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Message: <blockquote data-quote="Matt_RTH" data-source="post: 1578720" data-attributes="member: 53715">The spotting scope is an apt example, but it also illustrates truth in the exit pupil being every bit as important, again, on a sliding scale.First, the OP question is related to Exit Pupil or Mag. So isn't it better to check the answer to the question by holding one variable constant? If you have the two being variable, then the effect of mag vs. exit pupil is at best skewed.Which leads me to a point that anyone can with a spotting scope with a zoom can check.Every spotting scope I have used, except for really large, top notch/alpha types breaks down at about 45x (often before).  The view becomes unacceptably dark.  Larger scopes that number will be higher.  So if magnification, and only magnification improves what detail is visible, then a spotting scope should actually have a better image as one zooms in.  Yet in practice we know that in most cases, the opposite is true.  Not only does the angle of view become impractically small, the heat and atmospheric effects are more pronounced.  Yet in absence of those environmental concerns, the dimness of excessive magnification is easily demonstrated.  So exit pupil is obviously still important, with magnification.I would love to see a better solution to this than just Twilight Factor, which factors in exit pupil, mag, objective size and available light. This is probably more like a torque and horsepower relationship where minimums exist to achieve acceptable performance.  On one end you have the F1 cars running what, 15000 rpm and then on the other end you have a diesel truck running 1800 rpm and pulling a heavy load.</blockquote>

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