• format is by far the most important factor in dealing with depth of field

• assume less depth of field with bigger film formats

• Since we know that the longer the lens, the smaller the angle of view, we know that to get the SAME IMAGE with the SAME ANGLE OF VIEW on both 16mm and 35mm film, we'd need to use a longer lens for the 35mm film. Since larger formats (i.e. the 35 mm) need longer lenses and longer lenses cause less depth of field, LARGER FORMATS HAVE LESS DEPTH OF FIELD THAN SMALLER FORMATS!

This picture shows a 16mm frame and a 35 mm frame with an image displayed over them. In order to capture the same part of the image with the 35mm film, we would have to zoom in or move in closer to the trees, both of which would decrease the depth of field.

SO...
Bigger negative = Less DOF
Smaller negative = More DOF