This ratio is considered the ideal shape by some manufacturers and many photographers for both vertical and horizontal composition. IF benefits include focusing without changing the physical length of a lens body, faster focusing, reduced diameter of the focusing ring, closer minimum focusing distance, and aberrations corrected throughout the entire focusing distance range.
Illuminance is the term quantifying the illumination of, or incident light falling on a surface.
Image is a two dimensional representation of a real object, produced by focusing rays of light. Image plane is the plane commonly at right angles to the optical axis at which a sharp image of the subject is formed. The nearer the subject is to the camera, the greater the lens image plane distance. Impressionism is an art movement in which painters broke away from the techniques of continuous brushstrokes and clearly expressed detail. They were largely concerned with the effects of light and color.