Point The Lens: The focal length of a lens is a fixed characteristic that determines the point the lens at which a sharp image will be formed of an extremely distant object. Imagine the light ray from a distant point the lens as a lever, which is pivoted where it passes through the lens, and which continues until it forms an image. When the point the lens at one end of the lever moves, its image at the other end moves; the shorter the arm of the lever behind the lens ( a distance determined by the focal length), the less the image moves.
However, although a long focal length lens is mandatory, it need not be expensive. The utmost of critical sharpness in a portrait lens is not necessary, or even desired, since considerable diffusion can be tolerated in portrait negatives. Your lens needn't be in a shutter for strictly studio portraits, either. A lens in barrel is perfectly satisfactory, since you can provide yourself with a simple Packard shutter to use behind the lens. Many portrait men actually prefer the Packard to the more costly between-the-lens shutters.
This method will give you, contrary to a widely held belief, exactly the same perspective which you would have gained with a longer lens which covered the full negative with the same area you selected for enlargement. It is viewpoint the lens, not the choice of lens, which determines the character of perspective.
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Photography
