Is it all down to sensor size?

Mr. Hector

Mr. Hector

Active member
I would like to have the ability to achieve a shallow depth of field without having to have a 35m adapter with all its associated compromises.

If the dxx or hvx had a *Full frame* sensor, would the shallow depth of field and out of focus rendition I get from my 75m 1.4 rangefinder lens be possible, or are there other issues realating to the way digital sensors capture the light?
 
Nope. It's basically just the image plane (Sensor size) and the aperture.

Some people claim the zoom affects DoF but it actually doesn't. The DoF is the same but the "perceived" depth of field is shorter with a longer lens, simply because it compresses the space, so you see the out of focus background more.
 
Correct. For a given subject size, only sensor size and aperture determine DOF for a wide range of settings. Besides the "perception" issue, there is another element which makes the DOF story so controversal: Dof relates to the far distance DOF + the near distance DOF. Although total DOF (sum) is -over a wide range- lens focal length independent, the far distance DOF grows, and the near distance DOF lowers with shorter focal distance lenses. Because people often relate DOF with objects behind the focussed object, DOF (far distance DOF!) grows with wider angle lenses. If the focussed subject is positioned at the hyperfocal distance, the far DOF even becomes infinite (and so does the total DOF of course).
 
Long focal lengths are perceived as shallower also due to the limited field of view. You only see a very narrow area behind the subject, so whatever the focus of the background, it is magnified in a sense, resulting in shallower perceived DoF.

However, there is a trade-off in nearly all zoom lense. At max wide angle you can get a max iris, such as F1.6. However, at max zoom you have a max iris of usually F2.8. So, your shallower perceived DoF due to zooming in may be cancelled by an actual deeper DoF due to the smaller iris. Hmm.

You can use ND to control DoF, but it really only makes a marked difference outdoors. If a 35mm film shoot had to use F16 or F22 due to bright sunlight, and you could throw ND on your DVX to get it to a wide open aperture, the DoF would actually be quite similar. However, for most situations where a film DP is targeting an F2.8 or F4 aperture, you just can't match that without an adaptor no matter how hard you try.
 
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