[ngcles]

Hi Stefan,

I was gifted a used 20cm Celestron CPC several months ago. After I brought it home I discovered a very ugly/nasty-looking stain on the inside of the corrector plate (see attached photo). The previous owner had drilled a small hole in the corrector plate mounting cell to attach something and a fluid had made its way inside the tube at some stage and dribbled down the back surface of the corrector. It looked as though the coating was flaking and or corroded.

I had never attempted to clean a STC corrector before (I'd never owned an SCT) and was naturally very apprehensive so I approached Don at Bintel for his expert advice -- and sent him a photo. He felt that it was probably only a water stain and would be very surprised if the coatings had been damaged. He advised to clean it inside and out with a wad of clean cotton waste and Windex. He said the coatings were very hard and durable and that Windex was just fine for the job.

I found there are many youtube videos demonstrating how to disassemble the corrector plate and it took less than ten minutes to remove after I created a couple of registration marks so that, upon re-installation, it would be back in precisely the same spot.

It took just a couple of wipes to remove the offending stain and after a thorough cleaning that took about five minutes it was re-installed -- squeaky clean like a brand-new one.

Star testing that night revealed collimation was still A1.

Don't know about whether that cleaning advice could be applied to corrector plates and or coatings made by other manufacturers, but it worked a treat with the starbrite coatings on the Celestron.

Best,

Les D