I hunted in Germany while stationed there years ago. I learned a lot about scopes and hunting, since the Germans hunt year round and hunt wild bore at night. Prior to going to Germany I hunted with Tasco scopes (thought they got the job done). After one month in Germany, all my Tasco scopes went into the garbage.

Two rules come into play when talking about low light transmission. First is the ratio of the scope magnification to the front objective. Second is the quality of the scope and glass in it.

The Europeans where hunting boar at night many decades before our modern night vision, so they needed optics with great glass and the right objective sizes. At night in the dark, the human pupil dilates down to about 6 to 7 mm. So one would want a scope that has an exit opening on the rear objective of at least 6 to 7 mm. Anything less would not let enough light through to match the pupil opening. Anything greater would allow the eye to see more.

The best combinations in fixed power scopes where 8X56, and 7x42 which were quite common in Europe. The magnification divided into the objective mm size equals 7, to match the eye opening. The 8X56 having a larger objective lens would let more light through.

This can be applied to variable power scopes also. A 3-9 X 40 scope would have eye exits of 13.333 and 4.444 respectfully. In low light on 3 power it would look much brighter than on 9 power the same light.

Then the quality of glass and coating come into play. Most of the European optic manufactures have very good reputation in this area.
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Dave