Cleaning an SCT mirror

1148 views
2 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    June, 2002
Cleaning an SCT mirror
Posted by slick750 on Saturday, July 19, 2008 9:01 AM

At what point does it become worthwhile to clean an SCT mirror? During the day it is not noticeable, but at night when you shine a light at the mirror, you can see a big smudge about the size of a palm print on the mirror(12" SCT).There also seems to be an overall haze to about half the mirror which I at first thought was dew on the primary because of the way it looked. After seeing it before observing  sessions each time I use itI conlcude that it is either something on the mirror or the coating itself. At what point does this degrade the image and make it worthwhile to remove the corrector plate and attempt to clean it. I am leary of doing this mostly because I dont want to cause any damage to the mirror coating by messing around with any cleaning products, not even mild soap and water. And I don't know how delicate UHTC coatings are either.

I would prefer not touching it at all, but it is bothering me and I am not sure how to proceed at this point....to clean or not to clean...that is the question......

Mike S.

12"LX200GPS, 6" Astrotech Imaging Newtonian, 6" Schmidt Newtonian, 4.7"Astroview, Denkmeier Binoviewer,Modified Canon350D,DSI II monochrome imager(used for guiding), handbuilt observing chair, 12x50 binoculars, 8" homemade dob circa. 1982, and way too many ep's and accessories.

  • Member since
    February, 2007
Posted by johnm on Saturday, July 19, 2008 9:24 AM

 You would probably be advised to leave well enough alone, especially the mirrors in an SCT unless you know exactly how to take apart and put one of those rather complicated instruments together again.

No mirror more than 2 minutes out of a coating chamber can show anything less than a mess when a flashlight is shined in it. 

Equipment: Some telescopes 

WRSO

  • Member since
    June, 2002
Posted by slick750 on Saturday, July 19, 2008 11:29 AM

I expect pinholes and the like, and of course you are never supposed to judge the coatings on a mirror by shining  a light from the back side but I don't think a palm sized smudge is a good idea to have on your mirror, but I suspect you are correct about not touching the mirror. I am not really as concerned with taking it apart as I am with damaging the mirror  by attempting to clean it.

The funny thing is, I sent it into Meade to have some work done on it about 2 yrs ago, and ever since it came back I haven't been convinced that the images have been good. Planetary views have not been very sharp and stars have not been pinpoints.  I wondered if it was the collimation of the scope or my binoviewers or my diagonal. I tried eliminating things so I changed to a new 2" dielectric diagonal, and stopped using my denkmeiers hoping to eliminate all other possibilities besides the scope. One night a couple months ago while I was making sure the dew was off the corrector plate I happened to notice  the above mentioned prob. with the mirror, and I thought Eureka!! I've found the problem....I just don't want to mess with it. But I was convinced that all my troubles would be solved if I cleaned the mirror. But then........bum bum bum...(qeue the dramatic music).....

About 2 wks ago while I was out observing  and getting what I felt was some great deep sky viewing with a pair of the new  27mm Meade Series5000 plossls, I took a shot at Jupiter expecting the usual  ho-hum view, but when I focused in , the planet was SHARP and the clouds had so much detail I was shocked. I had been using one of my new ep's in each of my scopes(which I originally bought as a pair for my denkmeiers because  they gave a nice low mag and the field stop was the right size for my binos)  I immediately got my binoviewers out, put both of those eps in and was blown away by the details in the clouds of Jupiter. I saw stuff I never saw before.....and the Great Off Color Spot jumped right out at me ..it was amazing.... and this was around only about 120x!!

So, I guess I have come to the conclusion that I have lousy atmospheric conditions where I live and the issue with the mirror may not be as bad as I first thought. It really surprised me though when I saw how sharp Jupiter was after all this time thinking I had a prob with my equipment....good news in the end (yay!!)

 Having said all that(whew!!), the mirror issue still bothers me but I am leaning toward your way of thinking john(thanx for your input). I just thought I would see what the general concensus on here was.

 

Mike S.

 

12"LX200GPS, 6" Astrotech Imaging Newtonian, 6" Schmidt Newtonian, 4.7"Astroview, Denkmeier Binoviewer,Modified Canon350D,DSI II monochrome imager(used for guiding), handbuilt observing chair, 12x50 binoculars, 8" homemade dob circa. 1982, and way too many ep's and accessories.

Join our Community!

Our community is FREE to join. To participate you must either login or register for an account.

ADVERTISEMENT

FREE EMAIL NEWSLETTER

Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter.

ADVERTISEMENT
ADVERTISEMENT
Find us on Facebook

Loading...