Miscellany   LIGHT: To see the circles clearly there must be a certain level of contrast, again to reduce strain on the eye and also to elude some of the tricksy properties of light. Below you can see that even though the rings are the same size, a decrease in contrast makes them appear different. (2) This problem can be solved by adjusting the rear iris to welcome or boot out more light into the eye, changing the front aperture thickness or size. Also, the use of a visor or blinder can control the amount of light from the firing line for a more dramatic effect from objects further away. Also, staring too long at an image, especially if it is very bright can cause an after-image. These are NOT good for shooting, in fact flash photography is prohibited on shooting ranges during and before matches. After-images are believed to be caused by chemical residue left behind on the retinal cells of the eye, continuing to mildly stimulate the optic nerve. Needless to say, this persistence detracts from the clarity of the image at hand, and can confuse you. CANT: Remember, all of this is being done in 3 dimensions, so movement in any axis can affect shot placement. Cant is the rotation of the gun along its long axis, whether it is rotated clockwise or counterclockwise. Although it may look the same through the sights, the bullet is still affected by gravity and will not meet up with the sight picture as the gun rotates. Many people use cross-hairs (like the ones above) or spirit levels (like in regular levels with little bubbles) to make sure cant is consistent.   MAGNIFICATION OF MOVEMENT: Just an idea of how movement affects shot placement. From a distance of 50 meters, 1 degree moved (or .0175 rad) will move the shot placement by .87 m!