How much of the field of vision is lost when one eye goes blind?

None. Your brain makes up for the lack of stimulus from a missing eye. You can try this yourself. Look at an object or a scene with both eyes, and then cover one eye with your hand. The scene or object will look exactly alike in terms of luminosity and clarity. The only thing that will be missing is the sense of perspective, which is why we have two eyes.

^^True^^ The brain only needs one eye for things like depth perception etc. The only thing lost will be the part of your range of vision beyond your nose on the half of the head not possessing an eye.