Hyperfocal Math All of these tables and formulas are derived from the formulas found in APPLIED DEPTH OF FIELD by Alfred Blaker, Focal Press, 1985, ISBN 0-240-51730-X NOTE: all formulas use millimeters as the unit of measurement. 1) First we need to define the "circle of confusion":
2) Assuming that the far focus limit is infinity the near focus limit is then [in mm]:
EX: so for a 4x5 camera with a f128 lens of 75mm focal length this becomes:
3) To find the lens to film distance: [NOT the same as focal length except in a pinhole camera]
EX: In the above the film to subject is the focus point or 687 mm, so
Now having said all that, here is an online calculator for the above: Tables: [4x5 camera][ALL units in mm]
This works great if you are building the entire camera, lens assembly and all, but what do you do if you already have the lens? The aperature values will be off. For instance, in the above, a 90mm focal length at F90, you would expect an aperature diameter of 1.000 mm, but the table shows 1.047, nearly a 5% change. Is this important? Probably not. Remember, F-stops are a 100% change (2x and 1/2x depending on direction). So, I would not sweat it. |