Looking the internet up I found some interesting thoughts
If you draw a ray diagram you may see a problem if you bring it very close to your subject, and your film sensitivity curve isn’t narrow.
For one thing the material in which the hole is made would need to be very thin, or you’ll get some odd vignetting.
But also remember that pinhole does a very poor job of focusing different wavelengths to the same plane. As the subject gets closer to the pinhole, that issue should get more noticeable: rays containing all the colours will need to approach the pinhole from more extreme angles.
Hence my suggestion to use a film with a narrow sensitivity curve… it’d be best if it were sensitive to a single wavelength
A very nice ultrawide pinhole camera from James Guerin at aupremierplan.
Here is his description the loading of this camera:
Curved film plane?
The film plane is curved to ensure even exposure across the negative, not possible with a flat film plane with such an extreme wide angle view (141° angle view of equates to a focal length of 6.4mm in 35mm terms). T
A side-effect of the curved film plane is that it results in a curved horizon in your photos unless the photo is taken with the camera level. This is why a precise bubble level features on the top plate of the camera.
CNC machined body
Curved film plane with a radius of 70mm (focal length).
Large 6x17cm (57x170mm) negative giving 4 shots per roll of film (120 roll film).
Angle of view: 141 degrees horizontal, 44 degrees vertical.
First I unscrewed the focussing ring (3 small screws to loosen).
Than a serrated focus ring has to be unscrewed anticlockwise after turning the „half a screw“ out of the way.
Now you can unscrew the front and the second lens anticlockwise.
Next the aperture ring goes of. From the back of the camera I now unscrewed the third, back lens, than a screw, than the bellow can be loosened from the shutter assembly from behind. A few small paper rings ( focus adjustment ) have to be carefully stored. From the front now i succeeded unscrewing the first and second lens en bloc, the grip I got with pieces of old bike tires. The shutter now free I used Isopropanol and a ultrasound cleaner for about 30 minutes, works like a charm now, than I used a little Silikon Spray on a toothpick to lubricate a few suspicious screws.
I still had trouble to separate the first/second lens element (they should allow to focus), heated them in the oven to 60 degrees Celsius, ultrasounded them, lubricated them, and soaked them in oil. Soaking in acetone finally loosened them enought.
Now they are seperated and the hardened green glue is completely removed.
And – finally – the camera is ready.
But – adjusting the focus comes first.
I taped a piece of transparent paper at the back ( where the film would usually be ).
Than I put the camera on a tripod and turned the front lens until a
skyscaper in about 800 m distance was sharp. Now I put the focus ring in
infinity position on and screwed it tight.
This morning I loaded a film and will take a few shots after work.
By the way :
Another victim of bellow – lightleaks told me to repair the bellows with McNett Aquasure, it seems to be a good glue and much cheaper than a new bellow…
Another tip is to oil the bellows with Ballistol, a well known weapon oil.
Interesting results are easy to get – use a pinhole…. I had gotten my hands on lots of old x-ray film. Expired since the nineties, but in lightsealed boxes. The format is 18×24 cm, so the cassettes fit in 8×10 large format cameras.
The 8×10 inch (20×30 cm) and the german 18×24 cm cassettes I got are very different, I had to mark them to load the matching film format.
If you construct a pinhole
the optimal pinhole size = 0,037 * SQR(Distance film to pinhole)
Aperture = film-pinhole distance / pinhole size
The projected circle of light from the pinhole = pinhole-film distance * 3,84 (using an 125 degree angle)
Exposure time = (exposure time aperture x) * (aperture pinhole / aperture x)2 (But I find usually I have to go with try and error, so take more cassettes than you think you will need or (like I do) load the cassettes on the road. I never know how much the Schwarzschild effect will kick in because I´m using old expired film. If you use documented film there will be a table in the documentation)
The following equation can be used to calculate the pinhole size:
where d is the pinhole diameter, c is a constant (usually Lord Rayleigh’s constant, which is 1.9), f is the focal length (i.e. the distance between the pinhole and the light sensitive material) and l is the light wavelength. The wavelength used here is yellow/green, which is 0.00055mm.
c. If you are not all that fond of doing the math youself, here is a table of a number of focal lengths, where you can find the number closest to your camera size and use as a guide when making the pinhole.