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Rangefinding with a MilDot Reticle
Understanding a MilDot Reticle
Many Riflescope manufacturers offer range finder reticles. The most common of rangefinding reticles is the Mil Dot Reticle. Range finding with a mildot reticle is a passive method and offers no external signature as a laser. Here, we will describe how to use a Mil Dot Reticle for range finding. A MilDot Reticle consists of crosshairs with milliradiansize dots evenly spaced across the horizontal and vertical axes.
The Geometry of the MilDot
To understand the setup of a Mildot Reticle, we’ll have to take a quick trip back to high school geometry. The MilDot Reticle is based on the Radian. A radian is an angular measurement of a circle where the radius of the circle equals the length of the arc of the circle. The Arc length to radius length ratio is one to one. A milliradian is one onethousandth of a radian and the arc length to radius length is one to one thousand.
Using the above geometry, we can then understand how the mil dot applies to range finding. The horizontal and vertical crosshairs each represent arcs of horizontal and vertical circles and the eye is the center of a circle. Next, we consider that the distance to the target to be the radius of the circle, then we will understand that the dot covers a portion of an arc of the circle. Now, knowing that the milliradian is one onethousandth of the radius, we can use the simple formula that a mil dot equals one unit per thousand units. So, a mildot represents one yard at a thousand yards; one meter at a thousand meters, or one inch at a thousand inches, etc.
Focal Planes
Rifle Scopes have two focal planes, called the First and Second focal planes. The Reticle can be located in either the first or second focal planes. When the reticle is in the first focal plane of variable magnification scopes, the mildot reticle can be used at any magnification as the reticle will shrink or grow with the magnification level. When the reticle is in the second focal plane of rifle scopes, the reticle size is fixed regardless of the magnification level. If this is the case, the mildot is usually calibrated for the highest magnification level. If you’re unsure contact the manufacturer or look at the manual that came with the riflescope. At the same time, testing the rangefinding system against a know target size can also reveal the calibration.
Practice,
Using a mildot reticle for rangefinding takes practice and a lot of it. In addition to understanding the geometry and use of the mildot, you must know the size of the target for comparison purposes. Try setting targets of known sizes at distances you think you may want to use the mildot rangefinder and observe them through the riflescope. Test what you see. Does it work? Does it make sense? It does? Great; now practice some more.
Finally,
Understand that MilDot reticles provide estimates for rangefinding. There are a lot of variables in play; the distance, target size, your eye. If you’re looking for precise rangefinding and have the time, you might want to consider a laser rangefinder.
Many Riflescope manufacturers offer range finder reticles. The most common of rangefinding reticles is the Mil Dot Reticle. Range finding with a mildot reticle is a passive method and offers no external signature as a laser. Here, we will describe how to use a Mil Dot Reticle for range finding. A MilDot Reticle consists of crosshairs with milliradiansize dots evenly spaced across the horizontal and vertical axes.
The Geometry of the MilDot
To understand the setup of a Mildot Reticle, we’ll have to take a quick trip back to high school geometry. The MilDot Reticle is based on the Radian. A radian is an angular measurement of a circle where the radius of the circle equals the length of the arc of the circle. The Arc length to radius length ratio is one to one. A milliradian is one onethousandth of a radian and the arc length to radius length is one to one thousand.
Using the above geometry, we can then understand how the mil dot applies to range finding. The horizontal and vertical crosshairs each represent arcs of horizontal and vertical circles and the eye is the center of a circle. Next, we consider that the distance to the target to be the radius of the circle, then we will understand that the dot covers a portion of an arc of the circle. Now, knowing that the milliradian is one onethousandth of the radius, we can use the simple formula that a mil dot equals one unit per thousand units. So, a mildot represents one yard at a thousand yards; one meter at a thousand meters, or one inch at a thousand inches, etc.
Focal Planes
Rifle Scopes have two focal planes, called the First and Second focal planes. The Reticle can be located in either the first or second focal planes. When the reticle is in the first focal plane of variable magnification scopes, the mildot reticle can be used at any magnification as the reticle will shrink or grow with the magnification level. When the reticle is in the second focal plane of rifle scopes, the reticle size is fixed regardless of the magnification level. If this is the case, the mildot is usually calibrated for the highest magnification level. If you’re unsure contact the manufacturer or look at the manual that came with the riflescope. At the same time, testing the rangefinding system against a know target size can also reveal the calibration.
Practice,
Using a mildot reticle for rangefinding takes practice and a lot of it. In addition to understanding the geometry and use of the mildot, you must know the size of the target for comparison purposes. Try setting targets of known sizes at distances you think you may want to use the mildot rangefinder and observe them through the riflescope. Test what you see. Does it work? Does it make sense? It does? Great; now practice some more.
Finally,
Understand that MilDot reticles provide estimates for rangefinding. There are a lot of variables in play; the distance, target size, your eye. If you’re looking for precise rangefinding and have the time, you might want to consider a laser rangefinder.
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Copyright 2009 MBS of New Orleans, Use with permission only.
Please visit our Sponsor, Clearly Optics.com
Copyright 2009 MBS of New Orleans, Use with permission only.
quickdraw62 
Latest page update: made by quickdraw62
, Sep 14 2009, 4:36 AM EDT
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