Prismatic scopes

Compact optics that use a prism instead of an erector lens system: the body is short and the reticle is etched directly onto the glass.

How they differ from a red dot sight

The etched reticle remains visible even with the illumination switched off or the battery dead, and it stays sharp for shooters with astigmatism, who often see a blurred smear with a standard illuminated dot.

The trade-off is a shorter and less forgiving eye relief than a red dot sight: the eye needs to be in exactly the right position. The fixed magnification, usually low, helps at medium distances but slows things down slightly at close range.

To add magnification to an existing red dot sight, a magnifier is used instead.