That was funny!
Thanks for popping the link in Mikey- when I was reading the post I was saying aaaaaarghhhh where's the link?!
This seems to be a bit of useful information. Collimation vertically seems to makes sense after he explained it. And I wish I understood what he meant by secondary shadow of moon re collimation.... what's secondary shadow exactly.
Can anyone explain? I'd like to give this a go sometime on my dob.
Quote:
The diffraction limited area is dead center in a properly collimated scope, but there are a large number of Dobs at liberty in the world where the mirror is not quite immobilized. This can affect collimation greatly or a little bit as the scope is moved up and down. And many Newt owners have the inadvisable practice of collimating with the scope in horizontal position, where the mirror places maximum stress on the sling, thereby insuring maximum movement of the mirror when the scope is raised to view.
If the mirror/collimation is a little bit off you may find that the paracorr cleans up your image a tad, which it should not. And so your best bet is to reach inner peace with this issue by swinging to one of the Galilean moons (or in the case of Saturn, a nearby star) and de-focusing to see unto the Fresnel rings. And if your secondary shadow is off center with the moon dead center, then your mirror has slipped; and woe unto you. For now you know you must collimate for an optimal Jovian view. And it is thus often the case: that he who collimates on a Jovian moon will have the best view. And the SCT owner who practices this will clean the clock of the Newt owner who does not: so be wary.
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