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Jeff Adams
newbie
Reged: 09/26/09
Posts: 1
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Can collimation test 'results' vary at certain points during the focus/defocus? That is, if I move through the focus range, can the system appear correctly collimated at close to maximum (the largest diffraction disk), but then as you focus it can appear unsymmetrical at some point? I'm quite a novice regarding the optics & mechanics of my scope, but I assumed that if collimation was off it would be visible throughout the focus/defocus range, getting more pronounced the further out of focus you get.
My system seems to be slightly off at lower out of focus but seems okay with a large disk. Apologies if I haven't used the correct terminology--hopefully my description makes sense.
Thanks in advance for your help. CN is a fantastic resource.
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brianb11213
Carpal Tunnel
Reged: 02/25/09
Posts: 2109
Loc: 55.215N 6.554W
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The symmetry of the disc pattern is more distorted by poor collimation the closer you get to focus. You can be way out of collimation & still see a "good" pattern a long way from focus ... as you get closer to accurate collimation, you need to get closer to the focus point to see any asymmetry.
If the collimation is perfect, the pattern will remain completely symmetric as you pass through the focus when observing with a very high power eyepiece. Any difference in the pattern inside & outside focus is incorrect correction of spherical aberration, not collimation - and almost all scopes will show it, especially if they're not allowed to cool to ambient temperature before testing.
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