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Internal dew buildup or something else on my SCT?

Celestron Classic Optics SCT
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#1 robbistron

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Posted 08 December 2023 - 03:06 PM

I recently acquired a used Celestron C5 and the views are pretty sharp (though I've gotten a chance to observe from it only twice). Even at 50x magnification, the moon's edges were detailed, could see Saturn's rings, Jupiter's surface and its moons. While aligning the finderscope this afternoon, I couldn't help but notice some "marks" on the inside of corrector plate that seemed like patches of condensation. The scope was outdoors for about 20 minutes, pointed West towards horizon, the sun was close to Zenith. 

 

Location: South Florida, USA

Temperature: 77F (25C)

Dew point: 62F (17C)

Precipitation: 0"

Humidity: 61%

Time: 2:30pm

 

Is this internal dew buildup? Is it normal? Can it be prevented? Or is it something else? Does it need cleaning? Should I even be concerned?

 

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#2 firemachine69

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Posted 08 December 2023 - 03:34 PM

Mold spores starting.


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#3 robbistron

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Posted 08 December 2023 - 03:51 PM

Mold spores starting.

That's a great direction, plenty of discussions on this topic. Seems like it requires the corrector plate to be removed and mold be cleaned?



#4 maroubra_boy

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Posted 08 December 2023 - 03:52 PM

Mould, as firemachine69 said.  Symptom of poor storage conditions and a scope that was not allowed to dry off properly before packing it away.


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#5 robbistron

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Posted 08 December 2023 - 04:08 PM

Thank you for identifying the issue here. I went through a few forums about the mold issue and watched videos on how to dismantle the corrector plate for cleaning. It seems like all that needs to be done is to remove the screws on circumference and pull the plate out. However, my C5's screws are already missing (marked in yellow) and there is white residue (adhesive?) that's probably holding the plate in position (marked in red). Should I pull the white adhesive out to remove the corrector plate or did the older C5s have a different way of removing the corrector?

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#6 Dynan

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Posted 08 December 2023 - 04:08 PM

Clearly mark the positions of the corrector plate and the secondary mirror BEFORE you take it apart of any cleaning that you may do.


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#7 firemachine69

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Posted 08 December 2023 - 04:22 PM

Clearly mark the positions of the corrector plate and the secondary mirror BEFORE you take it apart of any cleaning that you may do.

 

 

 

I second this and CAN'T STRESS THIS ENOUGH. lol.gif waytogo.gif


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#8 jeffreym

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Posted 08 December 2023 - 04:27 PM

Thank you for identifying the issue here. I went through a few forums about the mold issue and watched videos on how to dismantle the corrector plate for cleaning. It seems like all that needs to be done is to remove the screws on circumference and pull the plate out. However, my C5's screws are already missing (marked in yellow) and there is white residue (adhesive?) that's probably holding the plate in position (marked in red). Should I pull the white adhesive out to remove the corrector plate or did the older C5s have a different way of removing the corrector?

attachicon.gif disassembly.jpg

The old white C5s utilized a threaded retaining ring.  I think your yellow holes are for a spanner wrench not for screws.  That entire ring should spin to thread out.  To repeat, mark the position of the secondary.  Don't let the secondary spin when you first start unscrewing the retaining ring.  Once the ring is out, use a couple pieces of scotch tape from the tube to the glass at about 30 degrees apart.  Cut the tape with a sharp knife then you can remove the secondary and be able to put it back.  Scotch tape will not leave anything behind when you take it off.

 

Have fun!

Jeff


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#9 robbistron

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Posted 08 December 2023 - 05:10 PM

Jeff, you’re awesome! With the information I was able to find this old thread. https://www.cloudyni...or-plate-on-c5/
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#10 jeffreym

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Posted 08 December 2023 - 05:42 PM

Jeff, you’re awesome! With the information I was able to find this old thread. https://www.cloudyni...or-plate-on-c5/

Thank you.  That is a good thread; I'm am glad you were able to track it down. 

 

The "glue" is probable there to keep the ring from coming loose.  There was a lot of space around the outside of the corrector in mine, so, I installed three 1/2" lengths of cork that were the same thickness as the excess space to center the corrector in the housing once reinstalled.  That way the position of the glass was not dependent on the tightness of the retaining ring.

 

Jeff



#11 robbistron

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Posted 10 December 2023 - 12:16 AM

Update: The mold has been cleaned. These are the steps I followed:

 

1. Marked the position of corrector plate using scotch tape.

2. Inserted two pins in the retaining ring and unscrewed it. Corrector plate came out nice and easy.

3. Cleaned the moldy side with soap solution, followed by rinsing with hydrogen peroxide. 

4. Gently rubbed cotton pads over the corrector, going from center to circumference.

5. Rinsed with water, cleaned again with soap solution and dried with cotton pads (again going from center to circumference).

6. Blew a hair dryer (for about 5 seconds) over the corrector to ensure everything is dry.

7. Placed the plate back to the scope tube, aligning the position marks (scotch tape), the corrector dia was about 3mm (~1/8") smaller than the tube body so I placed the corrector as close to center as possible.

8. Screwed the retaining ring back and collimated.

 

Voila! Back to sharp views and no mold (as of now). Would keep an eye out for new growth.

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#12 Old Speckled Hen

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Posted 10 December 2023 - 02:08 PM

That's a great direction, plenty of discussions on this topic. Seems like it requires the corrector plate to be removed and mold be cleaned?

Now do it again properly.

 

You've missed the carp on the outside edge of the plate.


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#13 firemachine69

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Posted 10 December 2023 - 07:49 PM

Now do it again properly.

You've missed the carp on the outside edge of the plate.


Outside the FOV.

#14 Old Speckled Hen

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Posted 15 December 2023 - 02:06 PM

Outside the FOV.

still looks carp.




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