Reusable chemical heat packs for fighting dew?

[VigdisVZ]

Hello SGL!

Since I experience dew on my DSLR yesterday when taking long exposures I realised I might have this problem with my newtonian that should arrive any day now. I was looking at electric heating but then it struck me that I might be able to use handwarmer heatpacks akin to this one (by strapping them to the scope).

Would this work at all? My idea is that it should if you take care to use some padding in between (or removing the pack if they become too warm).

Since I like having a bunch of these around I figured why not let the scope in on the cosy?

Greetings

[Stargazer33]

Hi Carl,

I used to use these early in the year when I used to dive (scuba) in a wet suit. I would pop one or two down inside my wetsuit just before I kitted up and rolled into the English Channel - 9-10 degs C! From that experience I can say that they heat up very quickly and get very hot! My worry would be that they would be too hot too quickly. If the scope was already cold and you put a couple of these around it, the sudden and rapid temperature change could cause distortion of the OTA. There is also the possibility of hot spots. Not to mention trying to hold three or four of these around your OTA whilst trying to secure them in place! But then I am thinking in regards to the corrector plate on a SCT or Mak rather than a Newt.

Bryan

[brantuk]

Bit heavy, uneven, and the heat can't be controlled - that'll give you all sorts of problems. Keep them as handwarmers and get a dew control system is my advice.

(possible cracked mirrors, distorted images, etc for example)

[VigdisVZ]

Thanks for the replies and warnings.

My idea was to use one, with some kind of material in between it and the scope as a buffert zone, and put it a bit away from the optics in hope that it would radiate enough of excess heat around the OTA to keep it clear. I suspected cracked and distorted optics could be a worst case scenario with this.

In any case I'll go ahead and see how the scope works naked before I invest in electrical heating, but I guess it's just a matter of time before I end up with it.

Once again, thanks!

[Stargazer33]

A good dew shield, either bought or homemade, makes a big difference to the amount and rapidity of dew formation. Lots of people on here make them from the firm foam camp mats that you can pick up quite cheap. If you haven't got one already I would certainly recommend that as a first line of defence. It also helps to block out any stray light from getting into the optics.

Bryan

[Velvet]

Would not advise these as the get hotter and hotter and may be not suitable for dew purposes. I know someone who got a nasty burn frm one of these when they fell asleep with it in thie poclet!!

Velvet

[Daniel-K]

to be honest if you strap it to the top of your dew shield on the out side as the heat currents rise it mite give you and extra hour before the seconday dews up. your scope will just become a little out of balance, wouldnt work if the scope was pointing straight up as the dew fell but any other direction it should be ok, if moneys tight experiment a little, wouldn't stick it by the primary though or on the steel tube as the currents would be a mare, oh and dew on the dslr just wipe it off thats all i do