Just a quick comment on aperture that has been alluded to. Beginning photographers learn that a smaller aperture (larger number) creates an image with more in focus. This is frequently translated, at least in the minds of beginning photographers as the smaller the aperture (again larger number) the sharper the image. More distances in focus is not the same as "sharper image". Forgetting, for the moment, the range of distances that are in focus, both larger and smaller apertures cause unsharpness. Larger apertures use the more of the lens glass closer to the edges of the lens which because of the physics is not as sharp as the central area. Also when light passes the sharp edge of the aperture blades a portion of that light is refracted or bent which reduces focus. Since a very small aperture has proportionally more edge the image becomes less sharp. (Wow, this is getting wordy) The short ending...both very small and very large apertures create less sharpness and staying near the center aperture numbers creates the sharpest image. Yes, there are very good reasons for using both very large and very small apertures but it requires compromising sharpness.