Use this tool to understand how various camera settings influence depth of field.
For a rough estimate of depth of field with cinematic lenses, one can use the lens T-stop to approximate the F-stop. Calculator uses the standard 0.001 inch circle of confusion for 35 mm theatrical projection (scaled accordingly for the various RED sensor areas).
Acceptable sharpness may vary depending on screen size and viewing distance. The most meaningful results will be obtained by comparing relative depth of field at different settings, or to known camera settings with existing footage.