1. The problem statement, all variables and given/known data - Why is it more useful to mark an objective lens [in a microscope] by its magnification rather than focal length? - Why might it be more convenient to think in terms of refractive power rather than focal length? [dealing with vision here] 2. Relevant equations - thin lens equation: (1/f) = (1/s)+(1/s') - magnification (m) = (-s'/s) - Refractive power (R) = (1/f) - Total R of eye = R(cornea) + R(lens) = 40 D at far point, 43.5 D at near point. - Total R = R(eye) + R(corrective lens) 3. The attempt at a solution - For the first question, I said that if you know m, then you could solve for the size of an object under a microscope pretty easily. Are there any other reasons that anyone could think of? - For the second, I honestly have no idea. To me, it seems just as reasonable to think about correcting vision in terms of the focal point of the eye/lens. I initially thought "well, glasses and contacts are in diopters, so it makes sense to think about correcting vision in this way," but couldn't we think of corrective lenses in terms of the focal point?