TargetTalk

the topic is probably known to every competitive smallbore/prone shooter, but i am still in utter confussion, how to track a mirage and overcome it in a difficult match day. can anybody will care to throw some light.........

I think you could with a polarizer filter on your iris.

Yeaha polariser (or two) will help a great deal, I won't shoot outdoors without a polar iris.

Hi,
To track mirage you first must understand what causes it. It is caused by a change in density of the air. Mirage is seen as a shimmer down range. This shimmer moves upwards and in the direction of the wind. The problem is the apparent position of the target moves with the mirage and then you aim at the "new" position of the target and then miss the 10 ring.

There are two types of mirage, "dry" and "wet" mirage. Dry mirage is caused by the heating of the ground by the sun. Wet mirage is caused by the evapouration of the dew from the grass and ground early in the morning once the sun come out. Both dry air and wet air have a different density to "normal" air and will cause poi shifts.

To track mirage while shooting takes some observation and practise. Remember that you looking at the "air" between you and the target. You can focus your scope closer towards you so you can see the mirage but I don't bother these days, just look at the target and observe the edges. You will see one edge distorting, this is the downwind side, so this tells you this is way the mirage is running.

The harder the mirage is running (more wind speed), the more the target image will distort sideways. This all assumes you can see through your scope with your non-aimming eye while sighting, it takes a little practise but really pays off in light conditions as the mirage is much more sensitive than the flags.

One more comment; if possible, don't shoot while the mirage is "boiling" upwards, wait until there is some breeze so the mirage at least tracks in a consistant direction. Shooting during the boil can be hazardous to your blood pressure as shots appear in a random shotgun fashion.

Hope this helps
Martin

Some questions on mirage:

I have always assumed that the info on shooting mirage has come from the long range shooters. The targets for longrange are much larger than smallbore and the lower edge of the bull is much closer to the (heated) ground. When shooting 50m smallbore the bottom part of the bull is further from ground level and the distortion of the bull is much less.
Caused by:
Close to the groud there is only a horizontal wind possible therefore the bottom of the bull is distorted horizontally. Higher up, vertical updraft of wind is possible and the upper part and sides of the bull are distorted vertically - and when the wind increases, also sideways.

Are these assumptions correct???

Shooting at a club in the Netherlands only 10 miles from the North Sea, and at a range that is surrounded by concrete walls and bullet screens above the shooting lanes we encounter winds that are mostly more than 4m/s and winds that swirl in all directions at the same time. Practicing shooting with mirage becomes very difficult that way.

Is there an solid explanation why the position of the bull shift only upwards and downwind when mirage occurs?

Any comments apreciated.

Albert B
(The Netherlands)

I agree with Martin H in his great explanation of the mirage but not in the concept of wet and dry air.
The air always have water steam. Only varies his %. The evaporation of the dew from the grass and ground early in the morning gives higher % of water steam than heating of the ground by the sun. But the mirage effect is the same.
Be very carefull with the breeze when mirage is running. Mirage gives you high impacts but the breeze "drags" them more or less depending on the breeze speed. Little differences on the breeze speed gives big ones in the POI.
In my oppinion polarizer filters does not help against mirage.
Hope this help

Juan Carlos, I agree that pol. filters do not help in case of mirage. The filters filter out one direction of the lightwave - horizontal or vertical depanding on the adjustment of the filter. As the displacement of the bull is casused by defraction of light in front of the filter, the bull still seems to be in a different position than it actually is. (Light is not miraculesly bent back to its original path and direction by the pol. filter.)
Polarisation filter do help when light is scattered in all direction and a star-like glare exists, caused by water droplets in the air or on the surface of grass etc.

Albert B.

Albert B:

I am shooting usually at 50 and 300 m and, of course, the mirage has more influence at 300 m but, in my opinion, is the most difficult variable in 50 m shooting (specially in prone).

You say:"..... we encounter winds that are mostly more than 4m/s and winds that swirl in all directions at the same time. Practicing shooting with mirage becomes very difficult that way." I think the problem you are is the swirling variable wind.
When shooting with mirage and 4 m/s winds the mirage effect is reduced by the wind because it mixes air of different densities.

Martin H 's explanation is exact. The wet mirage has a similar effect to the fog. The difference is that it is more intense near the floor. It takes place in very humid days, in the morning, if the sun leaves the clouds and shine. A soft wind eliminates it. The form of combatting is: to lift the position (to shorten sling, to bring near the handstop, to lower buttplate); to use the yellow filter; to delay the first shots, in order to give it time so that it vanishes.
I would be interesting to know, in the case of the dry mirage, what corrections to make. In this case, to wait is not a good option.

Hi all,
What I guess I was trying to say about wet mirage is that when the sun hits all that dew and moisture you really do get a poi shift upwards as the grass dries out. Sometimes it takes a while to warm the ground up enough to get evapouration of the water started. In this case the poi shift is a slow gradual creep upwards and is sometimes blamed on poor sighting etc, anything other than mirage.

Another example of wet mirage is when it has rained and then the sun comes out, your poi shifts upward, but only as long as the sun is out. If the sun is blocked by the cloud then generally you get a poi shift back downwards when the evapouration stops.

As Juan Carlos pointed out, the big effect is that mirage doubles the effect of the wind, not only is the wind drifting the bullet but then you are aimming at a target image that is shifted downwind by approx the same amount as well. It becomes very messy.

I think also that the blurry target image that is seen under mirage conditions (esp hot dry days) also contributes to lots of poor sighting and an increase in group size as well. I feel having a slightly bigger foresight can actually help decrease aiming errors as you tend not to "follow" the mirage. This is where the polariser really helps as having a large foresight on a sunny day can reduce the glare to a managable level.
Martin H

The mirage stumps the image.

Like Martin B says "You can focus your scope closer towards you so you can see the mirage" or focus the target with bigger magnification.

Sometimes I can see the blurring target through the iris when mirage is running. I wait to see clear to shoot.

There is another type of mirage. We do at times night shooting and then there is at times as the air cools down a night mirage at distances of 25 yards and 50 meters

I think is the same mirage:
In the morning hot air goes up, you see the target higher and you shoot up.
In the evening cool air goes down, you see the target lower and you shoot down.