On Thu, 04 Feb 2010 03:46:01 +0400, "herschel@xxxxxxxxxxxxxxxx" <herschel@xxxxxxxxxxxxxxxx> wrote/replied to: >> >Why is there more DOF behind the point of focus than in front? > >Simple answer: DOF is related to magnification. Any lens shooting at, >say, 1:1 will give the same DOF. Higher Magnification= lower DOF > >So as things get further away the magnification drops and the DOF >increases. Subjects in the foreground blow out more because they're more >magnified DOF is sheer light physics, sometimes called optical laws. Something to do with circles of confusion, which is what gives us apparent sharpness. The circles of confusion get greater in a logarithmic scale from the camera out. The zone of apparent focus thus stretches further past the subject than in front of it. Not that any of the physics matter a hoot to a photogrpher, nor the terminology. The simple fact is 1/3rd in front, 2/3rds behind. I think the idea of magnification definitely comes into it, as the circles of confusion are greater closer to camera, and cover a wider area further away. Lens optical center to imaging surface dictates only one real focus point, where sharpness is maximum. The rest of what we call DOF is merely sharp enough for image viewing to our eyes. But you knew all this, and no I didn't explain anything, but it's fun postulating. -- Jim Davis, Owner, Eastern Beaver Company: http://easternbeaver.com/ - Motorcycle Electrics Check out my incredible fuse panel - the PC-8 is a hit! 1990 Honda VFR750, 1988 Honda Africa Twin 650
