Author Topic: Despite best efforts to collimate scope, stars look like planets - suggestions?  (Read 5264 times)

iam4208

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This is a plea for help.
I was up at Harperrigg last night and got some help from Lorne to try and collimate my Dobsonian.
Despite thinking we had it dialled in, when trying to focus on stars they refused to go to a pinpoint.
Instead they looked like fuzzy discs, although we were able to defocus either side.
Lorne has suggested cleaning the primary mirror, which does look a bit dirty.
I will probably do that at the weekend, but if anyone has any further advice or suggestions, I'd love to hear them.

P.S. I have got hold of the AstroBaby collimation guide for when I put it back together.
Sky-Watcher Skyliner-250PX FlexTube Parabolic Truss-Tube Dobsonian with Baader Hyperion 36, 21, 13 and 8mm EPs and a 2x Barlow.
Telrad and RACI finder scope for finding objects the good ol' fashioned way:-)

blinky

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Strange......  Does not sound like a dirty mirror, sounds like it still well out of collimation.  I would give it another go, maybe try and get in touch with Cat (Spookycat) as she is a bit of a expert at it!

jamesg4128

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Don't despair Ian. I love newts but collimation is always a challenge. I'm with Craig on this one, sounds like the collimation is still out. Are you using a laser, if so is it properly collimated? Have you checked both mirrors as well? Could be secondary alignment issues (you may need a screwdriver to loosen and tweek the secondary as well as the Allen keys. If you are using a laser are you using a centring adapter as it have had many hours of fun farting about trying to align without being centred properly. I got a Hotech laser for Christmas and haven't looked back, worth every penny. Try off-focus alignment on a star also as it can sometimes be easier. If that don't work mate call in the Kat!
James

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SpookyKatt

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quick question....its a flex tube you have isn't it ?  Doesn't sound like a dirty mirror to be honest,
not sure how big the 'fuzzy disks' were but are you sure the upper part of the flex tube was fully
extended ?  It hadn't jammed a little short ?

Kathleen
« Last Edit: January 28, 2017, 08:59:31 PM by SpookyKatt »
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Lorne

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Katt
The tube was fully extended, we tried 2 lasers with the same results. We got the "airy discs" both sides of focus, where we then expected pinpoint stars we got discs.... strange! The mirror was pretty dirty too.



SpookyKatt

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Ahhh ok, cheers Lorne.
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iam4208

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Okay, thanks for the advice everyone.
I'll try the Astrobaby instructions during daylight or in artificial light and see how I get on, as that doesn't require a laser.
I'll be able to check the tube is properly extended more easily too.


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Sky-Watcher Skyliner-250PX FlexTube Parabolic Truss-Tube Dobsonian with Baader Hyperion 36, 21, 13 and 8mm EPs and a 2x Barlow.
Telrad and RACI finder scope for finding objects the good ol' fashioned way:-)

BeerMe

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Any luck Ian?


Been having a chat with the missus and I have the go ahead to save for an upgrade  ;D   hoping around April time, and hoping for the 10" flex tube you have.  With some luck, you'll be up and running at Harperrigg before then ;-)
Paul

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iam4208

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I haven't had a chance to tinker yet - too busy with malfunctioning bikes, computers and printers.
I'm off on holiday next week, so I might get to it when I get back.
I don 't feel as if I've missed any clear nights either, but this season has been really poor.
Sky-Watcher Skyliner-250PX FlexTube Parabolic Truss-Tube Dobsonian with Baader Hyperion 36, 21, 13 and 8mm EPs and a 2x Barlow.
Telrad and RACI finder scope for finding objects the good ol' fashioned way:-)

BeerMe

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I got an hour with my scope up in Dundee at the weekend, but that's been it for me.


I made an internal shroud for it too, and haven't had a chance to see if it's at all effective.  Supposedly there's a clear, cold snap coming so all is not lost just yet for this season...
Paul

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iam4208

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True.  It will probably be excellent while I'm away.
However, I'm going to Gran Canaria for a bit of sunshine, so I'm not too bothered - I know where I'd rather be right now ;D
Sky-Watcher Skyliner-250PX FlexTube Parabolic Truss-Tube Dobsonian with Baader Hyperion 36, 21, 13 and 8mm EPs and a 2x Barlow.
Telrad and RACI finder scope for finding objects the good ol' fashioned way:-)

BeerMe

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Seen a documentary recently (sky at night maybe) about the obs on Las Palmas,  supposedly situated amongst some of the best dark skies in Europe. 


Las Palms is worth a visit for that alone!  Anywhere in the Canaries is right now lol, have fun mate.
Paul

Heritage 130p and a few bits n [eye]pieces

iam4208

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I've had a great week here in Gran Canaria. Wish I had a scope with me as there have been some cracking clear nights. It's also funny seeing Orion so much higher up in the sky[emoji846]


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Sky-Watcher Skyliner-250PX FlexTube Parabolic Truss-Tube Dobsonian with Baader Hyperion 36, 21, 13 and 8mm EPs and a 2x Barlow.
Telrad and RACI finder scope for finding objects the good ol' fashioned way:-)

iam4208

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Okay, I finally managed to try and collimate the scope using the Astrobaby instructions.
Unfortunately, I have not managed to make any obvious improvement.
I am having some issues every step of the way, as follows:
First step is to get the secondary mirror centred over the focuser tube. I'm not confident I managed it.  I used the centre screw and brought the mirror up as close to the top as possible, then I used the centre screw to move it back down until it looked to me as if it was centred.  However, there was a wide range of positions where it looked okay. In fact it looked okay before I even moved it.
I then tried the next adjustment, which is to use the 3 adjustment screws on the secondary to move it until all the clips on the primary are in view.  I couldn't get all 6 clips in view.  I then tried moving the primary mirror as far back as possible, thinking it must be far too close to the secondary.  That really didn't make any noticeable difference. Nor did moving the secondary up to the top to maximise the distance between them.
I wet through the steps several times, but really didn't make any progress.  As you can imagine, this is extremely embarrassing, but I have no option but to ask for help, as I have missed a few clear nights.
So, is there anyone out there willing to help?
I can travel anywhere in the Central Belt between Glasgow and Edinburgh and I am willing to offer cash or alternative rewards for helping me out.
If nobody replies by the weekend, I'll be sending the scope away to get fixed.
Thanks in anticipation[emoji846]


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Sky-Watcher Skyliner-250PX FlexTube Parabolic Truss-Tube Dobsonian with Baader Hyperion 36, 21, 13 and 8mm EPs and a 2x Barlow.
Telrad and RACI finder scope for finding objects the good ol' fashioned way:-)

perthskies

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Canon Pete and Stuffedhaggis are coming over Saturday night to my place in Abernethy. Why not pop up and 3 heads are better than 1

Just a thought

David
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