Larry Bolch
Well-Known Member
Circle of confusion: n., a dozen optical engineers around a table arguing about depth of field.
The key point with DOF is that while it is quantified on hyperfocal scales on lenses or in the viewfinder, or on countless depth of field charts, it can not actually be quantified. It all depends upon arbitrarily defining a circle of confusion—which does not necessarily match the lens, camera or photographer's eye. Charts kicking around the InterWebs may go back to the 1930s and are based upon calculations rooted in the coarse grained high-speed ISO25 films of the time along with uncoated lenses. While there may be a formula, there is no standard, and the results of the formula will vary depending upon what you define as the diameter of the Circle.
If Fuji decides that they will work with a small diameter circle, depth of field will appear less. If Canon decides on a large circle, their lenses will appear to have much greater DOF at any aperture and focal length. Using the hyperfocal scale on a lens to zone focus, may or may not work, depending upon how much softness the shooter can tolerate. Neither company is right or wrong. They just began with different assumptions based upon the camera, lens and attitude of the person doing the calculating. At best they are a very rough guide. Nothing in photography is less absolute than DOF!
It would be simple if focus were like __|¯¯¯|__ with focus falling off abruptly, but it is not. If the hyperfocal scale shows that you have a depth of field from three to six feet, six-foot-six-inches will not be a whole lot softer than at six feet, and sharpness may still be acceptable for a given image, well beyond. It all depends on who calculated the scale and what assumptions they made.
How to deal with something so vague? Test, learn your equipment, decide how much softness you can tolerate. Develop a feel for what your camera can produce at a given aperture and a given range.
The key point with DOF is that while it is quantified on hyperfocal scales on lenses or in the viewfinder, or on countless depth of field charts, it can not actually be quantified. It all depends upon arbitrarily defining a circle of confusion—which does not necessarily match the lens, camera or photographer's eye. Charts kicking around the InterWebs may go back to the 1930s and are based upon calculations rooted in the coarse grained high-speed ISO25 films of the time along with uncoated lenses. While there may be a formula, there is no standard, and the results of the formula will vary depending upon what you define as the diameter of the Circle.
If Fuji decides that they will work with a small diameter circle, depth of field will appear less. If Canon decides on a large circle, their lenses will appear to have much greater DOF at any aperture and focal length. Using the hyperfocal scale on a lens to zone focus, may or may not work, depending upon how much softness the shooter can tolerate. Neither company is right or wrong. They just began with different assumptions based upon the camera, lens and attitude of the person doing the calculating. At best they are a very rough guide. Nothing in photography is less absolute than DOF!
It would be simple if focus were like __|¯¯¯|__ with focus falling off abruptly, but it is not. If the hyperfocal scale shows that you have a depth of field from three to six feet, six-foot-six-inches will not be a whole lot softer than at six feet, and sharpness may still be acceptable for a given image, well beyond. It all depends on who calculated the scale and what assumptions they made.
How to deal with something so vague? Test, learn your equipment, decide how much softness you can tolerate. Develop a feel for what your camera can produce at a given aperture and a given range.
