How choose a pinhole camera

The guide to know technical features about pinhole cameras

How working a pinhole camera

A pinhole camera is a simple photographic camera where the lens are substituited by a tiny hole called pinhole. Since the origin, pinhole camera was a simple hermetic box, usually with a parallelopiped shape, where in one side was be a tiny hole and in the opposite side was be placed the photosensitive support (film). Following this schema, in a pinhole camera, the light of the enviroment framed by the camera pass through the pinhole to project an inverted immage in the opposite side that will be exposed on the photosensitive support. This optical effect is known as principle of camera obscura, where the two main elements as pinhole and photosensitive support behave such as a human eye, in fact we can compare the pinhole at the chrystalline lens and the photographic support at the retina.

how working pinhole camera
"Sketch where is rapresented how working a pinhole camera thanks to the camera obscura principle"

Features that identify pinhole cameras

Exist a lot of different pinhole cameras models developed to execute different typology of photograpies. The knowledge of features that identify the camera allow at the photographer a good choice about the right device to reach the final result wanted. The features that identify pinhole cameras are the follows:

  • Focal length
  • Pinhole diameter
  • Film plane geometry
  • Number of pinholes
  • Immage format
  • Material which is made the camera
  • Pinhole shutter typology

Focal length

Focal length is the distance between the pinhole and photosensitive support. Are available pinhole cameras with different focal length and this feature identify their use, because the framing capability of the camera depends directly by the focal length. To understand better this concept is necessary thruogh an immaginary pencil join the pinhole center to photogram edges, in this way we going to obtain a piramid with the square base or rectangular depending on the photogram dimension. This piramyd isn't an astract element, but rather a pyramid composed by the light rays that coming from the outside into camera through the pinhole, thus the edges of the pyramid that join the pinhole to the photogram vertex being the light rays that define the framing. In the photogram will be exposed all subject inside the piramid edges projected outside until the infinite, thus more bigger will be the largeness of the piramid apex, more bigger will be the framing capability, be deduced that at the same photogram dimension, the framing capability increase when the focal length decrease. This means that at the same photogram dimension, for focal length shorter, will be bigger the pinhole camera capability to made wide angle photograph. Will be intended that, even if the depth of field is infinited, this doesn't means that can appear some blur. The infinite depth of field means that the picture blur doesn't depends by the distance between subject and pinhole, but depends by other issue such as the focal length, the pinhole diameter, the light wave lenght or some subject's movements.

pinhole focal lenght
"Sketch that rappresent the focal length f"

Pinhole diameter

The pinhole diameter is correlated with the focal length. Tehorically, more tiny will be the hole, more the photo shooted will be sharp, but at the same focal length, more being reduced the hole diameter, will be lesser the light volume that come inside the camera with relative increasing of exposure time. Become obvious that exist a relation among the dimension of the pinhole diameter and the focal lenght to obtain sharpned photos. Approximately, to obtain sharpned photos, the pinhole diameter must be 1/100 of the focal length dimension.Auloma wisely vary this ratio to be optimized in its cameras capable to provide photos very sharpnes. In fact, many self made pinhole cameras, own a ratio pinhole/focal length not optimized and suffer about important diffraction effect such as prove their photos that result less clear for the wawing light property. Also the thickness of the material support where is drilled the pinhole is important, a not optimized ratio among the pinhole diametere and support material thikness can be cause of photograms with vignetted border.
The pinhole diameter has a correlation with the focal length. It is available a formula to calculate the right pinhole dimension and was be formulated by Lord Rayleigh at the beginning of XX century. The formula consider the focal length to obtain the pinhole diameter as indicatet here below:

d=1,9 √ f λ

d=Pinhole diameter
f=Focal length
λ=Wavelength of light
λ value for the visible light is a portion of electromagnetic spectre and is included between from 400 until 700 nanometer (nm) (in the air).

Calculate the right dimension is important but also the pinhole geometry become fundamental, the pinhole can't be not perfectly circular and this is possible only if the pinhole is machined by a laser or by special drill bit for high speed spindle.
Auloma cameras use pinhole machined by accurate drill bit for high speed spindle to obtain precise chonical pinhole, because this shape minimize the waving light effect inside the pinhole.

Film plane geometry

In pinhole cameras the film plane could be flat or curved, these two solutions can optimize the film exposure according the focal length. Wide angle pinhole cameras own short focal length, thus as described above, the light that coming inside the camera own a shape like a piramid and in wide angle camera the piramid vertex angle is wide. In this case a flat film plane will be inappropriate because the distance between the photogram edge and the pinhole results too much long respect the rest of the photogram, thus the energy light that arrive onto the edge will be less strong than the center and the final result will be a photogram with blackened corners. Another trouble generated by a flat film plane in a wide angle pinhole camera is the horizon curved, emphatized mainly in panoramic cameras such as in the 6x17 format.

schema pinhole 6x17
"Comparation between a flat and a curved film plane in a pinhole camera 6x17. At the same angle, the same photogram 170mm wide, results illuminated uniformly onto the curved film plane with a ray of 70mm, meanwhile onto the flat film plane the photogram isn't illuminated uniformly, moreover a focal length of 31.6mm need of a pinhole more smaller than the focal lenght of 70mm, this reduces the camera illumination without any benefit about the sharpnes."

Number of pinholes

The presence of one or more pinhole don't change the camera features. Multiples pinholes provide at photographer the possibility to had more possibilities in framing choice with different position of the horizon line, that results positioned at different high in the same frame according the pinhole used for this purpose.

Immage format

The pinhole cameras are dimensioned to use films or photographic papers standard. However exist pinhole cameras developed to use special sizes of photographic papers.The standard formats used are the follows:

  • 135
  • 6x6
  • 6x9
  • 6x12
  • 6x17
  • 4x5"
  • 5x7"
  • 8x10"

Material which is made the camera

Exist many exaple of selfmade pinhole camera obtained by recicled materials such as: cardboard box, beverage can, stove pipe, refrigerator, van and even train. Professional pinhole cameras instead are made mainly with the follow materials:

  • metal sheet used mainly for cameras dedicated for solargraphy
  • Plastic
  • Wood

Exist also pinhole toy cameras made in cardboard, proposed in printed sheet to be cutted and pasted.
Auloma to made its pinhole camera has choose an innovative material, in fact the polyuretane resin added with graphite is an advanced material that provide to Auloma cameras the features necessaries for a professional camera. This choice allows to eliminate all the problems deriving from the use of wood. The final result is a robust pinhole camera, resistant to wet, rain and temperature variation.

Pinhole shutter typology

Pinhole cameras to open and close the pinhole use dirrefent types of shutter actionated by hands. The shutter used mainly in professional pinhol cameras are the follows:

  • By a cork, very efficent system to execute photos that need long exposure time.
  • By linear guide with magnets, all around system suitable for whichever exposure time.
  • By pivoting cover with magnets, all around system suitable for whichever exposure time.

Auloma's pinhole cameras are recognizable for the efficent linar guide system with magnets. The low friction between guides and shutter thanks to the material which are made, joined to the calibrated attraction of the magnets, causes a small force is necessary to open the shutter and avoid camera shake, thus blurred photos in shots that need very short exposure time.

pinhole shutter
"The dowtail deisgn and the low friction makes the Auloma shutter an efficent device with a labyrint that block the light outside the camera when is closed and with a low friction to aid the photographer in fast open close operation without trouble."

How to find your way around the choice

We want just remark that pinhole cameras haven't any electronic devices to manage the shutter opening. To expose the film is necessary the photographer action through its ability opening and closing the shutter for a time calculated previously, see our tutorials or research on internet how to calcuate the exposure time. Aim your choice to companies that provide a schedule with exposure time or something like this, secondly choose a reliable pinhole camera without light leakage. The photos obtained will be available on an analogic support such as film or photographic paper that need of further operations to be fruible. This means that if you want share your work, will be necessary execute operations such as film development, scanning / printing, thus you will be forced to find a film developing shop or equip to yourself and bought all tools necessary for these operations.
For all analogic photograpers beginners, our suggestion is to start with a pinhole camera format 135, this because the film available on the market are less expesive than 120, 4x5 or 8x10 formats and furthermore the tools to developing and scanning this kind of film are not very expensive. This suggestion is valid also for skilled photographers that want start the pinhole experience.

In case you are a wide angle shot lowers or of others photographic effects impposible to be obtained by a digital reflex, your best choice will be a medium format such as 6x12 or 6x17, with the curved film plane. This kind of format need of more expensive investment for film development, printing or scanning, also because 6x12 and 6x17 format often aren't developed from many development shops and you are forced to a DIY (Do It Yourself) solution, that however provide a lot of satisfactions.

Instead if you want obtain the top from pinhole photography the predicted solution will be the large formats 4x5", 5x7" e 8x10". This kind of film formats are more expesive than 135 or 120 and also the tools necessary for developing and printing. However exist a way to test yourself with large format without spend a lot of money, the use of photographic paper can be a good alternative to move the first step because isn't expensive in the post process steps such as developing and printing. In this case aren't necessary any enlargers to print, but is enough develop the photographic paper in the dark room. For this formats are available also snap-shot film, sort of Polaroid®, that don't need any post processing tools and can be a solution convenient and funny in its simple use.