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Old 08-10-2018, 06:43 AM
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multiweb (Marc)
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Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Quote:
Originally Posted by astronobob View Post
Marc, If I center the Spider hub by using calipers from the edge, then the 2ndry mirror is not in center as it is not mounted centered on the 2ndry mount, which is connected to the spider hub. Soo, I needed to 'off-set' the spider's hub to center the 2ndry, is this a 'no-no' ?
I ask, because I have heard of some 'Off-Setting' which needed addressing rgrds the 2ndary, not sure if that is to do with the actual 2ndry mirror or the spider hub ?

Stars Look the Same this 10" is now 'off' the mount, resting, I may make a ronchi tester, knife edge and light test for a better squizz at this mirror's shape ? ? or, I might ask here if any mirror-makers close by ?

Cheers mate
The secondary offset should be built in and the spider vanes should be kept square and centered as much as possible to avoid double diffraction spikes. Maybe the secondary has been moved and glued in a different position. The glass might also be stressed and why you're getting funny star shapes. Is it siliconed on the mounting? That's where I'd start looking.
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