The angle of an object subtended at the eyes is the size of the object divided by the distance of the object from the eye. From the diagram below, this is
We are especially interested in how close the object can be to the eye and remain in focus. This is called the near point. For an object at the near point %theta is a maximum,
and
If a person looks at an object through an optical instrument, they see an image formed by the light after it has passed through the instrument. For the magnifying glass shown below, the angle subtended at the eye is
The angular magnification of the magnifying glass is the ratio of the two angles
and 