Quote Originally Posted by bmac
Would the COF for 8x10 be 4x that of 4x5?

standard-COF is format_diagonal / 1500 - at least is this the one that is used to calculate most DOF-scales on lenses. However, this is a rather old convention (dates back to WW II) and film quality is much better today. For larger prints and/or more sharpness use anything between 1000 and 1300. However, an even smaller COF will unnecessarily decrease your DOF.