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.
This is my quick cheat table if I take my pinhole with me.
DETERMINING EXPOSURE TIME FOR PINHOLE CAMERAS You have to work with small apertures (high f numbers) and long exposure times and the reciprocity law failure (Schwarzschild effect) must also be taken into consideration.
Taking photographs with a pinhole camera is always something of an experiment and requires a bit of playing around. Achieving perfect results is not always the most important aim.
Many pinhole photographers simply use estimated exposure times. Also, many commonly used films have high exposure latitude and therefore are less sensitive to incorrect exposure.
One option is to prepare a simple table for each pinhole camera whereby the time measured by a light meter can be quickly converted to the required time for the given pinhole camera and film stock.
You can use the PinholeDesigner program to help you with the following calculation. f number In order to calculate an exposure time, it is important to know the f number of the pinhole camera.
Using a lightmeter the problem is that the high f numbers on pinhole cameras are not available on light meters. The way round this is to set the light meter to a different aperture, usually f 22, and then convert the measured exposure time for the aperture of the pinhole camera. This is done by dividing the f number of the pinhole camera by the f number set on the light meter; this number is squared and the result is used to multiply the measured exposure time.
For example, if the measured exposure time for f 22 is 1/60 second, the calculation for our pinhole camera with an f number of 250 is: (250/22)2 = 129. The measured time is increased 129 times, therefore the exposure time for the pinhole camera will be 2 seconds (rounded).
Reciprocity law failure (Schwarzschild effect) For long exposure times, usually for exposures longer than several seconds, it is necessary to extend the measured time. The majority of film stocks indicate in their specifications by how much the exposure times should be extended; if not you have to experiment.
Tips for correct exposures Choose a material with high exposure latitude, this increases the probability of obtaining a useful negative. In general, conventional light-sensitive layers (which do not use T-grain emulsions) have a higher exposure latitude, such as Ilford FP4 Plus, and also the majority of commonly used colour negative films.
Indoors the times are very long, often more than one hour. Usually, the only possible method to obtain a correct exposure is trial and error.
The sensitivity of the photographic paper is to be tested. The light meter should be set to somewhere between 2 and 10 ISO.
A good idea for simplifying exposures is to create a table for each pinhole camera and type of film stock.
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.
You invest in a camera, film, developing and scanning/printing to get an unsharp image.
But – it is fun. The unpredictability makes it very interesting.
The first things I learned:
Measure. Or play.
No sunny sixteen with these apertures for me. Be aware of the reciprocity of your film. Fomapan 100 is no fun here. E.g. Ilford Delta 100 is a lot more easy.
Get closer. Closer. Even more close. Closer! (From Andrew Bartram)
Use a tripod.
Trick your shutter. (e.g. finger cover the shutter, open shutter, exposure, fingers cover the shutter, close shutter) to avoid movement if exposure is less than 10 seconds.
Look for contrasty scenes.
The sun is your friend.
Relax. It is not sharp. It is ok 😉
Tips from Neil Piper (neilpiper.com): „ One of things that draws people to pinhole photography is the ‘infinite depth of field’ that the medium is able to capture. A lot of people assume that everything in the composition, from the pinhole to infinity will be sharp. The general consensus is that if you have the optimum sized pinhole for your cameras focal length, then everything from 20 x your cameras focal length should have reasonable sharpness. For instance. A pinhole camera, focal length is 50mm. Most online calculators will tell you that the optimum pinhole size for 50mm is around 0.3mm, give or take a few 0.01mms.
Your camera now has the optimum sized pinhole for its 50mm focal length and so the maths says that everything more than 1000mm away from the pinhole (50mm focal length multiplied by 20) should be of optimum sharpness. “