Cleaning SCT Corrector Plate

American Association of Variable Star Observers (AAVSO)
Wed, 01/02/2019 - 16:16

Hello! I had to clean the corrector plate on my 8" Meade Classic because of water droplets.

    I've cleaned it had some haze in a few areas of the corrector plate where the cleaning mixture appeared to dry. I used distilled water, 91% rubbing alcohol in 1:1 mixuter and a drop of Kodak Photoflow, along with medicinal grade gauze to appy the solution to the plate.

   I cleaned it a second time, and the haze is better, but still present.


    1) Does this residual haze affect the qua;ity of photometry? Or will variables and comps be affected to the same degree such that accuracy is not affected?

    2) What methods have folks used to get pristine corrector plates after cleaning?

    3) Should I redo my system's Transforms after cleaning for water droplets?

    Thank you and best rgards




American Association of Variable Star Observers (AAVSO)
Cleaning SCT corrector

Here's the method I learned from a very experienced ATM'er and glass pusher.  This method uses 4"X4" Webril  "handy pads" which are available on line.  There are probably other products that work as well, but Webril is cheap and easily available.  

I do this when the scope (14") is horizontal, but I think any position is probably okay. 

First blow off any loose dust with an air bulb.  Put your cleaning solution in a small spray bottle.  I got mine at Target.  Spray the corrector with a very fine misting of the solution.  Don't spray so much that drops run down the surface.  

Apply the pads to the corrector.  The pads will stick to the moist surface.   Cover the corrector with Webril pads.  Then spray more solution on the pads until they look saturated, but don’t get them soaking wet to the point that the solution runs down into the seam where the cell and corrector meet.  This is not as tricky as it sounds: the  Webril is very absorbent.  Gently adjust the position of the pads so that all the glass is in contact with the pads.

Wait at least two minutes.

Gently remove the pads without wiping or putting any pressure on the corrector.  If you see a spot that needs attention you can use the corner of one of the pads to swipe gently over the spot without applying any pressure with your finger.

The idea is to keep the surface of the glass in contact with the cleaning solution long enough to allow the solution to do its work. 

I use this all my SCT’s.  I’ve seen it used on a 20” mirror and an 8” refractor lens.  I’m always impressed with the results.

Transforms:  If you just have some dust and  small spots to clean off perhaps it's not necessary to redo your transforms.  If I had, as you describe,  a haze covering the whole corrector I would probably redo the transforms after cleaning.