• "Aperture is aperture"...no accounting for film format
  • "FL is FL"...no accounting for film format
  • 'lens distance from rear node to film plane'...often does account for format. For example, a 200mm lens for 135 format is usually a 'telephoto' optical design, where the distance from rear node to film plane is shorter than the true FL of the lens; but for large format, a 200mm lens is not 'telephoto' in design, but a 'long focus' design. For large formats, a 'telephoto' design might be used only when the bellows length would be an issue.
  • The illuminance at the film plane of a 210mm set at f16 is NOT going to be a whole lot less (one-fourth) if the lens covers 8x10 as opposed to 4x5. The illuminance is the same, the size of the image circle is larger for 8x10 coverage than if the lens were designed only for 4x5 coverage.