This eyepiece is really best for alignment purposes. The image is dim and eye position is critical. This is expected due to the short focal length. However, it's advantages outweigh these factors. The double cross hair and ring are etched on glass and illuminated from the side with an externally powered 12V source. The position is adjustable with an X-Y screw arrangement working against a spring loaded plunger on the opposite diagonal. This leaves the center of the image open for exact alignment. The cross hair image has it's own focus adjustment. This is a far better scheme than the standard crossed wires mounted at the focal plane.