Hallo Mate
Remember when using high powered riflescopes, there will be an appearance of "darker on the higher powers" due simply to the
exit pupil and how the human eye sees the light reflected off what is being observed, then refracted through several lenses. To determine any optics exit pupil, you divide the size of the objective lenses by the ( power ) magnification. This will yield the exit pupil in millimeters. For the human eye to view all the light being transmitted through the scope, an exit pupil of about 4 millimeters is ideal. But when you are using high magnification or smaller objective lens, the exit pupil can get below the optimum 4 mm's in a hurry. This does not mean that you can no longer see the light and image transmitted, but because of the smaller exit pupil factor, the image appears darker.
For example:
Leupold 8.5x25x50 with a Premier Reticles 20 x 50 power boost
50mm objective divided by 20x magnification = 2.5 mm exit pupil
and / or
50mm objective divided by 50x magnification = 1.0 mm exit pupil
Nightforce 12-42x56
56mm objective divided by 12x = 4.6 mm exit pupil
and / or
56mm objective divided by 42x = 1.33 mm exit pupil
Those figures, combined with the knowledge that Nightforce scopes are equipped with excellent glass, will show that the Nightforce will convey a brighter image at its highest power setting.
However:
Leupold 8.5x25x50 with a Premier Reticles 20 x 50 power boost
50mm objective divided by 42x magnification = 1.19 mm exit pupil
Versus
Nightforce 12-42x56
56mm objective divided by 42x = 1.33 mm exit pupil
For a difference of 0.14mm's when set at the same power settings. Not really a whole lot of difference.
So, it's a give and take situation. Because of the larger objective lens and lower maximum power, the Nightforce will convey a brighter image, but at the expense of more bulk and a loss of the highly prized reticle set in the first focal plane.
My two cents is that 0.14mm's is not going to transmit enough light to justify the additional $1200 - $1500 USD's for a new scope. Nor is ANY daylight optic on the planet worth $4-5,000.00 USD's!