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Hyperfocal Cameras
The idea is to choose a focusing distance that maximizes the amount in focus at once. In practice this means from infinity to some defined near focus point.
One could use a normal photographic lens set to a hyperfocal distance and proceed, but this loses the "look and feel" of the pinhole camera and adds complexity to the design. Even though we are going to use a lens instead of a pinhole, it would be nice to maintain as much of the aesthetic of pinhole as possible.
50mm 2 element achromat @ F128 on Ilford Technical Film, Ortho, 4x5
I have been investigating using simple lenses for use in hyperfocal cameras. The simplest is a plano-convex lens. Curved on one side and flat on the other (|. These can be had from Edmund Scientific for under $20 [see their Industrial Optics catalog]. The next step up would be a two element acromatic lens, cost about $30-40. This offers superior color correction, but is unnecessary if we use ortho film, photographic paper or a colored filter.
Other possibilities include older lenses. I made one camera from a Zeiss Anastigmat, 75 mm, from 1891, found on a junk bench at a camera store. Don't overlook parts of lenses either. Taking apart an old 8mm movie camera will yield lots of fine optics.
Zeiss Anastigmat (made
in 1891), f128 2 seconds with 23a filter onto T-Max 100
4x5 is the easiest format for making these cameras. Film can be had from Freestyle Camera for very little money, including blue sensitive only ortho films. The only other supplies are a few film holders, used or in camera stores, and some black foam core board from an art supply store to make the camera itself out of. The camera is made in very much the same was as for a pinhole. [see making a 4x5 foam core pinhole camera]
Hyperfocal cameras work best in wide angle focal lengths. The advantage of a hyperfocal camera over a pinhole is shorter exposures and sharper focus. The disadvantage is too much light and limited focus range. In a pinhole camera you do not need to worry about focus at all. In a hyperfocal, there is a minimum focus. For a 50mm lens [extreme wide angle for a 4x5], the minimum focus is 1/2 foot. Not so bad. But by the time you get to 150mm [normal lens for a 4x5] it is now closer to 4 feet. Not so good if you are used to a pinhole camera.
Another factor is the positioning of the lens. In a pinhole camera, if you are off a couple of millimeters, so what. But in a hyperfocal camera, even a fraction of a mm off will ruin the effect.
The size of the F-stop is less of a problem, even though the table looks scary. If you are off a little bit here, it usually means just making some adjustment in the exposure. One source of F-stops are those electron microscope grids mentioned in the pinhole section [see suppliers]
If you want to see the math involved in generating these tables, see Hyperfocal Math [also useful if you want to use an existing lens on a 35mm - 8x10 camera, as a hyperfocal lens]
NOTE: Simple lenses, though a lot less expensive, are not the same as expensive large format lenses. Without all the corrections of the higher priced lenses, the simple 1-3 element lenses project a different kind of image. Space is not flat, but rather curved. The area of sharpest focus will be different at the center of the image than at the edges. If a lens does not "work" for you in one orientation, try flipping it over, so the curved side is towards the subject or now towards the film. Like the artistic "Holga" camera users, do not be afraid to experiment and see in a different way.
Hard Contact lens, +13
diopter (77mm) behind a diaphragm from Edmund scientific. f128 1/2 second
on Ilford Technical Ortho film (4x5). [lens was ordered from my optometrist,
about $70]. Actual image is much sharper than appears here. Right is a closeup
of the birds on the rock in the center. Note: this lens must be used stopped
down. Wide open it is REALLY bad! Might make a good portrait lens, where one
could control the amount of unsharpness by the aperature. Below is a lens
image of the contact lens mounted behind a diaphragm. Contact lens faces the
film, diaphragm to the outside. Actual size of lens is about 1/2 inch in diameter.
Tables: [4x5 camera]
Lens extension, mm FL (mm) F90 F128 50 58 62 55 63 67 60 68 71 65 73 76 70 77 81 75 82 86 80 87 91 85 92 96 90 97 101 95 102 106 100 107 111 105 112 116 110 117 121 115 122 125 120 127 130 125 132 135 130 137 140 135 142 145 140 147 150 145 152 155 150 157 160
FOCUS: [in feet!]
Focus camera at: Near Limit of Focus FL (mm) F90 F128 F90 F128 50 1.2 0.9 0.6 0.4 55 1.5 1.0 0.7 0.5 60 1.7 1.2 0.9 0.6 65 2.1 1.4 1.0 0.7 70 2.4 1.7 1.2 0.8 75 2.7 1.9 1.4 1.0 80 3.1 2.2 1.6 1.1 85 3.5 2.5 1.8 1.2 90 3.9 2.8 2.0 1.4 95 4.4 3.1 2.2 1.5 100 4.9 3.4 2.4 1.7 105 5.4 3.8 2.7 1.9 110 5.9 4.1 2.9 2.1 115 6.4 4.5 3.2 2.3 120 7.0 4.9 3.5 2.5 125 7.6 5.3 3.8 2.7 130 8.2 5.8 4.1 2.9 135 8.9 6.2 4.4 3.1 140 9.5 6.7 4.8 3.3 145 10.2 7.2 5.1 3.6 150 10.9 7.7 5.5 3.8
Size of F-stop (mm):[lens extension taken into account]
FL (mm) F90 F128 50 0.64 0.48 55 0.70 0.52 60 0.75 0.56 65 0.81 0.60 70 0.86 0.63 75 0.92 0.67 80 0.97 0.71 85 1.03 0.75 90 1.08 0.79 95 1.14 0.83 100 1.19 0.86 105 1.25 0.90 110 1.30 0.94 115 1.36 0.98 120 1.41 1.02 125 1.47 1.06 130 1.52 1.10 135 1.58 1.14 140 1.63 1.17 145 1.69 1.21 150 1.75 1.25