Dew heater questions

[badhex]

Hello all, 

Managed a really great session a couple of nights ago and the weather played nicely with one exception: Dew! Loads and loads of dew! 

I do already have a 4-port lynx astro heater controller, two 50cm dew heater bands and a Celestron 7.2Ah power tank, but have rarely had need for them, so I admit I'm not super experienced in best practice. Initially, I did not set up with them, but after an hour or so of observing dewing became so bad that simply moving my eye away from the EP for more than 30 seconds meant it would be unusable. 

I hastily set up, but ended up losing probably 45mims adjusting and waiting for things to clear. The finder was a complete write off, but I did initially set up one strap to clear it, then capped it. I pretty much didn't use it for the rest of the session, only occasionally uncapping, observing quickly, then capping again. Not really very helpful for a finder! 

I had the band on the scope set to max, and used the other band in the case I'm using to keep EPs covered whilst not in the scope. It works very well actually, like a toasty little bed for the EPs to stay warm and dry. I might develop this into a more permanent solution going forward. 

Anyway, a couple of things I wondered about. Firstly, where is optimal placement for the band on a frac? Obviously it varies from scope to scope, but I placed mine where the objective is, which is actually on the dew shield (photo below). Whilst this seems sensible, it also means it has to warm up the dew shield and OTA before it even reaches the OL assembly. Would it be better on the OTA itself, which puts it slightly behind the OL? I noticed that once it's up to heat, dew was not on the OTA for at least 10cm so maybe it's more efficient on the OTA itself? 

Secondly, what power to use? I put it on full because the situation was bad, but running two bands at full whack did fully empty the battery during the session, and I'd assume that full power is not always necessary. I estimate I had it running for approx 5-6 hours, and according to the manufacturers specs I should get about 4h20m running at full pace. I guess it varies and the answer is as low as possible whilst still keeping dew free - but how do you know without potentially wasting ages figuring it out on the fly? Is there a method which anyone can recommend like heat on full until the dew is gone, then turn down to half and see how you get on? 

Lastly, do coastal areas have more of an issue with dew? Or places near woodland and national parks etc? I'm potentially moving to the Folkestone area so it's something to consider, whether I might need to invest in better dew control stuff at some point. 

Anyway, any experience folks might have would be interesting to hear! It's a new area for me as mentioned, and I'm always keen to hear from people more experienced than myself. 

Thanks! 

 

[wookie1965]

On my Tal I put the band on the objective and one just in front of that. 

Power wise I have USB bands 5v and use a power bank so I have no trailing cables I find these keep me dew free in my yard. 

[josefk]

I also don't have a load of experience with dew bands though i do use one on my bigger refractor.

I put mine just behind the dew shield (so probably around the lens cell more or less). So i can run it at the lowest power setting (and so leverage a small energy source for many hours) i put a short section of foil backed camping mat around both it and the dew shield extending the effective dew shield by a few cm by doing so. Seems to work so far. If i fear it is necessary to use it then i use it right from the off - i don't wait for dew to start to form.

I despise dew more than any other local impediment to observing. I like IP6x rated bird spotting optics!

 

[badhex]

5 hours ago, wookie1965 said:

On my Tal I put the band on the objective and one just in front of that. 

Power wise I have USB bands 5v and use a power bank so I have no trailing cables I find these keep me dew free in my yard. 

Cheers Paul. I've found quite a good place to put the heater controller as well and keep the cables out of the way thankfully. Interesting that you put two bands on - do you find it doesn't work so well with only one?

[badhex]

4 hours ago, josefk said:

I also don't have a load of experience with dew bands though i do use one on my bigger refractor.

I put mine just behind the dew shield (so probably around the lens cell more or less). So i can run it at the lowest power setting (and so leverage a small energy source for many hours) i put a short section of foil backed camping mat around both it and the dew shield extending the effective dew shield by a few cm by doing so. Seems to work so far. If i fear it is necessary to use it then i use it right from the off - i don't wait for dew to start to form.

I despise dew more than any other local impediment to observing. I like IP6x rated bird spotting optics!

 

Yes I think my biggest error was not to set everything up from the start, and that way I could have followed what you do and keep it on for lower and longer. The objective was actually fine for a whome but then I was viewing stuff at higher altitude and it just suddenly just fogged over completely. Interesting move with the foil camping mat - I imagine it certainly can't hurt! I have looked at those purpose built dew shield/heaters before as well. 

[josefk]

hi @badhex - the camping mat solution doesn't stop me also looking at proper dew shields with built in heaters because the camping mat is flimsy so is semi-consumable. But the big advantage of camping mat material is it is super light.

Here's a pic from the spring - this is at the end of an 8hr session. it wasn't super dewey but you can see from my car there was plenty of dew about by this time. 

I had run the dew heater for 8hrs on a 13,600mAh source and there was still some juice in it...the objective was clear all night though i also realise from this pic that i do extend my dew shield by quite a bit more than i thought with the camping mat (the end of my dew shield is just ahead of where that black elastic band is)...