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Alan White

Dew Control on a Dob or not?

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A question out of curiosity of present.

On say a 200p Dob, do you need to control dew?
I got away with it on my 150p Newt but on a longer tube Dob is it the same, no dew heaters or what do you do?

 

Thinking of the future at present and have too much thinking time on my hands....

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Almost never had dew problems with my 13,1" Odyssey (solid tube); rarely (once or twice a year, and only on the secondary after observing more than three hours) with the 18" and the 8" truss tube dobs, which are both fitted with light shrouds. No dew heaters installed; a fan, or (with the 18" and it's Sitall secondary) a small heat pack in a bag hung under the secondary cage for a few minutes are always enough.

Stephan

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i use a kendrick heater on my secondary, but i don't always turn it on. only time i do is when you know everything around you is cooling and dew forms.

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53 minutes ago, Daniel-K said:

yes........

Thanks Daniel-K , but that's half an answer.
What do you do to control it?

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yep, in my garden we have a lot of shrubs n trees, so dew is a problem, I use two straps, hi tec astro ones and a 4 point controller, I put a large one round the body at the mirror, and one on the eyepiece, that keeps it off the secondary as well, and a homemade snood

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4 minutes ago, Alan White said:

Thanks Daniel-K , but that's half an answer.
What do you do to control it?

same as me alan, secondary heater and ep heater, we all do the same with our dobs to be honest

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Seldom a problem, eyepieces, filters and telrad can each suffer from the effects of dew, telrad is an easy fix with a wipe from a camera lens / spectacle cloth. My 8" and 14" solid tube dobs each have fan systems for the primary, which I rarely ever use. Some precautions can be applied, such as never leave the scope pointing up, skywards in-between observing periods. I have also flocked my scopes (at least primary and secondary regions) and this material perhaps helps a little towards absorbing moisture.  

If my scope{s) do succumb to the effects of dew, that is that I am observing in an area highly prone to this, then I will take along a 12V hairdryer and give the secondary a blast with this, though I haven't used or felt the need to for ages.

Edited by scarp15
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I use a homemade dew shield, not so much to protect the mirror on my Skyliner, which sits at the bottom end of a solid tube, therefore pretty much protected, but I use the dew shield more so to extend the length of the OTA in order to cut down some of the stray light from bouncing around the OTA. Im not sure this one works 100% because the material is made of blue camping underlay and to be honest has some reflectivity about its surface.

If dew becomes a real  issue and the exterior of the OTA wets out, I just put the scope back indoors, there's always another night.

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1 hour ago, faulksy said:

we all do the same with our dobs to be honest

Sure do buddy thanks to your top anti dew kits. :thumbright:

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I would recommend having it, but it's not always necessary to use it.

A heater on the secondary creates little heat currents in the air so I try to minimise using heat on the secondary.

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55 minutes ago, swamp thing said:

Sure do buddy thanks to your top anti dew kits. :thumbright:

just thought, i made everyones :icon_biggrin:

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I've never found dewing an issue with the solid tube newts / dobs that I've owned which include the 8" and 10" Skywatchers and my current 12" F/5.3 Orion Optics. I do use a light shield at the top end of the tube to keep stray light off the secondary mirror / focuser though (I have some issues with lights around my observing site).

The tendancy for dew may be linked to location though. My garden (my usual observing site) is 300 feet up. If your observing site is lower, close to a river or lake things might be different ?

 

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I never suffer from dew on my secondary in my 250px solid tube, but absolutely need my 'Dew Guard' heater on my 15"!

Edited by niallk
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10 hours ago, faulksy said:

just thought, i made everyones :icon_biggrin:

Well, allow @Mrs Racey and me to extend our appreciation if we too are now the beneficiaries of your craftsmanship :thumbsup:

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9 hours ago, John said:

The tendancy for dew may be linked to location though. My garden (my usual observing site) is 300 feet up. If your observing site is lower, close to a river or lake things might be different ?

I'm sure this is correct John. I'm at about 30ft, between two large London reservoirs and not so far from the Thames and River Mole. Dew is definitely a problem around here.

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I have had dew settle on the primary on my 10" Orion USA solid tube dob a few times now. However this has happened when I am camped out in a field at a star party. 

So location likely plays a part in this. Next time I will try peg out a ground sheet to see if that helps. Once I remember being dewed out and I thought having drove 90 miles to be at a dark site I was not going to let a bit of Earth bound moisture spoil the night! So I resorted to `gently` ( very gently) warming the primary with a camping stove stood under the back of the scope for 15 minutes! It worked but I can`t endorse this practise, so the usual warning is, don`t try this at home kids!

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8 minutes ago, Phil Fargaze said:

So I resorted to `gently` ( very gently) warming the primary with a camping stove stood under the back of the scope for 15 minutes! It worked but I can`t endorse this practise, so the usual warning is, don`t try this at home kids!

Eeeeek! Brave stuff! I often resort to a hair dryer but that's often not practical out in the field just using a battery. Prevention is better than having to clear dew.

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9 hours ago, John said:

 

 My garden (my usual observing site) is 300 feet up. If your observing site is lower, close to a river or lake things might be different ?

 

300ft is a good height, we are 1100 above sea level, most of the time we are in the cloud, but sometimes we are above it, makes a pretty sight lookng out on a cloud bank in the Shibden valley

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11 hours ago, faulksy said:

just thought, i made everyones :icon_biggrin:

Ahem everyones :icon_scratch:

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51 minutes ago, Phil Fargaze said:

So I resorted to `gently` ( very gently) warming the primary with a camping stove stood under the back of the scope for 15 minutes! It worked but I can`t endorse this practise, so the usual warning is, don`t try this at home kids!

Please heed Phil's own warnings here folks.

This is extremely dodgy and the smallest mistake will mean it's "New mirror please" 

You have been warned.

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31 minutes ago, nightfisher said:

300ft is a good height, we are 1100 above sea level, most of the time we are in the cloud, but sometimes we are above it, makes a pretty sight lookng out on a cloud bank in the Shibden valley

And folks down in the valley forlornly  open their curtains to a dull day, whilst those up above are smiling  in the sunshine - makes for change.

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1 hour ago, Stu said:

Thames and River Mole

One of my old favourite fishing haunts as a teenager, just under the railway bridge, Hampton court, where the Mole Joins the Thames.
How time passes so quickly!

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Seeking out higher open ground for observing definitely has distinct advantages and some disadvantages. One of my favourite observing sites is at 286m / 938.32 feet above sea level. Sometimes a mist can be seen to form lower in the valley and being fairly open, the night breezes will help prevent condensation build up and in late summer, when I plan to return, help keep mozies out of the air. Across moorland, at this elevation can also be good for picking up lower lying targets. However a breeze in the valley can blow a hoolie higher up, I often to have to don my down jacket or vest regardless of the time of year.  The light dome in the South East from Tyneside is a bit more prevalent.  Even so dew can still become a nuisance at times, just less often than lower down and close to water sources. Another preventative, is when taking a coffee break and to check charts, I may put back on the breathable Astrozap dust cover on the secondary end, the primary cover remains on throughout.  I also place the scope on a rubber ground mat, which is situated on short grass on the verge of a small gravel parking space.

Edited by scarp15
word change
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