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exposure time - the formula

By the time you get some experience to approach the correct exposure time. But here again the spirits of divorce. Experienced hole camera photographers work with the feeling of not having the computer say some. The others prefer to rely on measured values and formulas.
The mathematical formula for calculating the exposure time is:

image distance divided by aperture diameter = light intensity.

on our example image distance (focal length) divided by 100 mm aperture diameter 0.3 mm is 333.33. must obtain in order for the pinhole camera from the exposure level to expand the scale of the exposure meter. There are also some templates, such as the slide rule by Dr.-Ing. A. Irmer as PDF file (see photo)












A measured exposure time of 1 / 30 sec. at f/22 in Aperture is 362 (the next value of f 333) 8 seconds. The wars, however, unfortunately not. Now comes to the Schwarzschild effect. For exposure times from 1 second, namely films behave differently than in "fast" times. One must allow for an extension factor that differs from manufacturer to manufacturer. In Ilford it is in our example, the factor 2 (8 sec). Our exposure time would thus be equivalent to 16 seconds. Fortunately, negative films are quite tolerant. But it's no good, reproducible results must be tested, or you have a very good "gut feeling"

The exposure helpers from the Web
There are some sites with small Java programs that help the exposure time calculation, and there are freeware programs you can download and install. The program is certainly the most versatile PinholeDesigner David Balihar.

the Pinhole Designer some popular films with previously unrecognized Schwarzschild correction are preset. The resulting times can secure a table.


is also very well done program by Michael Ratzkowsky "pinhole camera" . Also here you can print lists, taking account of the Schwarzschild effect common film marks are given.


For Mac OS X there is a pinhole calculator. PinholeCalc is a little freeware program that enables the to calculate all the important functions of pinhole photography, though not as extensive as the PinholeDesigner for Windows