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Condensation Stains on My New C8 Corrector Plate

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#1 Gary Minder

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Posted 13 July 2013 - 02:13 PM

I had my new Celestron C8 out last night for an extended imaging session. I used a dew shield and there was no dew on the corrector plate when I was done, but apparently after putting the cap on and putting the scope into its shipping box in my unheated garage, condensation formed and dried. The pic below is what I found this morning.

The stain is on the side that was facing down. The plate also picked up some dust. I have read Celestron's instructions for corrector plate cleaning and will pick up what I need later today.

If anyone has any advice for how I should proceed with cleaning my new C8 I'd love to hear it. I also need to come up with a way of making sure this doesn't happen again. Should I keep the scope on the mount and point it down? Leave the cap off?

I'm afraid of this happening again and staining the mirror, or the inside of the corrector plate. I actually don't know that it hasn't already happened. I'm assuming/hoping the stain in the picture is on the outside.

What's the best practice for handling an OTA after an imaging session to minimize condensation/staining?

Thanks much.

Gary

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#2 T1R2

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Posted 13 July 2013 - 02:27 PM

Hi Gary, I'd recommend to use the "Cleaning and Modifying the C11 beast" article in the "How to" section of CN, I used that and it made me more confident I could do it and do it right. its not hard just take your time.

#3 Brian Risley

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Posted 13 July 2013 - 03:20 PM

Are you sure that is a condensation stain, almost looks like a snail path! Its really uniform in thickness and density.
Brian

#4 Gary Minder

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Posted 13 July 2013 - 04:58 PM

Are you sure that is a condensation stain, almost looks like a snail path! Its really uniform in thickness and density.
Brian


I laughed when I read that but it's actually very possible. There are no shortage of slugs around here and considering where I laid the cap when I set up, it's quite possible a little one took a ride to the garage when I put my scope away.

I tried cleaning a very small spot along an edge with the Celestron recommended iso/distilled water mix and the trail or condensation stain comes off easily.

Thanks for the tip.

#5 Brian Risley

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Posted 13 July 2013 - 06:13 PM

Having personally seen what water snails do to a primary/secondary, that was my first impression.
Brian

#6 GlennLeDrew

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Posted 14 July 2013 - 01:22 AM

To prevent future occurrences, you need to think in terms of moisture content (absolute humidity) in the air in the various environments the scope finds itself in, like indoors, garage, shed, outside, etc. And how the temperature changes will then affect relative humidity.

One good example. Taking a chilled scope indoors when the house dew point is higher than the scope's temperature results in instant condensation if the scope is not protected.

If the scope is put back in its case, but that case has air within which has a high dew point, same problem. The case should be first brought outside so that its air can be exchanged.

Furthermore, be most careful about moist air inside the scope when taken out on cooler nights. For then condensation on the inside is quite possible! Remember, it's near impossible to fully seal a scope, and diffusion will always be striving to equalize the partial pressures of the gasses of the atmospheres inside and out. Over time, moister summer conditions can lead to a higher water vapour content inside. If this is a concern, occasionally 'flush' the air with that known to be drier. This is easily done outside before observing on a cooler evening when the dew point is lower than it has been for a while. Just open up the back end for a half hour or so; this will probably not result in a complete exchange, but it's a good start. You could expedite things with some means of blowing air in. (Naturally, for SCTs employing corrective lenses inside the rear baffle, this is not possible. But if fans are installed in the rear cell, they should achieve the same thing.)

There are other aspects to be aware of, but this covers the important stuff. Always be aware of moisture content, and understand the concepts of relative and absolute humidity. (Hint: Warm air at low relative humidity can contain more water vapour than cold air at high relative humidity.)

#7 orion61

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Posted 15 July 2013 - 09:18 AM

They make condensation control dew covers with a dessicant
pouch that would help with that.
I would wipe off my dust cap before putting it back on after observing.

#8 Ed Holland

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Posted 15 July 2013 - 08:02 PM

They make condensation control dew covers with a dessicant
pouch that would help with that.
I would wipe off my dust cap before putting it back on after observing.


Very good advice this :)

I always try and keep my covers dew free (got caught out once or twice early on). At the least I'll put all the scope and finderscope covers under something, or use the objective cover itself for this, and place it so the inside faces down. Plastic bags might help too. Admittedly, dew isn't a big problem here...

Ed

#9 Reid W

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Posted 15 July 2013 - 08:07 PM

Please cue up Steve Martin, "waiter, there are snails on her plate!"






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