Although it is popularly referred to as perspective changes with focal length, the perspective is independent of the focal length. The perspective is only controlled by the distance to the objects. (With a wide-angle lens one tends to move closer to the object).
To keep this slightly on subject, the non-full frame digital sensors, for example the Nikon DX, do not change the perspective, just the picture angle. Since the diagonal is really the diameter of the image circle it might make more sense to discuss the viewing angle of the camera system and lens and how it compares to the human eye. If the focal length is equal to the image circle (diagonal), the picture angle will be 52.3 degrees. Someone previously mentioned the optimum viewing distance is 10"/25cm and the reasonably viewing size is also 10"/25cm. That would equal a visual viewing angle of 52.3 degrees and it matches the assumption made about the diagonal being a "standard" lens. Bertho =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
