Archived posting to the Leica Users Group, 2003/04/25
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]On Friday, April 25, 2003, at 03:04 PM, Jim Laurel wrote: > Johnny, > I have two video cameras - a Sony PD-100, which uses 1/4" CCDs, and a > PD-150, which uses larger 1/3" CCDs. Now, when I put both cameras > side by > side on tripods, set them to the same aperture, and frame a shot > identically, the PD-150 picture exhibits markedly shallower depth of > field > than the PD-100. And when you do the same comparison with a camera > that has > 2/3" chips, again set to the same aperture, and with the subject framed > exactly the same, the 2/3" camera 's picture exhibits even less DOF > than the > other two. > > Why is that? The smaller chip requires a shorter lens to give you the same subject size on screen. Imagine a 35mm, 6x7, and 4x5 camera in the same setup, all with zoom lenses. You frame something using a 50mm lens on the 35mm camera. To get the same frame on the other two you'd need something like an 80mm and a 150mm respectively. At the same subject distance the 150mm lens has much less DoF given the same degree of magnification. Moreover, the subject is the same distance away from all of the cameras, but what is crucial in DoF is the RELATIVE subject distance, ie (subject distance)/(focal length) So, relative to the focal length, the subject is closer to the 6x7 camera and closer still to the 150mm lens, which is another way of explaining why the DoF is shallower. - -- John Brownlow http://www.pinkheadedbug.com http://www.unintended-consequences.com - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html