Middle age and the telescope

Middle age and the telescope: One unfortunate consequence of aging is a reduction in our eyes’ ability to dilate in the dark. By the time middle age arrives, our pupils may dilate to as little as 5mm, instead of the 7mm of our youth. Nearly one-half the light of the 7mm exit pupil of a long focal length eyepiece will fall on a middle-aged observer’s iris, rather than entering the 5mm pupil of his or her eye, and consequently will be wasted.

If you’re middle-aged, then, buy very low power eyepieces primarily for their wider fields of view. Don’t buy them for brighter images if your eyes can’t dilate to match their exit pupil. Images are brightest when the eyepiece exit pupil matches your eye’s pupil.

. . . our 38th year