Unless you gave them a good thumping, it seems unlikely that they would be in collimation one week and out the next.
Does this happen when you are looking at a stationary object or just while you are panning with the bin?
Do you get eyestrain? That's usually a good sign that your bin is out of collimation. Or if you pull your eyes back from the EPs and you feel "relief" from your crossed eyes relaxing.
Were you observing under sunny skies both times? Oh, California, guess that was a dumb question! Boy, those weatherman got it easy out there!
Or was the second time in the late afternoon or evening? I haven't tried the 10x43 model, but if the optics are similar to the 7x36 EDII, it probably has some distortion at the edges and pincushion.
I found that when it's sunny out, the "edge effects" are not that noticeable but when light levels fall, the edge effects became much more noticeable. I don't know if the 10x43 employes the same level of pincushion that the 7x does. If so, the effect of panning with a binocular with a large of pincushion can ironically have a similar affect of a bin with "rolling ball" and this can have a disorienting effect on some people.
Do a star test. Saturn is even better, with its larger angular diameter, you will notice if the planet is "double".
If you don't know where Saturn is, look at the bright orange star Arcturus. Look for the "Big Dipper" and follow the handle in an arc to the bright orange star, that's Arcturus ("arc to Arcturus").
Do you see one bright orange star or two stars or an elongated blob? Does the star focus into a fairly round object or a pinpoint? ("seeing" conditions will affect how finely you can resolve the star, but Arcturus shouldn't look like it has a twin).
If the star is round, then slowly pull your eyes back from the EPs a couple inches. Is the star still round?
If Arcturus is not fairly pinpoint (round, not flared or double) either when focusing on it or pulling your eyes back slightly from the EPs, then you probably have a collimation problem.
If the star test is okay, then you might be noticing the edge distortions while panning during the day. Find a nearby tree line and slowly pan across it all the way to the left and then right. Get a "heavy adjustment moment" when you start panning or reverse direction?
Look at a close by tree and tilt the bins up and down the tree more quickly. See anything "strange"?
If it passed the star test and you experience this "dizziness" only while panning or tilting as described, then it's the "edge effects" that you're noticing.
If it didn't pass, then you need a properly collimated pair of ZRs.
Brock
