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SCT, tempest fans and salt air... thoughts?

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#1 dhammy

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Posted 01 August 2020 - 06:25 PM

Trying to get some sort of consensus here or advice from anyone with experience of this. I live in Puerto Rico about a mile or so from the sea. I'll be getting a C14 for planetary imaging and I'm wondering about the use of tempest fans on a new C14 (not the edge version) when there is salt in the air. 

 

The OTA has the vents so it's not a completely closed system anyway but I've the following questions:

 

1. Would the salt in the air damage the inside of the OTA over time? The outside I can wipe off with a damp towel - doing that to the inside, not so easy. We have high humidity here on the island but there will be some nights I can image with no dew forming.

 

2. Would tempest fans blowing air into the OTA introduce anymore salt (to stay) than what would come in through the vents anyway? Meaning - what would have to happen for salt to be deposited inside, rather than just getting sucked back out again in the air. 

 

3.Would bringing the OTA down to equilibrium using a fan blowing on it from the outside be a better option given that we don't have large temperature swings during the night here? 

 

I've already had one conversation with an imager close to the sea who doesn't use them.

Thanks


Edited by dhammy, 01 August 2020 - 06:26 PM.


#2 ed100

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Posted 01 August 2020 - 06:31 PM

That's an excellent question. I'd love to know the answer myself. Have you emailed Celestron? 


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#3 dhammy

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Posted 01 August 2020 - 06:37 PM

That's an excellent question. I'd love to know the answer myself. Have you emailed Celestron? 

No, I've not emailed them yet. I'll probably do that if no-one on here knows.



#4 KTAZ

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Posted 01 August 2020 - 07:05 PM

My primary and secondary concerns would be, well, the primary and secondary mirrors.

 

Sorry, just had to do that.

 

Anyway, the filters that you select for those fans will be important. HEPA filters can capture super small particles in the size range of 0.3 to 10 microns. Aerosolized sea salt runs in that range, but the predominant size would be above the 1 micron range with very little in the sub-micron range.

 

I'd definitely have great interest in hearing what Celestron tech support says about the effect of sea salt on their mirror coatings.


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#5 Bean614

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Posted 01 August 2020 - 07:09 PM

Or, you could Insulate the OTA.  Reflectix. 


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#6 Migwan

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Posted 01 August 2020 - 07:39 PM

Interesting question.   I run two fans initially every night and leave one on low after that.  Even on humid nights.  Wouldn't leave home without them.  

 

Would drying the air via a desiccant filter remove the salt?

 

jd



#7 Cpk133

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Posted 02 August 2020 - 10:44 PM

What kind of temp drops do you have in the tropics?  I'd try the insulation route first.  Too many stories of fogging internals.



#8 dhammy

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Posted Yesterday, 03:17 PM

My temperatures drop by 2-3 degrees Celcius over the course of the night. I’m not sure if anyone has any conclusive data on how quickly a C14 typically cools and whether it would have issues with this drop.

 

My gut feeling is to use a thermocouple of remove the guesswork and determine exactly what is going on temperature wise in the scope before pumping in salt air. If I don’t need to do it, then I won’t.

 

 


Edited by dhammy, Yesterday, 03:17 PM.


#9 Astrojedi

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Posted Yesterday, 05:51 PM

Celestron OEM mesh used in the vents is 60 micron. The Tempest fans use a 55 micron mesh. Sea Salt aerosols are 0.05 to 10 micron in size (https://en.wikipedia...ea_salt_aerosol). So I think the sea air can definitely get through the mesh in either case whether or not you actually turn on the fans.

 

How damaging this is to the optics will depend on the coatings. I live in San Diego not far from the coast and have not heard of many instances of ocean air destroying optics. Now this  assumes the OTA is stored indoors when not in use. If so, I think you will be fine.


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#10 Astrojedi

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Posted Yesterday, 05:52 PM

Also use reflectix to insulate the OTA. All my EdgeHDs and regular SCTs have this. Makes a huge difference and significantly stabilizes the thermals.


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#11 chuckscap

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Posted Yesterday, 06:09 PM

Or install a .1 micron filter in front of your fans.  I did a quick search and found a few, can't vouch for them


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