[Major Dave (retired)]

between VX-1 and VX-2 is that the "2" has more/better lens coatings, resulting in better light transmission. Something on the order of 90% for "1", vs. 94% for "2".

The 50mm objective lens collects more light than the 40mm, resulting in a bigger "exit pupil" diameter. The bigger the scope exit pupil diameter, the more light goes into the pupil of your eye. In the early morning, when first light dawns, the pupil of your eye is wide open - about 7mm in diameter for young eyes, but us old farts pupils are limited to a maximum of about 4.5mm diameter. Therefore, any scope with an exit pupil diameter less than our wide open pupil will cause us to see a dim image in our scope.

To calculate the size of your scope exit pupil, divide the objective lens diameter by the magnification. Example: 50mm objective set on 5X magnification results in a 10mm scope exit pupil - 3mm bigger than the youngest eyes can use. 40mm scope objective lens set on 5x equals 8mm scope exit pupil. Again too much to be used, but not by much. So, at 5X magnification, both the 50mm and the 40mm objective lens will give a bright picture.

But, if you want to use maximum magnification in first light, the 50mm lets you do that. Example:50mm objective, 7X magnification, equals an exit pupil of 7+ mm. 40mm objective, 7X magnification equals less than 6mm exit pupil.

Once the sun comes up, you will still have some dimly lit shady spots where good light gathering optics are needed.