Editing Magnification (section)

===Magnifying glass===
The maximum angular magnification (compared to the naked eye) of a [[magnifying glass]] depends on how the glass and the object are held, relative to the eye. If the lens is held at a distance from the object such that its front focal point is on the object being viewed, the relaxed eye (focused to infinity) can view the image with angular magnification

<math display="block">M_\mathrm{A}={25\ \mathrm{cm}\over f}</math>

Here, <math display="inline">f</math> is the [[focal length]] of the [[lens (optics)|lens]] in centimeters. The constant 25&nbsp;cm is an estimate of the "near point" distance of the eye&mdash;the closest distance at which the healthy naked eye can focus. In this case the angular magnification is independent from the distance kept between the eye and the magnifying glass.

If instead the lens is held very close to the eye and the object is placed closer to the lens than its focal point so that the observer focuses on the near point, a larger angular magnification can be obtained, approaching

<math display="block">M_\mathrm{A}={25\ \mathrm{cm}\over f}+1</math>

A different interpretation of the working of the latter case is that the magnifying glass changes the diopter of the eye (making it myopic) so that the object can be placed closer to the eye resulting in a larger angular magnification.