Re: Question on twilight factor how doe\'s one read the numbers?
Twilight factor is a marketing play on numbers that is close to meaningless. It's calculated by multiplying the magnification power by the objective lens diameter in millimeters then finding the square root of this product. Example: a 10 x 40 scope has a twilight factor of 20.
Twilight factors were originally used (I think) for binoculars but have also been used for other scopes. Higher twilight factors are supposed to indicate better image quality than lower ones when used at dawn or dusk (twilight time). A higher number usually means a brighter image but not always but has little to do with image sharpmess. In reality lens quality and how they're mounted and aligned do more to effect image quality than other stuff.