Help Celestron Nexstar 6SE focus issue

[yoda776]

Hi everyone,

I have a Celestron Nexstar 6SE with a focus issue. I have had a look at the collimation screws of the front of the Nexstar and have attempted to adjust. all seems fine with the artificial star set up and checking secondary mirror collimation (distance of artificial star as per manual). The issue is when I used the primary mirror focuser (rubber knob focuser). I can get the stars and planets to focus to a point but often there is a flare off to the bottom left and even looking at the moon, while there is no flare it just makes your eyes attempt to adjust to a slightly out of focus moon. Adjusting the primary knob backwards and forwards to the extreme to come back to refocus seems to demonstrate the scope can focus to a point. For instance, the trapezium of stars in Orion I can make out the four stars but they are fuzzy and cannot get them to focus properly.

There are a few little smudges on the glass with the secondary mirror, but nothing too significant. Also I can only find advice on collimating the secondary mirror which I have worked through already.

I only bought this new, however I bought it from the US, so the warranty is not going to work.

Does anyone have any ideas, routines / processes or advice on what to try? :help:

Cheers,
Matt

[yoda776]

Does anyone have any suggestions? I had one idea but it sounded a little bit far fetched. Not sure whether there is anything I can do but happy to hear any suggestions.
Cheers,
Matt

[Camelopardalis]

Matt, there's a chance you've got a duff one but unlikely.

A couple of things that could be affecting your ability to focus...

poor atmospheric conditions (seeing)...if you attempt to focus on a bright star, does it appear to be be pulsing irregularly around the centre, almost as if it's on fire?
thermal issues with your ota - give your scope adequate time to cool down to ambient temperature. You can see thermal currents in your scope as a kind of hazy view
collimation being far out? I'm not certain about this one. If your collimation is close but still a little off you will get flares on a bright star or Jupiter for example. Try dialling out the focus so you see a donut. Where is the dark hole located relative the the bright donut?


A few smudges on the optical surfaces shouldn't affect the image to this effect. The primary mirror moves when you turn the focuser and cannot be collimated, it's just the secondary with a SCT.

What eyepiece were you using when you see the symptoms as described?

[yoda776]

I am hoping it is not a duff one, but running out of ideas so the thought has certainly been on my mind. In answer to the points you have raised:
* While the atmospheric conditions were not ideal the stars were not pulsating.
* Good point on thermal issues - after fluffing around with it for a couple of hours I think it should have settled by then, but may try leaving it alone for a while to acclimatise. The interesting thing is I can see the cloud of orion however the trapezium of stars were all fuzzy and could not focus properly. Also tried going right to the extremes of focus and back through to focus.
* Collimation I suspect is just a little out and resulting in the flare, however I did go out of focus and the hole in the donut is in the centre. I was not originally, but had adjusted the secondary to bring it in line. The secondary was also suitably tightened on all 3 screws to maintain that position (i.e. did not leave any loose).
* The smudges I di not think so either, but just clutching at straws :P

Eyepieces used were -
* Celestron 25mm plossl (that comes with the scope)
* Meade 26mm plossl
* Meade UWA 14mm
* Meade HD60 12mm

I mainly stuck with plossls but tried all that I had and they all work fine on the other scopes I have (except the 25mm which I have only used for the Nexstar).

Thanks for the ideas and if you have any others - no matter how simple or complicated - please let me know. This scope is brand new apart from taking it out the box to attempt to view.

Cheers,
Matt

[raymo]

Have you tried the scope on near and far earthbound objects during
the day? If so is the whole field sharp like looking through one side of a pair of binoculars?
raymo

[Andy Walters]

Hi Matt,
this is a well known problem with the 6" celstron. Easy fix is to flock the centre baffle.
I still have some protostar flocking left over after doing mine if you want some. There is a thread about this over on cloudy nights.
Cheers Andy.

[yoda776]

Interesting idea. I might try that and see if I have trouble with terrestrial viewing. Not sure I have done this so will give it a go.
Cheers, matt

[yoda776]

Is there a link to the cloudy nights article you have on hand? I will try to view the site and see what I can turn up.

Is this the link?

http://www.cloudynights.com/topic/419728-flocking-a-sct-for-eliminating-halo-rings/

Be interested to know more about flocking.
Cheers, matt

[Camelopardalis]

The flocking might help if you're experiencing some baffle tube reflections but it shouldn't change your ability to find focus. Otherwise I'm stumped :question:

[brian nordstrom]

:) Sorry to hear your woes Matt , my C9.25 shows this as well , but that's only until it cools down properly , normally 3/4 hour or so , its quite horrible until then , how long have you left it out to cool before trying to observe ? .
Brian.

[yoda776]

I fluffed around with it for 2 hours after dark so I would have thought it should be ok, but could try again. Sorry to hear about your telescope as well Brian. Never knew so many people experienced this problem. I have other scopes and have not come across it before. Has me a little stumped :confused2:

I have thought about flocking but not sure how that goes. Done a little research and sounds like you have to do the inside of the tube within the telescope itself. Sounds a little risky if that is the case, although having said that the telescope is not much use as it is.

[yoda776]

It is an option I am looking into. Any place to go for information on how to do this? I also know it was not the night as I used the Meade ed80 and had no problems viewing (I.e. Atmospheric disturbances). I like challenges but this one is starting to look a little beyond it without trying flocking as the last resort.

[yoda776]

I tried again with collimating, but this time more on Venus and also Sirius and found the image was better. Allowed for the scope to acclimatise to temperature outside as well. It is useable now and reasonably happy with the effort I put in to get the result.

I may try to use a dew shield with flocking and see how I go in the future but for now it seems the fix I have currently has gone a long way. Not happy with the artificial star setup and may look further into that.

Thanks for the ideas and messages everyone. :thumbsup:

[Camelopardalis]

Nice one Matt, glad it's looking better. Ideally you need a night of good seeing to fine tune the collimating, and aim for a star around 2nd magnitude.

[Andy Walters]

Hi Matt, yes thats the report. When I got mine it was driving me batty worrying what was wrong with my brand new 'scope. I did flock all of mine, simply because of the amount of protostar I got!. But in reality to get rid of the flares you only need to flock the front edge of the inner baffle tube. It is very slightly tapered so it took me a few tries to get it right.(though I have heard of folk just putting a roll in from the back opening, however that ignores the the slight conical shape at the front end of the baffle. It's a lot harder to explain than to do.) I can send you a few square inches if you think it might help your problem. No need for glue or anything, it is self supporting.
Cheers Andy.

[yoda776]

Thanks - I am happier with the result. A suitable night might be a little way off with the weather patterns of late but will have another crack at it. I can see it is far better than it was but still not brilliant. Will try fine tuning and see how we go.

[yoda776]

Hi Andy,

The only thing that worries me about flocking is pulling apart the tube to apply it. When you say flock the front edge of the inner tube baffle it sound like you need to open the tube up to apply it. Is this correct? Might need instructions if applying this sort of material. :question:

Been just a wee bit apprehensive about opening an OTA, although I am reasonably handy with tools.

Cheers,
Matt

[Andy Walters]

Sorry for late reply!
yes I was full of trepidation before opening my tube to flock it, but as long as you make a mark to orient it back the same way you took it off, it was really easy. you have to take the vixen mounting plate off first if I remember correctly, (I have put tube rings on mine). And as I said I had to do it a few times to get it right!
Send me a pm if you need any more help or want some flocking (in reality you only need a piece about 30mmx 5mm to do the job).
cheers Andy.

[yoda776]

No worries Andy. I was going to try to fine tune the scope but have had no really good nights. I would try this first. Flocking sounds like an option I will need to do at some stage. I will take you up on the offer.
Cheers,
Matt