READING MIRAGE - Part II
Gene Beggs
Copyright© Precision Shooting Magazine 2004


“Reading Mirage” appeared in the January issue of Precision Shooting. In that article, I stated,

“Mirage blurs the target, making it more difficult and time consuming to establish point of aim, but in my opinion, based on experience and tests, it does not permanently displace the image, causing one to aim at the wrong spot.”

There are those who disagree, contending that mirage can permanently displace the target image.

For some interesting reading, go to Google.com, and search under “Optical Mirage.” There you will find an in-depth report by noted scientist, William Viezee. On page one, section VI, Chapter four, Mr. Viezee states,

“An optical mirage is a phenomenon associated with the refraction of light in the gaseous atmosphere. During mirage, a visible image of some distant object is made toappear displaced from the true position of the object. The image is produced when the light energy emanating from the distant source travels along a curvilinear instead of a rectilinear path, the curvilinear path, in turn, arises from abnormal spatial variations in density that are invariably associated with abnormal temperature gradients. The visible image of the mirage can represent shape and color of the mirrored object either exactly or distorted. When both the observer and the source are stationary, a mirage can be observed for several hours; however, when either one or both are in motion, a mirage image may appear for a duration of only seconds or minutes.”

This statement by Mr. Viezee, is a scientifically proven fact, but I do not believe that permanent displacement of the target image is a factor in short-range, outdoor target shooting. Mirage can and does displace the target image, but the displacement is only momentary. In my experience, the target image flickers in the direction of air movement, but soon snaps back to its true position.

For group shooting at one and two hundred yards, I use a dot reticle, centering the dot in the mothball. The eye naturally centers circles within circles. For sixteen years, I flew the Boeing 737 for Southwest Airlines, the flight director and heads-up display, in that aircraft uses a circles-on-circles presentation, so it is natural for me to center a dot in the mothball.

There have been times in which I have observed the two hundred-yard mothball flickering and bouncing as much as the width of the ring. If during such conditions, one were to hastily take aim and fire as the target image is momentarily displaced, he could easily induce a one-inch error. On the other hand, if he centers the dot in the mothball with small adjustments, and waits until the dot appears to be floating in the center, aiming error is minimized. Forget trying to obtain a razor sharp point of aim when mirage is running, it can’t be done! Insure that the dot appears to be centered in the mothball, but do not waste time trying to be too precise. Do your best, trust your instincts, and shoot!

One of the best training aids for reading conditions and establishing point-of-aim is the rail gun. Try the following experiment; I think you will agree. You will need a sturdy, immovable mount for both target and rifle. Remember that wind can deflect target frames, and thermal expansion can cause things to move; even concrete benches are not always rock solid. For my own experiments I used the following setup.

At the Midland Shooter’s range, slightly beyond the two-hundred-yard line, is a partially buried piece of earth-moving equipment; I figured this was about as solid as it gets, and taped a target to the side. At the firing line, I placed my rail gun on a concrete bench that had been checked for security. This was done in the cool of the morning, before mirage was visible. A precise point of aim was dialed in, centering the dot in the mothball.

Without touching the bench or gun, point of aim was monitored throughout the day. At times mirage was boiling, at other times running in one direction or the other, but at no time did the target image appear permanently displaced. The mothball flickered and bounced, but if one was patient and averaged it out, the dot always appeared to be floating in the center of the mothball. At the end of the day, after mirage had disappeared, point of aim was still right on.

These are the facts as I see them. You may draw your own conclusions, but I am convinced that permanent target displacement due to mirage is a myth.

In closing, I would like to caution you about a couple of things that can lead one to erroneously conclude that mirage is displacing the target image.

* Unstable target frames that shift position from wind pressure and forces induced by the moving backer system.

* Loose bench tops that move from the slightest pressure.