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