Thread: Scope decision

Originally Posted by Marty Henry

Bigger objectives only allow you a little more magnification at last light

huh?

Originally Posted by chalkeye

huh?

optically the light gathering power of a lens is limited by the size of the eyes pupil. Fully open that's round 7mm. Simply put divide the diameter of the scope by 7 to get the maximum magnification that lets all the light gathered into the eye. For a 40mm scope that's 5.5x and for a 50 mm that's 7x. Transparency of the optical glass is particularly important as well especially transmission of the longer red end of the spectrum at dusk or dawn

Ah - you don't "get" more magnification, you get more light for a given magnification (with a larger objective). That was confusing.

Leupold