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C14 Losing Collimation

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#1 HCR32

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Posted 30 August 2019 - 07:08 PM

So my scope loses collimation when I engage the mirror locks after collimation is successful. I’m going to put a Crayford on the back and lock it down then collimate that way I can see if it works. Ive got a suspicion  that when I screw down the knobs on the rods to lock the mirror there maybe a touch of tugging on the rods being clamped down. I believe the rods are somehow attached/fixed to the mirror cell. These rods move in and out only when the course focuser is used. When the rods are clamped the course focuser is tight and hard to move as the rods are holding the mirror in place. At this stage I’ve followed the process but stars appear like they have a small comet tail after collimation is done and I try to lock the mirror. Any one no any trick I don’t with collimation or am I supposed to chase it all night long. I forgot to mention that I’ve also found that the course focuser is adding to the issue with the mirror flopping around a fair bit when trying to re focus the star back into focus. Could the focus mechanism be the issue here and if so how do you tighten the tolerances? Is it a know issue for the course focuser to put misalignment into C14s after collimation is done and refocusing the star? I’m scratching my head here not knowing what can be causing it?? Mirror locks or focuser? That is why I’m opting to lock down the mirror and try using a Crayford for the process as this will not shift the mirror. If I’m still having issues would there be any issues with the mirror and whatever is cradling it and is there a fix for that or some type of servicing that can be done to tighten things down seeing it’s an old scope? 

Late 90s model C14 

 

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Edited by HCR32, 30 August 2019 - 09:20 PM.


#2 HenryB

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Posted 31 August 2019 - 10:11 AM

The only way I was able to keep my C14 Edge in collimation for all points in the sky was to lock the mirror, use a crayford focuser and then collimate in this configuration. Because of the weight of the primary, the supplied mechanics cannot handle the weight. Once this was done, I was very pleased with views at all points in the sky I view.



#3 Eddgie

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Posted 31 August 2019 - 10:24 AM

When you did your collimation, did you always approach final focus using counterclockwise rotation of the focuser?  If not, this is probably why your collimation changes.  If you approach using clockwise, the mirror can still settle when you let go of the knob.

 

The locks you are using work in the same fashion as the ones on the EdgeHD, which is that they apply pressure to the side of the rod.  This means there is no tugging or pushing on the rod.. You are pinching it laterally.

 

My guess is that you did not use counterclockwise, and your mirror settled more into the grease film before you were able to lock the rods.

 

Maybe not, but that has been my experience. 


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#4 HCR32

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Posted 31 August 2019 - 06:43 PM

Off memory I don’t recall but I will give it a go and see what the results are with both suggestions. While I have your attention what ep focal length do you guys find to be a good all round match under mort condition for a c14. I used a 36mm on jupiter the other night and felt it was the best one through the night. Seeing was good not great but good enough.

#5 HCR32

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Posted 31 August 2019 - 08:20 PM

Also just wanted to mention that the scope has bobs knobs on it and the are screwed down a fair bit there no way easy to twist when adjustments need to be done.

#6 gnowellsct

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Posted 05 September 2019 - 12:42 PM

Here try the appendix to this document  

 

Unfortunately this procedure is not available to the EdgeHD owners as their lock nuts have no dimples to tighten for a spanner wrench.  Maybe said dimples are on the side of the lock nut but I haven't had one apart to find out.

 

Greg N


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#7 HCR32

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Posted 14 September 2019 - 07:42 AM

Thanks guys for all your help. Collimation was a success but unfortunately Jupiter was showing very soft detail and sharpness was lacking. I’m not sure what this means about the optics of the scope but I know they are not suppose to be that soft. It’s unfortunate but I feel as though this scope has something beyond the need of an excellent collimation. Visual it was disappointing. Just for the record I had a catcooler running on the scope for an hour and temperature delta was minimum during the night. Collimation was as good as one could get it. On a positive the information given here by you guys helped me hugely in learning how to deal with these big scopes.

#8 Bill Barlow

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Posted 14 September 2019 - 11:12 AM

Maybe the atmosphere had turbulence and affected the seeing?  When I previously owned a C14 I could usually get between 200-250X on planets most nights, sometimes more if the seeing was excellent.

 

Bill



#9 Eddgie

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Posted 14 September 2019 - 01:53 PM

I suspect that your seeing conditions are the primary culprit, and this would effect any 14" scope to about the same degree.

 

If you use high power on a star and you cannot see the spurious disk with a steady diffraction ring, your scope will be working at less than full capability.   How much less depends on how far from perfect your view of the spurious disk and diffraction ring is.   

 

If the ring is in motion, but mainly intact, the scope will work at near its fully capability.

 

If the first diffraction ring is flaring, and breaking up, you can still do some high res work, but again, some performance will be lost.

 

If you cannot discern a first ring and the spurious disk is flaring and and bubbling or unsettled, you will be working at considerably less than the scopes full potential.

 

In the summer, I would have many nights where I could work at near the scopes potential, but this usually did not occur until after midnight, when the major heat plumes from streets, buildings, and driveways had dissipated.

 

In the spring and fall, when daytime temps were moderate and night time temps did not fall fast, I had many more nights of very good seeing.

 

The difference?  When seeing is bad, Ganymede and Io are fuzzy balls.  When seeing is good, you can resolve surface detail on Ganymede and albedo features on Io.   This is rare to be able to do, but I have done it using a C14. 


Edited by Eddgie, 14 September 2019 - 01:53 PM.


#10 HCR32

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Posted 14 September 2019 - 05:08 PM

Rings seemed pretty steady. More steady then last few times I’ve used the scope. Never pushed the scope as I used 40mm and 25mm ep. Everything about last night lined up, good temp delta, good seeing, and very good collimation. That’s why I’m kinda blaming the scope. As much as I don’t want to do that I can’t see what else it could be, my 10” has shown me more and I’ve taken extra care with giving the c14 a chance considering their temperament.

#11 mich_al

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Posted 14 September 2019 - 08:02 PM

Also just wanted to mention that the scope has bobs knobs on it and the are screwed down a fair bit there no way easy to twist when adjustments need to be done.

Plastic threads ?



#12 HCR32

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Posted 14 September 2019 - 09:26 PM

No they are metal

#13 HCR32

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Posted 16 September 2019 - 01:28 AM

The scope has a central collimation screw due to its age and was wondering if I leave it alone. I’ve attached a picture of the screw in question. 

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