Lens questions

Macro photography may be accomplished by mounting a lens in reverse, in front of a normally mounted lens of greater focal length. This method allows most cameras to maintain the full function of electronic and mechanical communication with the normally mounted lens, for features such as open-aperture metering.

The smaller the f-number, the larger relative aperture there is, and that means more light for the exposure. Each aperture has half the light gathering area of the previous one.

Small front lens elements are typical for macro lenses.

Such shallow depth-of-field is possible with lens of large aperture size (small f-number). The large aperture is a typical feature (and advantage) of a fixed focal length lens. The photo was taken with a 50mm f/1.4 lens.