The field of view of a telescope or a pair of binoculars is determined by its optical design.
It is usually notated in a linear value, such as how many feet or meters in width will be seen at 1,000 yards or 1,000 metres, or in an angular value of how many degrees can be viewed.
Generally, the more powerful the scopes magnification
the less field of view you will see.
See also:- What do the numbers on my scope mean?- What is magnification?- What is the field of view- What is an objective lens?- What is eye relief?- What is the exit pupil?- Twilight Factor- Relative Brightness