William wrote: > Depth of field is a factor of reproduction ratio and aperture. > Focal length doesn't enter into the equation.
No. DOF has everything to do with focal lenght. Reproduction ration doesn't eneter the picture even if the DOF scale on your lenses are decided with reproduction ratio in mind. DOF is the relationship between whats in the plane of focus and whats outside it. This ratio won't change regardless of how much you magnify an image. Sharpnes does change with magnification. Eg. a lens has a certain sharpness regardless of how much you blow up the image; same with DOF at a certain focusing distance, subject magnification (on film), and aperture. I mean, talking reproduction ratio into DOF definition is like taking reproduction ration into lens sharpness definition. By that definition my Limited lenses sucks because my 8X10 meter images aren't sharp! DOF is dependent on four things only: 1. Aperture 2. Focal length 3. Size of the subject 4. Camera and subject distance If you shoot the same subject at the same subject size (angle of view) with the same subject camera distance at the same aperture but with differnt focal lengths, you'll get different DOF. This is the effect we are discussing here. P�l
