C11 XLT - Cleaning the primary mirror and corrector plate.

[Star101]

It took me a while to work out what the issue was. I have had a few late nights but easy days as it was a weekend.  Last night, I looked up, the sky looked fairly clear but my subs looked very dim. Even at 10 minutes. subs. So, I parked the scope up. Removed the camera and filter. Everything looked OK there. Looked at the corrector plate ( that's the front end or the C11 ) Boy was it dirty! Not sure if someone had lit a smokey fire during the previous night or something. Looking further inside, I could see the primary mirror looking dull and dusty too. So, decided I would strip the scope down and clean it up the first chance I get!

The forecast for tonight was not so great. It was a busy day at work but in my way home I called at the shops and got a bag of pure cotton balls and de-ionised water. 

I have read lots and watched many videos on how to clean a SCT scope. My preferred method is to mark up and remove the corrector plate. Have the scope pointing slightly downwards so water falls out and not in   Set about with wet, soggy, cotton balls and clean the primary mirror. Dab it dry with new cotton balls and then finish off with a cool hairdryer. I washed the mirror and  dried it. Cleaned the corrector plate, both sides. Put everything back together being careful not to disturb Bobs Knobs ( Oh Er!! ) .

Tested the scope in the amazing clear skies I had for 20 minutes (edit!.. or was it that I had just cleaned the scope !! ), lol. Did a de-focus test to check collimation and WOW! I could not have gotten a better circular doughnut if I tried. A great success. And all under two hours work  ...Including a perfectly timed stop for tea  

So....whens the next clear sky forecast ?  

 

Dave

[Peter Drew]

This is a surprise to me.  I have been working with, and on, SCT's for over 40 years and have never had to clean a primary!  Outgassing of the factory applied inner paint work often deposits a cloudy film on the internal face of the corrector plate  after a considerable timescale and there have been exceptional conditions when all three optical components have dewed/frosted.     🤔 

[Star101]

I switch between full FL and Hyperstar quite a lot. I also use a hairdryer sometimes to blow out condensation. Its possible dust actually gets blown into the OTA.

The scope is 10 years old now. Its the first time I have ever cleaned the primary. I have cleaner the corrector plate once before. I have not yet touched the secondary mirror. At close inspection, it still looks good to me