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Equipment Discussions >> Eyepieces

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csrlice12
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Reged: 05/22/12

Loc: Denver, CO
Re: Are Televue EPs water proof? new [Re: saptharishi]
      #5688882 - 02/19/13 01:02 PM

I donno, a fishing pole and a telescope, sounds like two hobbies I could combine pretty easily, gotta have something to do waiting for the sun to go down......

"Give a man a fish, and he will eat today; teach a man to fish, and he'll spend the whole summer in a boat drinking beer......"

Edited by csrlice12 (02/19/13 01:05 PM)


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Are Televue EPs water proof? new [Re: csrlice12]
      #5689109 - 02/19/13 03:35 PM

With semi-permeable seals, Nitrogen-filled will stay Nitrogen-filled a lot longer than Argon-filled will stay Argon-filled. The partial pressure of gases inside and outside the chamber will assure a faster leak rate with Argon.
But even seals that do not keep out a mixing of gases over time may keep out water vapor, and that is the salient reason for the seals in the first place.


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bremms
Carpal Tunnel
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Reged: 08/31/12

Loc: SC
Re: Are Televue EPs water proof? new [Re: Starman1]
      #5689237 - 02/19/13 04:36 PM

You are correct Don. That is a very good explanation. Best thing is using a desiccant canister in the EP box. keeps them in a dry atmosphere.

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turtle86
Pooh-Bah Everywhere Else
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Reged: 10/09/06

Re: Are Televue EPs water proof? new [Re: bremms]
      #5689267 - 02/19/13 04:53 PM

Quote:

You are correct Don. That is a very good explanation. Best thing is using a desiccant canister in the EP box. keeps them in a dry atmosphere.




That's what I do. Plus, I use only one eyepiece at a time and put on a dew heater strap the moment I see any fogging. The eyepieces I'm not using stay in the eyepiece case in the back of my Honda Element. It's usually pretty humid here in Florida, but I've never had any problems with my Televue eyepieces. I do think the waterproofing done by ES is a nice feature and sure wouldn't mind seeing Televue (or anyone else for that matter) follow suit. But in actual practice, the lack of waterproofing isn't that big a deal IMHO for astronomical use and not a factor that by itself would influence my purchasing decisions.


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BillP
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Reged: 11/26/06

Loc: Vienna, VA
Re: Are Televue EPs water proof? new [Re: Starman1]
      #5689351 - 02/19/13 05:35 PM

Quote:

With semi-permeable seals, Nitrogen-filled will stay Nitrogen-filled a lot longer than Argon-filled will stay Argon-filled.




According to this response from Argonne National labratory scientist, molecule size is about the same between the two and neither has propensity to leak more than the other.

Link

Given how simple the construction of an eyepiece is, with no internal moving parts to the optics, I am not seeing why one would expect the seals to deteriorate to the point that they would leak out? Anyone have any actual research tests that confirm that simple constructed devices can't maintain a nitrogen fill for many many years/decades?

Edited by BillP (02/19/13 05:38 PM)


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Are Televue EPs water proof? new [Re: BillP]
      #5689456 - 02/19/13 06:37 PM

It isn't molecule size, Bill, it's the difference in partial pressure on one side versus the other.

With Nitrogen, the gas is 100% on one side, 78% on the other.
With Argon, the gas is 100% on one side and 0.934% on the other.
With equal sized molecules, Argon will leak faster due to that factor.

Seals can be quite elaborate, but are usually made from rubber or a polymer of some sort. And the seals can last for many years.

But the leak around the seals is inevitable. Slow, as long as one side is not pressurized higher than the other, but inevitable.

Not a bad idea, though we've had several hundred years of eyepieces so far and most have not been sealed.


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Are Televue EPs water proof? new [Re: Starman1]
      #5689889 - 02/19/13 10:39 PM

Quote:


But the leak around the seals is inevitable. Slow, as long as one side is not pressurized higher than the other, but inevitable.




I think it is diffusion through the seal. Bicycle tubes are an extreme example. High pressure differential, large surface area, relatively small enclosed volume... a 700c-23 pumped to 120psi might be down to 100-110 psi in a week.

Jon


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Are Televue EPs water proof? new [Re: Jon Isaacs]
      #5690002 - 02/20/13 12:03 AM

Quote:

Quote:


But the leak around the seals is inevitable. Slow, as long as one side is not pressurized higher than the other, but inevitable.




I think it is diffusion through the seal. Bicycle tubes are an extreme example. High pressure differential, large surface area, relatively small enclosed volume... a 700c-23 pumped to 120psi might be down to 100-110 psi in a week.

Jon




??
Don't know what kind of tubes you use, but 120psi bicycle tires are down to 75-90psi in 24 hours. < 50psi in a week. I'm not riding several hours a day now as I was when I was racing, but when I did train hours per day, we used to air up the tires again after 12 hours because they had gotten soft.

In an eyepiece, though, the pressure is the same on both sides of the seal, so diffusion should be very very slow.


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Are Televue EPs water proof? new [Re: Starman1]
      #5690293 - 02/20/13 07:37 AM

Quote:

??
Don't know what kind of tubes you use, but 120psi bicycle tires are down to 75-90psi in 24 hours. < 50psi in a week. I'm not riding several hours a day now as I was when I was racing, but when I did train hours per day, we used to air up the tires again after 12 hours because they had gotten soft.





Don:

I suspect you were either using sew-ups or lightweight latex tubes. I never used Latex tubes but do have some disk and track wheels with tubular tires and they loose pressure quickly.

I commuted on a daily basis for more than 20 years using standard butyl tubes. Most of the bikes were setup with 23's but I also rode 20's sometimes and 25's, I pumped my tires at least once a week and they were never under 100psi unless there was a leak. At 220lbs riding a 700C x 23, any 23mm tire down to under 80lbs was a guaranteed snake bite.

Jon


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