[vash]

Eye relief. The distance your eye is from the scope for a perfect view. Handgun scopes have lots of eye relief. An arms lengths worth.

Rifles scopes have less. Several inches. I’m not bringing up scout rifle scopes to not muddy the water. You put your eye up hard to a rifle scope you can’t see a full picture. You need to be back a few inches.

Binoculars have very short eye relief.

I’ve “scoped” myself when I was younger. Shooting prone which can put your eye abnormally close to the scope.