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Posted: 1/22/2011 11:13:37 AM EDT
| I have had an Aimpoint Comp M4 for a week, never used it. There is now a faint red line angled across the lower part of the lens. It appears brighter depending on the light and my eye placement. There isn't any scratches or defects or the lens. |
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Its basically just (red) light reflecting back to your eye from leaking into the tube from the back.
All Aimpoints do it some degree, but the larger lens ones are a tad bit more noticeable. Its because of how efficient the coatings are at reflecting back red light, if any light leaks through the back, it will reflect just the red-spectrum of light back. You should be able to see it grow larger or smaller if you move your eye perpendicular to the flat edge reflecting off the edge. When you're outside its almost never noticeable unless you have a sunset behind you 
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Normal for Aimpoints. Always there to some degree, but is really noticable when the brightness is turned way up and not focusing on something downrange.
My understanding as to what exactly causes it might be wrong, but from what I've gathered... The LED sits in a cutout at the rear of the tube (high & right as viewed from the rear). Where the cutout and tube intersect is an edge that can catch & reflect light. The front of the optic is coated to optimize the visibility of red wavelengths from the LED to your eye. looking in from front of Aimpoint: 
When light catches the diagonal edge, the reflection appears exactly opposite the LED (low & left) at the same angle. Due to the lens coatings, the slash always appears red no matter if the light source illuminating the edge is the LED itself or sunlight. Diagonal lit with LED: 
Diagonal lit with flashlight from the rear (batteries removed from Aimpoint) 
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