Cleaning Optics of Celestron Edge HD 8-inch SCT

First of all, I am happy that you discovered the fact that such defined defects (motes) were from dirt on the sensor window and not on the OTA optical surfaces.  Also that dirt on the corrector, or objective cannot yield such defined defects, rather just reduce the light throughput.  Although, note below for my experience.  Most dust or haze on the optics only really affects light throughput, but regular structured "dirt" such as a spider web or other regular stuff, can cause unwanted diffraction spikes, etc.  Also, a slight increases in diffused light background.  But this latter issue seems to be of no concerns with professional scopes, so why should we care.  But that would be for very dirty optics.

I had an interesting problem about 18 months ago that motivated me to open the front of my RASA 11 OTA.  I had baby spiders invade the interior of my OTA.  Too small to notice these guys even when cleaning out the OTA, but the ultra thin webs that criss crossed the interior caused a significant degradation via wild diffraction spikes around bright stars and objects.  These are so thin that they are literally invisible under all circumstances, except when viewing down the OTA through the corrector at night with an LED headlamp.  In any case, I was not about to send the scope back to Celestron for the 3rd time that year for another cleaning.  (The first time was to correct a manufacturing defect, the second was because during the repair, they cleaned the optics and returned it with a big fat thumb print on the objective.  Totally unacceptable!)

From what is written, RASA's correctors are particularly fussy about positioning, not just centering, or rotationally, but also tilt.  This is clear when I looked at my corrector plate cell with all the random positioning of the cardboard shims used to tune this baby.  So I was not about to remove the corrector from its cell!  Just marking the corrector's rotational position would not be a perfect solution.

*In my opinion, I think Celestron does its customers a disservice by not making these telescopes more easily servicable.  Shipping these scopes back to Celestron for service and cleaning is not only a pain, and expensive to do properly(the shipping, that is), but comes with its own risks.  And the need to do so for customers overseas probably scares potential customers overseas from going in this direction.*

I believe the solution is a simple design change that allows the removal of the corrector cell intact with the corrector plate.  All that would be required is to use captive nuts on the inside of the OTA that hold the cell in place.  I know this because that is what I did.  I figured out a way to remove the screws and the whole cell slides off the OTA tube easily.  It is very easy to clean the corrector (meaing the inside surface) while it remains snugly within its cell.  It is much easier to handle the corrector when it is mounted in its cell and likely safer.  And when returning the cell and corrector to the OT, it is automatically repositions by the location of the screws.  The screw holes are small and tight to the screws, so there is essentially no rotational or translational (front/back) play.  I can confirm that the performance once I removed the corrector cell, cleaned the webs, and inside of the plate (I also blew the little bit of dust off the objective and vacuumed out the dust) was the same as prior to the cleaning. 

When I removed the screws during the start of the process, the nuts fell on the inside of the OT.  They were accessible after removing the cell.  To facilitate doing this in the future, I glued these nuts in position, to make them captive.  The screws were then waxed, so they wouldn't get stuck by the glue.  First, I cannot advise people to try this with their scopes.  One reason is that all it would take is to have removed all the screws but not having that last screw come out!  How often have we experienced that on other projects?!  In such a case, you would not be able to take the cell off and get to the loose nuts inside the OTA.  Then you would have to remove the corrector plate anyway!  But it would be a piece of cake for Celestron to use captive nuts or braised on nut plates to facilitate removal of the assembly.  That would allow the customer to do basic servicing inside the OTA and preserve the technical servicing of the optics by Celestron or licensed service partners.  From my experience, Celestron technicians seem to not be interested in doing simple cleaning service on scopes and that seems to show in the quality with which they did that service on my scope.  So why not give the customers the ability to do it themselves?