Interesting article. They explain exit pupil and relative brightness and describe a test you can do to see how much light is transmitted thru your scope.

The test is to cover the objective end of the scope with a piece of paper, then shine a flashlight thru the occular end and the paper will have the light projected on it. Measure the diameter of that projection in mm. That is the objective to use for calculating the exit pupil.

I did the test on my K4, WPI 8x24 binoc and Safari 8x30 binoc. Here are the results:

__K4 Scope:__

Diameter of the projecton is 37mm

actual magnification of the K4 is 3.7x

There for exit pupil is 37mm divided by 3.7 which = 10mm That's pretty good considering most people eyes can use only 7mm. I was happy about that!

The relative brightness is exit pupil squared which is 10 x 10 = 100. That doesn't mean anything to me, yet!

__Now the WPI binoc:__

Diameter of the projection is 24.6mm

magnification is 8, therefore exit pupil is 24.6mm divided by 8 = 3.1mm

Retative brightness is 3.1 x 3.1 which = 9.4.....that's a small number compared to the 100 above!

__The Steiner Safari:__

Diameter of the projection is 29.5mm

magnification is 8

Exit pupil is 29.5mm divided by 8 = 3.7mm

Relative brightness is 3.7 x 3.7 which = 13.6, also pretty small compared to the 100 of the K4.

If I did this right, my K4 scope is many times brighter than both of my hunting binoculars. Does this mean I need new binoculars?

Can someone explain what all this means?

Thanks,

Smitty

Edited by smitty