When shooting a subject greater than 10X the lens focal length (4x5 135mm = 5.1") a bellows extension factor must be applied to the camera exposure.

EXAMPLE: With a 4x5 camera and a 135mm lens, a subject greater than 50 inches from the camera will need a factor applied to either/or combined shutter speed and apature to achieve expected negative exposure.

BELLOWS FACTOR: From Ole Tjugen (oftjugen@online.no) on June 1, 2002.

*Bellows Extension Squared Divided by Lens Length Squared = Bellows factor*.

In the above example, a focused image of a subject longer than 51 inches from the film plane with a bellows 6 inches extended would require a bellows factor of 1.44 or one and one-half stop increase [(6X6) 36 / (5X5) 25] = 1.44 or 1-1/2.

In your estimation are these understandings of mine correct?