Calculating exposures for your pinhole camera can be difficult. The
Lensless Camera Mfg. Co., whose models we sell, has provided us with the
following table of apertures and f-stops for their products.
Please note that the format (4x5, 5x7, etc.) of the camera is irrelevant;
only the working aperture and focal length determine the f-stop.
| |
| Focal Length |
Pinhole dia.
(thousandths) |
Pinhole dia.
(fractions) |
F-stop |
| 675mm/27" |
0.0156" |
1/64" |
f/2000 |
| 450mm/18" |
0.0156" |
1/64" |
f/1200 |
| 300mm/12" |
0.0156" |
1/64" |
f/840 |
| 225mm/9" |
0.0156" |
1/64" |
f/630 |
| 200mm/8" |
0.0156" |
1/64" |
f/560 |
| 150mm/6" |
0.0156" |
1/64" |
f/420 |
| 100mm/4" |
0.0156" |
1/64" |
f/280 |
| 75mm/3" |
0.013 |
1/77" |
f/230 |
| 50mm/2" |
0.013" |
1/77" |
f/154 |
Normal light meters do not, of course, work with abnormal cameras, but a relatively
simple calculation will permit you to meter for a larger f/stop and convert
the time given to one suitable for your pinhole camera. If you:
- set your light meter to f/stop A,
- it returns time S, and
- your pinhole camera has aperture B,
- you can find the correct exposure time X with the following
formula:
SB²/A²=X
The resulting time will generally be very long, so you will have to adjust
for reciprocity failure; unfortunately, different films require different adjustments,
so you will have to determine the proper formula from the tech sheets for the
film you are using. A rule of thumb for most black-and-white films is as follows:
- For exposures between one and ten seconds, double the exposure time
derived from metering
- For exposures between ten and 100 seconds, increase the exposure five
times
- For exposures of over 100 seconds, increase the exposure twelve times
(or, as Lensless Camera Mfg. Co. recommends, "open the shutter and go have
lunch")
Pinhole Conversion Chart for Needle Sizes
As seen in Jim Shull's "The Beginner's
Guide to Pinhole Photography" |
| Needle No. |
Diameter |
Best Focal Length |
F-stop |
| 4 |
.036" |
20" |
f/550 |
| 5 |
.031" |
15" |
f/490 |
| 6 |
.029" |
13" |
f/450 |
| 7 |
.026" |
10" |
f/390 |
| 8 |
.023" |
8" |
f/350 |
| 9 |
.020" |
6.5" |
f/300 |
| 10 |
.018" |
5" |
f/280 |
| 12 |
.016" |
4" |
f/250 |
| 13 |
.013" |
2.5" |
f/190 |
The Lensless Camera Mfg. Co. of Santa Barbara's cameras are listed in our catalog
on our Pinhole Cameras page.
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