With the Linhof M 679cc camera, interchangeable backs offer you the choice of a variety of formats. The Linhof M 679cc Depth of Field Calculator for 6x6/6x8 Formats assists you in choosing the correct f-stop for the depth of field (DOF) that you want when using a 6x6 or 6x8 format film back. This interchangeable calculator attaches to the base holding the rails and front and back standards, making it easy to optimize DOF.  A DOF calculator is available separately for a 6x9 format film back.