Depth of field is a function of the sensor size, the size of the aperture and focal length.
Film tends to have bigger image area, which means longer focal length, which gives shallower depth of field. (the bigger the film, the more resolution you have also)
Because large CMOS/CCD sensors are expensive most digital sensors are smaller than film. most dSLRs are APS-C sized, which is notable smaller than 35mm or "full frame" which is again smaller than medium format or 120mm those digital cameras are still notably expensive ($45k+) and less sensitive compared to film. 35mm DSLRs destroy their film counterparts now. Especially the nikon d800/600 and the canon equivalents.
It is, but when you take cropping into account it's like this: If I shoot 2 photos, one with a 50mm lens at f/2 on 35mm film, and one with a 35mm lens on APS-C, I need f/1.4 to achieve the same depth of field, because everything is smaller. The image will however be brighter, because I shot at f/1.4 (assuming ISO and shutter speed are constant).
It takes less light to illuminate a smaller sensor using a smaller lens (because the image projected on the sensor is smaller), so I need to open the aperture less to get the same f-stop number, but I have achieved less bokeh (more depth of field) at what is the equivalent f-stop of a larger lens in doing so. The bigger you need to blow up the image to fill the sensor, the dimmer it gets, so more open aperture to get the same f-stop, but your DoF is shrinking when you do so.
It took me a long time to wrap my head around it this far, let me know if I'm making sense. I'm rambling a bit because I've not had to put this into words before, and could be way off base.
Depth of field is a function of the sensor size, the size of the aperture and focal length.
Film tends to have bigger image area, which means longer focal length, which gives shallower depth of field. (the bigger the film, the more resolution you have also)
This image sorta explains it: http://blog.berniesumption.com/wp-content/uploads/2010/10/do... and http://s.hswstatic.com/gif/illustration-how-aperture-works-2...
Because large CMOS/CCD sensors are expensive most digital sensors are smaller than film. most dSLRs are APS-C sized, which is notable smaller than 35mm or "full frame" which is again smaller than medium format or 120mm those digital cameras are still notably expensive ($45k+) and less sensitive compared to film. 35mm DSLRs destroy their film counterparts now. Especially the nikon d800/600 and the canon equivalents.