew off the secondary mirror. I have a fan and dew band on the primary as well. I agree with Michael's comments on preserving power especially with batteries.

Incidentally, I use a bottle of Ouzo to determine when to switch the heaters on...... The ouzo goes cloudy as the dew starts to fall...

If no dew, then you could drink the ouzo......

I have recently purchased a Kendrick Digifire 12, this has temperature control facilities to measure the ambient and optics temperatures.

I have not had the opportunity to use it yet, planning to use it at the November Galloway Star Party.

Cheers

Adrian

[michael.h.f.wilkinson]

Like the use of ouzo. Drinking too much makes your head go cloudy, of course

[laudropb]

I've got a bottle of Ouzo in the cupboard, so must give this a try.

[xtreemchaos]

i think a dew shield adds to the contrast aswell. clear skys charl.

[chiltonstar]

I find a dew shield helps to reduce light scatter from any streetlights or security lights that are visible from where my scope is parked, as well as delaying the (inevitable) dew problems. For me, a heated dew band caused definite thermal effects when looking at double stars at high magnification, rather like those from using the scope on the driveway or patio rather than on grass (not a problem for DSO observing perhaps).

Chris

[cjdawson]

A dew sheild's primary purpose is help slow the progression of heat radiating away from the optics of the scope.  As a side effect of adding walls to the area in front of the optics, it helps to reduce stray light from entering the scope from acute angles.  Which means the contract can be improved.  It also helps to stabilse the optics as the air immediately inside the dew shield becomes more stable.

So overally, you get

1. Longer observing until misting occurs

2. A "slightly" more stable image dew to the pocket of stable air in front of the scope

3. improved contract dew to less stray light.

When used in combination with a dew heater it also means that the heater can be run at a much lower power, conserving energy allowing your power supply to last longer.

[Starfisher]

a dewshield is always a win as explained very well by cjdwason.

only look out when you buy one. see that the outside is made of decent water resistant material and that the inside is not finished by shiny materials like cheap plasitcs for example.

and the velcro's should be wide enough. ofcourse order the right size .

dewshields with some flocking material inside is good for the contrast and stray light.

or ofcourse you can make one by yourself. i think if you looking up for things like " diy dewshield " or things like that that you will get some nice links or try to find it at sites like youtube astroshed is a good place to look at if i am not wrong.