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Dew heaters and where to fit them


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The idea is to warm, very slightly, the objective. That's to say don't warm the dewhshield, so keep the heater around the objective.

'Running indoors' will raise eyebrows here, I suspect. I'd call it a total waste of time, to be honest!

Olly

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8 minutes ago, ollypenrice said:

The idea is to warm, very slightly, the objective. That's to say don't warm the dewhshield, so keep the heater around the objective.

'Running indoors' will raise eyebrows here, I suspect. I'd call it a total waste of time, to be honest!

Olly

I might have not explained well, I'm looking to prevent dew when using my 8" dob, my 4" heritage is used for short sessions between clouds, when grabbing for a quick hour so no point worrying about dew, from experience you don't typically run anywhere with an 8" on a dob mount, so for clarity.....

Do you fit a dew heater around top of tube, one round bottom of tube, one round eyepiece or is that overkill in uk climate? And is that the best place to fit the heaters? Any images of heaters fitted appreciated and if on a Skywatcher 200P even better

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no raise eye brows here, due to illness I do 90% of my imaging and skywatching from indoors " no offence Olly" all the best telescopes around the world do it, but I still get problems with dew, I have 3 dew heaters one for the objective, one for the finder and one for the eyepiece, I maybe need to use them between 4 and 8 times a year usally in spring and autum. hope this was helpful. charl.

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11 minutes ago, xtreemchaos said:

no raise eye brows here, due to illness I do 90% of my imaging and skywatching from indoors " no offence Olly" all the best telescopes around the world do it, but I still get problems with dew, I have 3 dew heaters one for the objective, one for the finder and one for the eyepiece, I maybe need to use them between 4 and 8 times a year usally in spring and autum. hope this was helpful. charl.

Thanks Charl, hadn't thought of finder!

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This is the position of my heating straps, the primary heater, I use it 30 minutes before I get the telescope inside the house for temperature from 0 to bellow to -15 Celcius. It's not required during observation and it it will cause tube current, but really effective to keep the mirrors warmer before I get them inside the house, preventing dew formation on the surfaces.  

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Q9aO8VZ.jpg?1

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4 minutes ago, N3ptune said:

This is the position of my heating straps, the primary heater, I use it 30 minutes before I get the telescope inside the house for temperature from 0 to bellow to -15 Celcius. It's not required during observation and it it will cause tube current, but really effective to keep the mirrors warmer before I get them inside the house, preventing dew formation on the surfaces.  

fVVFH67.jpg?1

Q9aO8VZ.jpg?1

Thanks for the images and the explanation

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Assuming we are talking about your 100mm and 200mm Dobs in your signature.

As these are Newtonian reflectors, what many find is they are much less prone to dewing up than refractor objectives and SCT/Maksutov front correctors.  If Newtonian dewing does occur, it’s usually the eyepiece and the secondary mirror that cops it.

On rare occasions, I use a 12 volt dew gun to remove dew from the secondary, fired down the focuser, having first removed the eyepiece. This will remove light dewing. If the dew is bad enough to have formed droplets, then it’s time to pack up for the night. For me, it’s only ever got that bad if I’ve gone indoors for a cuppa and neglected to cap the front end of the tube. The dewgun should sort any eyepiece dewing. I keep eyepieces not in use in the inside pockets of my top outer garment. Dewed eyepieces are a rare occurrence, unless I go in for that cuppa, leaving an unprotected eyepiece in the focuser, then it’s completely my fault.

On very damp nights, I extend the front end of the Dob tube with camping mat foam, this gives extra protection for the secondary.

Open tube Newtonians are a different matter, there are secondary heaters for those, fitted directly to the back of the secondary.

HTH, Ed.

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I have a special strap for the finder too, that one is very useful during the observation, the front lens of the finder will usually collect dew quickly and ruin my hunting experience,  These are version 1.0.. but they do the job. The eyepiece strap I don't use it much, but for the finder, I can't live without it.

( I am planning to heat the eyepiece box instead.. and that makes me think. I have to order nichrome wire.)

zpfSt5y.jpg?1

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16 minutes ago, N3ptune said:

I have a special strap for the finder too, that one is very useful during the observation, the front lens of the finder will usually collect dew quickly and ruin my hunting experience,  These are version 1.0.. but they do the job. The eyepiece strap I don't use it much, but for the finder, I can't live without it.

( I am planning to heat the eyepiece box instead.. and that makes me think. I have to order nichrome wire.)

zpfSt5y.jpg?1

Cheers, have read that dew is not so much of a problem for a reflector? But the finder is so although I hadn't considered it, it is probably the priority

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I experienced secondary dew 1 time only actually during a 80+ humidity night, never had any dew on the primary yet. When it's 89% humidity outside I don't do astronomy anymore.

I heat the mirrors at the end of my observation to be able to get the telescope inside the house after a very cold session (+5 to  -15 celcius or less.) This will prevent massive water formation on the mirrors while the gear is heating up inside the house, sealed in a bag. Mirrors are still cold with the heater, but far less then they would be without it.  It's very effective.

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I have the dew strap wrapped just behind the black lip at the front of the SCT....so its literally sitting around the position where the corrector plate it, and than I have the dew shield slipped over the SCT  and the dew strap....works like a treat, never had a issue with dew since.

 

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I have a dew strip for the main tube, I did use an astrozap heated dew shield (these are great and I recommend them) . Unless ur not goto, I would say ignore the finder, you don't use it much. I also have an eyepiece dew strip, but I find I don't need it really. My dew strap on the sct fits on the end, then I slip the dew shield over it. Hope that helps?

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On 19/11/2017 at 01:41, MarsG76 said:

I have the dew strap wrapped just behind the black lip at the front of the SCT....so its literally sitting around the position where the corrector plate it, and than I have the dew shield slipped over the SCT  and the dew strap....works like a treat, never had a issue with dew since.

 

Any chance of a photo of how you attached it and what you used. My 8SE dews up regularly here in the damp UK.

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I've always found that except on very wet nights, which to be honest are not great for observing anyway, just extending the tube with a dew shield and having a little heater tape on the back of the primary, and a short tape around the finder. 

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13 hours ago, brobat said:

Any chance of a photo of how you attached it and what you used. My 8SE dews up regularly here in the damp UK.

This is my astrozap dew strap position photos as requested.

The strap is around the orange tube just behind the lip at the front of the 8SE...

Than the dew shield is sitting on top of the lip and strap... I cut an opening to allow the dew shield to slide in a bit deeper.

Astrozap is just sitting at 50% most of the time and I rarely need to change it... if it's a dry night I just turn off the dew heater...

with this setup I never had problems with dew... ever.

 

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Hi David, never had any need for dew protection, the secondary is vulnerable but I use a dew shield to protect this (and from extraneous light).  In my opinion the primary mirror is too far back in the OTA to be affected by dew.  Always plenty of condensation when brought into the warmer house from the outside though.

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5 hours ago, rwilkey said:

Hi David, never had any need for dew protection, the secondary is vulnerable but I use a dew shield to protect this (and from extraneous light).  In my opinion the primary mirror is too far back in the OTA to be affected by dew.  Always plenty of condensation when brought into the warmer house from the outside though.

Same here, newts dont need heaters tbh (if using a dew shield). But for the frac, I just pop one heater strip where the objective is, no controller as such - I just plug it straight into the power supply.

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