The size of an exit pupil shows the amount of light that you'll get. Of course, more light means brighter image. You can calculate it if you like: Objective Lens diameter / Maginifcation = Exit pupil. So, with our binoculars above, we'd get 50/7 =7.1mm.
On average human eyes, pupils dilation have the capability to go up to 7mm. With 7.1mm, you can see very well in low light condition.
Twilight factor determines resolution, the higher it is the better the resolution. If you'd like to calculate this, just multiply the maginification power and the objective lens, squre root the result and you'll get the twilight factor.
This factor determines how well the binoculars perform in low light. To calculate this, divide the aperture or objective lens diameter by magnification and square the result. The higher it is, the brighter the images in low light conditions.
Field of View
How much of the area can you see through your binoculars? It's important for birders and hunters to follow movement of the subject. It is also great for binoculars used at sporting events.
|= objective lens / magnification power
|= √magnification power x objective lens
|= Exit Pupil2