In this illustration the subject distance has been entered as 42 inches, the aperture has been entered as f/22 and the depth of field limits are displayed as 39 and 45.5 inches. These limits will be recalculated and displayed immediately if you change the focal length, aperture, or subject distance values.

 

Choose DOF

If you’ve selected “Choose” depth of field, you’ll next see the screen at right. Here the desired depth of field limits have been entered as 28 and 48 inches and the calculation shows that the aperture necessary to provide that depth is f/90, and recommends focusing at 35.4 inches, measured from the lensboard.

Again, changing the near and far plane specifications will cause the aperture and focus distance to be recalculated. In fact you can even go back to the first screen (tap the “Restart” button or choose “Constants” from the Category drop list) and change the focal length to see what effect a different lens might have.

Notice particularly that the aperture that’s calculated by the “Choose DOF” procedure will supersede any exposure values you may have entered previously and you will not be able to modify it without canceling the “Choose DOF” selection first.

For that reason, the next screen, the Working Data screen, will display the aperture that has been calculated by your choice of depth of field limits, but the aperture and speed selection fields are disabled. If you don’t want to use the recommended exposure and development data you’ll have to backtrack and cancel the “Choose DOF” option, or change the depth limit values, or the focal length.