Thread: Best 3-9x40 scope under $800?

That is why the old favourite 4*32 were so clear. 32 divided by 4 = 8, which provides more light than a young eye needs or can use. Aged eyes have a decreasing factor, say 5 or 6. Anyway, if eye is healthy a 42 m objective provides optimum useable light at 6*, no more. A 56mm objective will optimise at only 8*. In most cases invery dull light you are best to wind down a varipower to 3* or so in order to best see the target. The formula assumes good glass / lenses and coatings. Mediocre lenses reduce the effective efficient light "gathering" even more. So, ideal choices are 4*28/32, 6*42. 8*56 in minimal dull conditions.