This is the ratio of the apparent size of an object in comparison with what a viewer sees with the naked eye. For instance, an object 1,000m away viewed through a Fieldscope with 50x eyepiece looks about equal in size to an object 20m away viewed with the naked eye. The magnification can be changed with a mounted eyepiece.
Calculation of magnification:
- Magnification= Effective objective diameter ÷ Exit pupil diameter
= Focal length of objective lens ÷ Focal length of eyepiece lens