My understanding is that light transmission is capped at 8x. So for example a pair of Swarovski 7x42 give you 6x, 10x50 gives you 5x, etc… This is why the old straight 8 scope is the best light gathering scope you can buy, but you lose the ability to “zoom in”. All depends on what you want. I personally have multiple pairs of the 7x42 for myself and my family because they are good on a large food plot, but also good hunting the woods.
The maximum exit pupil and Young human eye will dilate is 7mm. Divide a 8X56mm binocular and this is the maximum a Young human eye will maximize any binocular for low light capabilities. It is more to it than this though. Build quality and lens quality, prizm quality, and lens coatings quality plus more other factors has alot to do with binocular low light capabilities.
