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  1. C14EdgeHD
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Centering C14

 

So I have a C14 Edge.? I am having I think a centration issue.? I am using a Feathertouch focuser on the back end, screws onto the rear cell.? Collimation is after the scope has acclimated for several hours, Do not use a diagonal, straight through the back end.? Star at fairly high elevation.? Start at low power and work up.? The corrector was centered by the folks who sold it to me.? Using the primary mirror locks.? I am somewhat outside of the 5.75" backfocus spec, this is a visual scope.? I can get a good collimation on the OUTSIDE of focus.? Secondary shadow is centered.? Will run towards focus, just out of focus, star "ring" is evenly bright.? Go INSIDE of focus, secondary NOT centered.? So I can make myself crazy trying to even things out.? I am thinking that the primary might be tilted slightly as there is image shift when using the "factory" focus (the mirror lock are backed off, when using the factory focus), so the primary wobbles a bit.

Question is, how to square the primary to the secondary.? Anyone have this issue and what was the fix?

Thanks, Mike?
 

My C 14 edge is about 10 rears old purchased when this optical system first became available. I have never touched the secondary! Factory alignment was perfect and has remained that way. It is observatory mounted and has never been transported. I suspect that your hunch is correct. The primary might be slightly tilted. I don’t think that can be addressed except by Celestron. Lou
 

Mike, the secondary on the C14HD has been measured by a professional optical designer on CloudyNights.com to be a sphere to a high degree of precision. This means that it has no preferred axis and if it is decentered, you can achieve collimation by using its tip-tilt adjustments. A decentered secondary will give uneven field illumination (probably invisible to the eye but detectable by CCD imaging) and I think it will also result in what you are seeing. You can try physically measuring the secondary housing from the edge of the cell in several directions and see if it is off center. If it is indeed off center, there can be three possibilities: the secondary is off center (either in its housing or the housing is off center in the hole in the corrector), the corrector is off center, or you have a bad combination of both. Whether you should go to great lengths to fix this depends upon whether there are actual issues in the images in-focus.


On Sat, Dec 30, 2023 at 7:22?AM Mike Shade via <mshade=[email protected]> wrote:
So I have a C14 Edge.? I am having I think a centration issue.? I am using a Feathertouch focuser on the back end, screws onto the rear cell.? Collimation is after the scope has acclimated for several hours, Do not use a diagonal, straight through the back end.? Star at fairly high elevation.? Start at low power and work up.? The corrector was centered by the folks who sold it to me.? Using the primary mirror locks.? I am somewhat outside of the 5.75" backfocus spec, this is a visual scope.? I can get a good collimation on the OUTSIDE of focus.? Secondary shadow is centered.? Will run towards focus, just out of focus, star "ring" is evenly bright.? Go INSIDE of focus, secondary NOT centered.? So I can make myself crazy trying to even things out.? I am thinking that the primary might be tilted slightly as there is image shift when using the "factory" focus (the mirror lock are backed off, when using the factory focus), so the primary wobbles a bit.

Question is, how to square the primary to the secondary.? Anyone have this issue and what was the fix?

Thanks, Mike?

 

I have seen the material on CN.? When I purchased the scope a few years ago, the corrector was centered prior to delivery.? If it was centered prior to me taking everything apart is unknown.? What I was seeing was a clear difference between the outside/inside defocused images, the secondary shadow was off a bit between the two.? The rotational alignment was clearly off for the corrector, assuming that the sharpie mark on the primary is the alignment mark.? This will hopefully account for why this OTA is such an optical dog.? As for centering, I was thinking of putting a center dot on the secondary.? That might help.? As this is purely a poke around visual scope (have bigger and better OTAs for research purposes), not going to go nuts with it.? But it is a bother so will spend some time trying to get it figures out.

Thanks, Mike

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