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 Post subject: Eyepiece adjustment
PostPosted: Sat Apr 20, 2013 11:09 am 
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Location: Atherton
In my attempt at collimating my newtonian, I made adjustments to the three adjusters on the eyepiece. A mistake on my part and I need to start from scratch. The articles I've read on collimation don't mention this adjustment. Where in the sequence and what effect should I see. I've made a collimater based on the club's cheshire but I'm not happy with it as I can't see any of the primary mirror clips. Any advice please will be much appreciated. Bill


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 Post subject: Re: Eyepiece adjustment
PostPosted: Sun Apr 21, 2013 11:54 am 
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I am not sure what you mean by adjusters on the eyepiece - do you mean on the focuser? The focuser doesn't actually have to be at right angles to the tube. Some big Dobsonians actually tilt the focuser down to make it easier to reach. With Newtonians only the primary mirror has a center and optical axis. So as long as you are "seeing" the reflection of your eye dead centre in main mirror and the collimator then you are on axis. Centring the secondary is less critical and only effects vignetting, ie getting or not getting, a full cone of light to the eyepiece.


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 Post subject: Re: Eyepiece adjustment
PostPosted: Sun Apr 21, 2013 3:14 pm 
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Hi David. Yes it's the focuser. There are three pairs of screws. An adjuster and a locking screw. If it's not too critical to collimation I'll leave them for now. I'll need to contact Dean to see if the society's cheshire is available.
Thanks. Bill


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 Post subject: Re: Eyepiece adjustment
PostPosted: Sun Apr 21, 2013 3:30 pm 
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That's unusual. I would fasten them down flush so they cannot move.
I use a 35mm film canister with a hole in for collimating in conjunction with a central ring (adhesive punch hole reinforcement type) stuck in the centre of the main mirror. If you see your eye in the middle of the ring you are there.
You mentioned not seeing the mirror clips - you should see these if you rack the focuser in as far as it will go. The secondary should move back and forth, tilt and rotate. With that combination you should be able to position it to see the full mirror. Then look for your eye and tweek the main mirror adjusters until it is central.


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 Post subject: Re: Eyepiece adjustment
PostPosted: Sun Apr 21, 2013 8:28 pm 
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Thanks Dave. I'll do as you suggest with the focuser screws. I've already been up to Dean's for the cheshire collimator so I'll use that. A quick look just now shows that I'm way way out.


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