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Is my C8 upside down?

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#26 ccwemyss


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Posted 08 October 2021 - 07:21 PM

Just to clarify, I don't image. But when I first got the C14, I remember being stunned by the planetary detail I was seeing (as long as it was on one side of the meridian, because the flop of the mirror would take it out of collimation on the other side). Now it just matches my 6" refractor for resolution, but brighter. 


I did experiment with tightening the retaining ring to reduce the flop, but it took a level of pressure that pinched the optics (very visible in a star test). I also tried flop stoppers, but if I snugged up the focuser to take out the flop, the mirror was angled over noticeably. That's when I concluded that it was a loose primary.


Celestron made me go through a whole series of tests before they were convinced of my diagnosis, and finally issued an RMA. Once it got there, they lost track of the repair ticket, and sent me a notice that it was cleaned, collimated, and being returned. It took quite a bit of effort to get a real person on the phone who could have them call the package back from FedEx to do the requested repair. After gluing it, they spun the optics, collimated, and shipped it, but with the mirror locks and the rear cell screws loose. Fortunately, nothing got loose inside the OTA. 


I do see the Glatter collimators come up occasionally, but they're spendy, especially for a one-time use. I'm assuming that Celestron got the assembly aligned, and just didn't tighten the screws enough to hold through shipping. So the main thing I need to do is get the tube aligned with the baffle. But, given everything else that happened, who knows. 


Chip W. 

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#27 markb


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Posted 08 October 2021 - 09:28 PM

Sadly inexcusable treatment for their premier product. C14s. should be walked through by hand in my opinion.


The complaint they misplaced a returned OTA ticket, or did a simple CLA without repair, is one I've read too many times here, although they seem to do it right eventually.


If your optics delivered that performance when new, they will again. If they changed no optical surfaces, that only leaves alignment and, afterwards, collimation 


Were the loose screws the ones on the outside of the cell into the tube? It sounded internal in an earlier post and I have not seen an internal layout of the C14. Loose cell to tube securing screws sounds very logical based on smaller OTAs.


If they are the outer screws, any shift in rear cell angle will shift the baffle and primary axis angle.


Than might explain the direction to invert the tube to take up the screw hole slack when tightening.


But things can shift a bit when tightened, a major source of aggravation squaring three screw refractor focusers and even collimating my slip in and slip over 5 and 6" Jaeger refractor cells, also three screw secured. Set, test, reset, test, repeat, repeat, repeat. A pain. But the results are worth it.


In optics those tiny shifts jump out at you when testing. 


Also there is no way to determine the original cell position when they aligned it, and that position was the foundation for the alignment they did. I would assume C14s get the effort required to center the baffle in the tube.


The paper target method should give at least as good, and likely better results than I got. The holographic projections are fat enough to put judgment into the mix.


So I would not buy one just for this.


When I look at my holographic projection efforts, they really don't differ in intent or effect from the simple paper circles with an accurate center dot.


I never wanted to pay the Glatter prices either for infrequent use, so I watched classifieds for a long while.


I would certainly try the paper circle/ wide painters tape method. The painters tape was a CN post suggestion and it solves the securing and no residue problems. It could also form a substrate/holder for a more conventional paper centering circle. There are ways to place a center dot accurately.


If the rear cell was loose, the Wilmslow baffle runout reduction method might be a good place to start. No tools needed IIRC. But...


If shifting the rear cell to be parallel to the front cell, and the front cell to then be orthagonal to the baffle is the goal, perhaps placing the OTA face down on a regular mirror might allow use of a conventional laser with a 45 diagonal or ground glass visible return target face. 


That should provide a really simple and safe way to test and if necessary,  adjust the placement of that heavy rear cell?


If the front and rear cells are parallel the beam should return to the center of the laser face. I assume accuracy would match the target method.


If you try a horizontal OTA method, I have used a wood or plastic carpenters miter box as a stable OTA horizontal rest, and they can be screwed to a table for stability.


A big sharp C11 or C14 is a relevation to use. Worth getting it back in shape.


My apologies to the OP Potamus for the thread shift, but I think the info and discussion may help with the OPs alignment issue, still hoped to just be a 180 spun corrector / secondary.

Edited by markb, 08 October 2021 - 09:33 PM.

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