DOF and Imager sizes
Posted 27 October 2010 - 01:47 PM
Posted 27 October 2010 - 03:48 PM
Hope this helps,
Posted 27 October 2010 - 05:17 PM
Practically speaking, the general rule is that the crop factor is also the number of equivalent f-stops you gain or lose in terms of depth of field (not actual exposure) once you match field of view and distance and f-stop.
In other words, if the difference is 2X (like the difference between a 12mm wide sensor and a 24mm wide sensor, let's say) then the DOF difference is two-stops, meaning that the smaller sensor would look as if you stopped down the larger sensor by two-stops in terms of the increase in depth of field.
A 2/3" sensor (about 9 to 10mm wide) has a 2.5X crop factor compared to a 35mm cine sensor (24mm wide), so the difference is 2.5-stops in terms of the increase in effective depth of field.
Posted 27 October 2010 - 08:29 PM
If you take a 35 mm sensor camera and a 1/3" sensor camera, put a 50 mm equivalent lens on each, set iris to f2 and focus on a human subject about 5 feet from the lens, you will see a huge difference in your depth of field, or appearance of depth of field. It's as simple as that. Scientific and mathematical mumbo jumbo aside, sensor size (or film size/format size) is a key piece of the depth of field puzzle, along with focal length and aperture.
Am I right in saying that smaller format has a smaller circle of confusion diameter, therefore more of the image is likely to be in "acceptable focus"? And with larger format, the circle of confusion diameter is larger, therefore out of focus areas will look really out of focus, giving us the pleasing out-of-focus bokeh that we all know and love? If I'm wrong ... oh well. I don't care about the technical stuff anyhow, just how to use it.