10" dob and dew/frost.

[Kirscovitch]

I know there are a lot of variables around this question but how long could I expect a viewing session to last before dew and frost would most likely send me packing? 

I've been reading that because the OTA acts as a dew shield in itself (maybe I read that wrong) that my sessions could be extended of those with a frac but just been wondering on an average how long I can expect to go dew free?

Any tips or advice from the fellow dobbers would be appreciated!

[swamp thing]

Hi Matt

There's a few factors involved here. The site one observes from, the humidity of the air, the scope itself.

My 10" Dob has dewed up (secondary only mind you) once in all the time I've owned it (reckon its 5 years). That night was the wettest (dew wise)I remember, normally I can pretty much bottle the water running off my scope without worries. I don't even use a dew shield on my 10".

For some reason mine just doesn't dew up. It could be the tube is cardboard, or it's well oversized (diameter wise) I really don't know. Mine is home made Dob though not a commercial one.

I just observe how ever long I want.

[Naemeth]

Perhaps get a dew heater? I haven't encountered dew problems on my 10" yet though (without either a dew shield or heater)

[Kirscovitch]

Thanks for the quick responses guys. 

Hi Matt
There's a few factors involved here. The site one observes from, the humidity of the air, the scope itself.
My 10" Dob has dewed up (secondary only mind you) once in all the time I've owned it (reckon its 5 years). That night was the wettest (dew wise)I remember, normally I can pretty much bottle the water running off my scope without worries. I don't even use a dew shield on my 10".
For some reason mine just doesn't dew up. It could be the tube is cardboard, or it's well oversized (diameter wise) I really don't know. Mine is home made Dob though not a commercial one.
I just observe how ever long I want.

Those were the variables I mentioned. During the summer we get some very humid nights. 90% is not uncommon. And I guess I would be more concerned with the secondary more so than the primary. And good tips on this site have claimed a hair dryer is a good fix 

Perhaps get a dew heater? I haven't encountered dew problems on my 10" yet though (without either a dew shield or heater)

Dew heaters/shields are an option. I would lean toward the shield part though. Especially on shielding the EP's and finders. Keeping them covered when not in use and so on. 

And I guess the only thing that will really let me know what I need to do is experience. I hate to say it but after having the dob for almost 3 weeks I still haven't had it out for first light yet even though I have taken my 130 out about 4 or 5 times. Due to the extreme temps here the smaller more portable scope made more sense.

What got me thinking is a day off of work on the 14th and so far clear skies forecast. I'd be able to get the dob out earlier for the cooldown and then get a decent first light report.

[scarp15]

In-between use, point the scope downwards a little, also helpful if you can pick up on the occasional light breeze, but yep, as you pointed out, you seem to be having one hell of a winter across there.  

[glappkaeft]

Dew heaters/shields are an option. I would lean toward the shield part though. Especially on shielding the EP's and finders. Keeping them covered when not in use and so on.

A shield will be sufficient for the telescope. I'm 7 years dew free with just a shield. Since the finder is used sekdome keeping it covered is usually sufficient but I like heaters for the eye piece. If you don't have electricity you can fasten a chemical hand warmer with a rubber band. They are usually good for more than 6 hours.

[Kirscovitch]

A shield will be sufficient for the telescope. I'm 7 years dew free with just a shield. Since the finder is used sekdome keeping it covered is usually sufficient but I like heaters for the eye piece. If you don't have electricity you can fasten a chemical hand warmer with a rubber band. They are usually good for more than 6 hours.

Like the idea with the hand warmers. I have lots of them around. Would they help keeping the secondary mirror clear as well?

[Bart]

I have a 10" and don't use a dew shield for the tube. The RACI finder has a dew shield on it alright and my Telrad has been fitted with a heater http://stargazerslounge.com/index.php?/topic/203117-Telrad-Heater---Here-goes%21%21

I tried a dew shild for the tube but hated the extra length swinging off the end. It caught the breeze amongst other annoyances. I usually get 3-4 hours before the secondary goes, but I've had longer and shorter sessions. I have a hairdryer on a lead coming from the garage and a few mins giving the secondary a blast will give me another hour or two. If the conditions exist, it is a bit of a battle, but not too bad if you can get power to a hairdryer. Or even a 12v dryer and a power source if you're not near the mains.

Good luck.

Barry

[andyman]

Not had any dewng problems with mine...touch wood..but the telrad is a dew magnet even with a shield its a right pain.Its frustrating because the scopes clear of dew but the telrads not so you cant find objects

Bart cheers for the link going to try putting heater on telrad fed up of using hairdryer

[Kirscovitch]

I have a 10" and don't use a dew shield for the tube. The RACI finder has a dew shield on it alright and my Telrad has been fitted with a heater http://stargazerslounge.com/index.php?/topic/203117-Telrad-Heater---Here-goes%21%21

I tried a dew shild for the tube but hated the extra length swinging off the end. It caught the breeze amongst other annoyances. I usually get 3-4 hours before the secondary goes, but I've had longer and shorter sessions. I have a hairdryer on a lead coming from the garage and a few mins giving the secondary a blast will give me another hour or two. If the conditions exist, it is a bit of a battle, but not too bad if you can get power to a hairdryer. Or even a 12v dryer and a power source if you're not near the mains.

Good luck.

Barry

Interesting dew heater for the telrad but no way I would even attempt that. All thumbs when it comes to DIY skills.

Hair dryer will probably be my go to when at home in the yard but not sure when I'm out at a dark site. I do have a power tank that I run my SLT off of and I suppose I could find a 12v dryer.

If I wanted to craft a dew shield to put on the end, about how long should it be?