Here's a simple trick, if you wear glasses.
I've been through the right-handed, left-eye problem, because I used to shoot quite a bit, both with bows and shotguns, which have similar problems. The problem with shooting a shotgun, for example, where there is no rear sight, is that if you shoot right-handed, but your left eye is the master eye, you are looking slightly across the barrel at the target, rather than down the barrel. And you need to keep both eyes open for faster target acquisition.
Rather than trying to learn to shoot left handed, to match my left-eye tendency, I was shown a simple trick. Since you strive to make your shooting stance identical from shot to shot, you always look through the same place on your glasses. So the trick works like this: you mount the gun, take your right-handed stance, close your right eye, and then, with a pencil tip, figure out precisely where you're looking through your glasses with your left master eye. It will be a very small spot. With a shotgun, for example, it's usually the upper right quarter (with a bow, for me, it's usually left center, or slightly below center.) When you figure out that very small spot, you can put a tiny dab of Vaseline, or a very small piece of Scotch tape on that spot. When you then mount the gun, since you are looking for the target but can't see through that spot with your master left eye, your master eye will automatically shift to the right eye -- to the eye that can see the target. When I say a small piece of tape or some Vaseline, I mean SMALL. Smaller than a BB; more like the head of a straight pin. Since when you're just walking around, you look through the middle of your glasses, you're not even aware of the blind spot when you're not actually shooting.
I think this should work with cameras, too, if you tend not to look through the exact center of your glasses, but to cock your head a bit, to look at your target. With a little piece of tape, you should be able to force a master-eye switch.
I find with cameras, though, the problem is not as bad as with guns or bows, because you're looking down the tunnel of a viewfinder, and your eye/brain knows that. You should be able to shoot with either eye without too much problem; I suspect some people who think they are opposite-eyed actually are not, but simply have a stronger or clearer opposite eye, and so shoot with that by preference.
JC
