Cameras and Lenses
Collimation
For reasons that escape me, Iīve been playing with my binoculars to test collimation. The way I understand it (which is probably the "not at all" way), you cover the objectives alternately and see if the image "shifts" a lot. So anyway, it did. With every bino I tested. Anyway, the moon came up this evening. And on a whim, I covered each eye alternately (without binos), and guess what, the moon leaped from side-to-side. It also appeared to be slightly "double". Then I put on my glasses, and the moon wasnīt double anymore. And when I did the "alternate-covering-of-eyes" test, it didnīt leap as wildly from side-to-side, only a little. So I did the same test of my binos as earlier, but this time with my glasses on, and found they all appeared far better collimated than before without spectacles.
Does this mean:
a) Bad collimation may be a feature of oneīs eyes, not oneīs binoculars
b) Some of us need to wear glasses all the time while birding, even if our
prescriptions arenīt particularly strong
c) Iīve too much time on my hands
Try it yourself if you wear glasses. It really passes the time.
Stars work well. When your bins are out of collimation there are double stars all over the place.
[QUOTE=Sancho;1581996] Then I put on my glasses, and the moon wasnīt double anymore. And when I did the "alternate-covering-of-eyes" test, it didnīt leap as wildly from side-to-side, only a little. So I did the same test of my binos as earlier, but this time with my glasses on, and found they all appeared far better collimated than heretofore without spectacles.
[/QUOTE]
Check to see if either of your eyeglass lenses has a prism in it to correct a lazy eye. One of mine does. A prism will help correct the wild jumping you see without glasses. The way to check collimation is to put the binoculars on a tripod, make sure the binoculars are perfectly level, and look at a distant object -- I mean really distant -- so that there is no parallax. Then examine the scene through both left and right using the same eye (but not at the same time). 
If you see any difference in view between the two (whether left to right or up and down), then you have a collimation error.