Twilight Factor

Here's one easy way to determine a scope's potential performance in low-light conditions.

Q: What do scope companies mean when they talk about “twilight factor”?

A: Twilight factor is a calculated number measuring low-light optical performance. It is obtained by multiplying the magnification of the optical system by the diameter of the objective lens in millimeters, and taking the square root of the product. In general, the higher the twilight factor number, the better the potential performance.

 

 

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