Last weekend a friend gave me a five-minute lesson on optics which I found tremendously helpful. You may recall I sent out a call for optics help a short time back and unfortunately the crickets are still chirping. I’ve done a bit of research since that lesson and while I am far from an expert, I know enough to be slightly dangerous. I was planning to spend this morning discussing parallax. Unfortunately it is more than I can type. The easy way to describe it is what happens when your eye is in a different position to the optic from where the reticle was zeroed. So let’s say you are dead nuts on at 100 yards and then you move your head slightly to one side or the other. The reticle may appear to be on target, but you will be shooting off target to the side. Now that I gave you the oversimplified version I suggest if you are interested in the topic you should take the time to read this series of posts on Opticstalk.com.
Below is a great photo from Re-Gun where the author had aimed directly at the phone jack in the center image. When the eye position is moved the reticle changes position, but in reality the gun is locked in place and the center of the jack is where the impact of the shot would be. His target was very close so the change in position of the reticle is small, but at 100 yards or more it could be dramatic due to parallax.