Photography

Any of the above problems is present to some degree with any lens. In the rest of this tutorial, when a lens is referred to as having lower optical quality than another lens, this is manifested as some combination of the above artifacts. Some of these lens artifacts may not be as objectionable as others, depending on the subject matter.

Note: For a more quantitative and technical discussion of the above topic, please see the
tutorial on camera lens quality: MTF, resolution & contrast.
INFLUENCE OF LENS FOCAL LENGTH

The focal length of a lens determines its angle of view, and thus also how much the subject will be magnified for a given photographic position. Wide angle lenses have short focal lengths, while telephoto lenses have longer corresponding focal lengths.

lens focal length diagram

Note: The location where light rays cross is not necessarily equal to the focal length,
as shown above, but is instead roughly proportional to this distance.

Required Focal Length Calculator
Subject Distance:
Subject Size:
Camera Type:
Required Focal Length:

Note: Calculator assumes that camera is oriented such that the maximum
subject dimension given by "subject size" is in the camera's longest dimension.
Calculator not intended for use in extreme macro photography.

Many will say that focal length also determines the perspective of an image, but strictly speaking, perspective only changes with one's location relative to their subject. If one tries to fill the frame with the same subjects using both a wide angle and telephoto lens, then perspective does indeed change, because one is forced to move closer or further from their subject. For these scenarios only, the wide angle lens exaggerates or stretches perspective, whereas the telephoto lens compresses or flattens perspective.