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celestron nexstar 8se eyepiece not clearing mount solution


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The instruction manual and all the videos I saw on setting up the telescope ALL showed the OTA already attached to the fork arm mount, and just talked about setting it all on the tripod's three bolts. There were no instructions on attaching the OTA to the fork arm mount. Since my OTA and mount arrived in separate boxes, I had to figure out for myself how the tube slid into the mounting bracket on the arm of the fork mount and secured with the clamp and large quick release knob.

So far so good, until I realized the standard diagonal eyepiece would hit the mount if it tried to move through the zenith.

So I started reading forums on the subject and after hours of searching and reading, although many others had the same problem, the only solutions discussed were to go buy special "short" diagonals, or just avoid the zenith altogether, which just didn't seem right on such an expensive high precision instrument, but hey, what do I know?

After using the scope like this for a while, I finally found the solution in a totally unrelated post.

BEFORE ATTACHING THE OPTICAL TUBE ASSEMBLY TO THE FORK ARM MOUNT, USE THE HAND CONTROL TO ROTATE THE UPPER ALTITUDE GEAR WHEEL UNTIL THE TWO "INDEX ARROWS" ARE ALIGNED WITH EACH OTHER.

This allows the tube to slide more forward in the mounting bracket so that it clears the base of the mount no problem. Why this is not mentioned in the manual or in any of the videos I don't know. Anyway, hope this helps...

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Hi, and welcome to SGL.

Yes, the scope can be slid forward. This does affect the balance, but when used purely as a visual instrument, this is not a major problem.

I think the problem essentially is that this mount was not designed for this scope. It is exactly the same mount (including size) that is used for smaller SE models (certainly identical to the 6SE, which I have owned) and there simply isn't enough room for the ota. If the scope is moved far enough "forward" for the diagonal to miss the base of the mount when pointing at the zenith, it is not now possible to rotate it so the front of the ota is pointing downwards for storage without shifting the ota again.

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Good point, D.

I guess the eyepiece clearance would probably take precedent, as it could happen accidentally, in the dark, whereas parking the tube straight down could be done in better light and more controlled circumstances, and probably a lot less frequently, unless you always point it down after every session. Is there some reason it should be pointed down after every session?

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It is exactly the same with my 9.25 Evolution too and whilst you can move the OTA forward, it does put it way out of balance, with just the diagonal and eyepiece, which makes me nervous about any extra/unnecessary strain on the gearing. It seems to me to be a design fault and my only complaint about the scope. Worse still the mount for the 9.25 is specifically designed for it! What were they thinking? ?

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8 hours ago, rjkh said:

Good point, D.

I guess the eyepiece clearance would probably take precedent, as it could happen accidentally, in the dark, whereas parking the tube straight down could be done in better light and more controlled circumstances, and probably a lot less frequently, unless you always point it down after every session. Is there some reason it should be pointed down after every session?

Well, I find it easier to carry in and out of the house and fit to the tripod that way. I suppose the same would be true if I ended with it always pointing upwards towards the zenith - TBH I had never considered that option. That would mean that the entire thing was always way out of balance, even when not in use. Would this increase the likelihood of damage to the gears if it got knocked? I'm nowhere near enough of an engineer to be able to answer that question!

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After a short session tonight, I have come to the conclusion that the mount, ( on my 9.25 Evolution anyway, ) Has a serious design flaw. If this had occurred to me earlier, I am afraid I would have seriously considered returning the whole thing. ?

The scope is great, the mount is great, but they just do not go well together. They really should have designed it so the OTA can move anywhere without catching on the mount, to fail to do so is very poor imo. Tonight I set up knowing I could not go anywhere near the zenith, so set up fairly well balanced and set the slew limitations to not go above 63 degrees. This because the limit seemed to be about 65 degrees or so, so I added a little leeway. It has worked that way in the past, with the settings in Skyportal. Not tonight. I had a little session then left it running, partly to test it, partly to watch Dr. Who! ?

I came back out afterwards to find the OTA jammed against the mount! OUCH! ? I am not impressed, surely if the software has a setting to get around Celestrons poor design department, it should, you know work. I will have to work out how to balance the OTA now, much further forward, so everything clears the mount. All it needed from Celestron is making the arm of the mount say 10 cm longer. I may have to send an e mail.

Annoyed; from Cheshire. ?

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