I've always wondered about this "simple" idea, and a student just asked
me. Magnifying glasses (biconvex lenses) are sold with a power rating (3x,
4x, etc.). How is this determined? Since m = -di/do, as do changes so does
di and m.
Is the di somehow a "fixed" value, corresponding to a person's near point?
And then the object is moved until it's in focus to find the "maximum"
magnification? If so, the m would change depending on the observer!
Wondering if someone has a simple explanation for this and/or an optics
demo related to this idea.