Originally Posted by
Ulophot
Friendly note: Optical and related formulae offered in response to this question may serve others, but will be out of reach for me.
Question: Doesn’t depth-of field follow a widening curve, rather than straight lines, with increasing distance? Is there some region of change in this, perhaps around half the hyperfocal distance (just guessing?)
Reason for question: When I first read Stroebel’s View Camera Technique long ago, I was struck by illustrations that showed the DOF widening out like a trumpet bell as distance increased. As I thought about it, that made sense, since the increase of DOF as distance increases does this, as shown with an online DOF calculator; for instance, doubling the distance each time (with focal length and aperture constant). I later purchased Merklinger’s Ins and Outs of Focus, in which his lines are always straight. Given his elaborate calculations (which I had to skip over), I hesitate to imagine that his illustrations contradict the data. But, leaving aside the special instance I know of, that DOF is reportedly equal before and beyond the plane of focus at very small distances, one of these gents must be more correct than the other, no?
Example: DOFMaster.com shows DOF for a 50mm lens at f/5.6 progressing thus (distance in ft/total DOF in ft): 2.5/0.24; 5/1.01; 10/4.25; 20/19.7 (DOF increases slowly beyond a multiple of 4); 40/205.6; 80/INF (very rapid increase from 10 ft). Hyperfocal distance is 48.5 ft.
Bookmarks