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Equipment Discussions >> Refractors
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Jonas
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Reged: 04/23/06

Orion 120 ed focuser collimation new
      #2577331 - 08/12/08 06:41 PM
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How critical is the focuser collimation on these scopes. I just tested it via a cheshire and the circles were almost concentric but not quite bullseye and though close it was easily noticed. I could shim it but how critical is this collimation? I remeber seeing in Suiters book that refractors can take quite some miscollimation before the view is altered.

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Covey32
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Reged: 12/09/04

Loc: Georgia
Re: Orion 120 ed focuser collimation new [Re: Jonas]
      #2577612 - 08/12/08 08:45 PM
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For visual use, not very critical. If your Cheshire is as close as that you'll never see the difference. Good "snap" focus tells you if you are in the ballpark. If you have a laser, check to see where the beam exits and if it's off center see how much adjustment you can get by shimming the focuser. If your Cheshire shows good as yours does you are not going to be too far off.

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mysky
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Reged: 09/06/07

Loc: CN
Re: Orion 120 ed focuser collimation new [Re: Covey32]
      #2577639 - 08/12/08 08:52 PM
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yeah, it's not very critical in vision use.
When it's used in astrophotography, the focuser collimation is more important.

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Jeff B
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Reged: 12/30/06

Re: Orion 120 ed focuser collimation [Re: Jonas]
      #2578418 - 08/13/08 08:37 AM
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Quote:


I could shim it but how critical is this collimation? I remeber seeing in Suiters book that refractors can take quite some miscollimation before the view is altered.



Longer focal length (F10 and above) Fraunhofer and Baker archromats, being coma free, are indeed rather insensitive to mis-collimation. However as focal ratio decreases and you start pushing the ED designs, collimation very much matters. Depending on the design and how well the lens was assembled, I suspect you would see astigmatism and coma at high power if collimation was off. Just do a high power (300X and above) star test. If the images are not round when using 4-5 rings on each side of focus, then tweaking may be necessary, but do the star test first. If it comes out fine, then don't worry about it.

Jeff

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