Math/Optics: How can I derive the focal length of a lens from the magnification percentage of an image? [more inside]
Why does a good camera use more than one lens? and what is the physics phenomena associated with it?
Let's say I find a shiny spherical object and under point lighting, I move it very close to my eye. I then focus on the bright spot, but focus at a distance of 1-2 feet until the patterns are in focus. At this point, it looks like a bad microscope. Am I looking at part of my own eye? Is this a documented phenomenon I could read about?
Selective Depth-of-Field in Six Feet Under, and a question about lens flares. [more inside]