Pinhole basics

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Pinhole photography attracts with simplicity and slow speed of image making (a digital camera conversion would give the instant gratification factor, which hopefully will have never become a norm). However, one would be ill advised thinking pinhole cameras are little more than a box with a hole and a sensitized medium behind it.

Pinhole gives photographer some notable advantages over lens based imagery:

  • large freedom for experimentation and expression
  • wide range of image forming devices (cameras) with nearly infinite possibilities
  • ease of use of any sensitized material
  • extremely low cost of getting started (although this can grow into a yet another expensive hobby)
  • relative unpredictability of results (if one chooses so)
  • while camera design can get quite involved, it is still a simple instrument where few things can stop functioning, making it robust and dependable
Forth Railway Bridge, Edinburgh, Scotland

Forth Railway Bridge, Edinburgh, Scotland

There are however obvious drawbacks as well:

  • depending on expectations, not everyone will find results worthwhile (especially those who decide not to study the principles involved)
  • unpredictability of results (if one chooses so), but this can mostly be controlled quite well
  • slow and extremely slow exposure times do not fit well a lot of subjects

A few basic concepts of pinhole photography:

  1. image is formed by a small hole (pinhole) placed in front of a sensitized material, the hole acts as a light ray “eliminator” thus allowing each point of a scene to be projected onto camera back with surprisingly good resolution (partly dependent on camera design and construction)
  2. images have an inherent extremely deep depth of field, which can be further enhanced by specific camera design for closely positioned subjects (an article in its own right)
  3. image quality (sharpness and contrast) depends on several factors, most controllable by camera designer/maker,  the most critical component being the quality of the pinhole and its size
  4. due to light allowed through the hole being considerably less than in lens based photography, very long exposure times are required, this can either eliminate some areas of interest or can be used to advantage, possibilities are practically endless
Grangemouth, Scotland

Grangemouth, Scotland

There are few design factors one should remember, especially if best possible image cross illumination and sharpness is the goal:

  • there is a proven correlation between image’s perceived sharpness and pinhole size relative to its distance from film plane
  • the often referred to “focal length” of a pinhole camera is simply the distance from film plane to the hole, image sharpness extends from about 10-20 times of this distance to infinity, it is possible to design a pinhole camera for macro work, which will allow for improved sharpness of subject much closer to the pinhole (this concept is mostly overlooked or ignored in pinhole discussions)
  • film plane can be flat or curved and perpendicular or angled to the optical axis, each having its own curiosity factor and problems
  • pinhole itself, while generally needing to be as round as possible, can have other shapes which may or may not be advantageous
  • curved film plane makes more even exposure (especially in panoramic images), but introduces horizontal line(s) curvature which may offset illumination advantages
  • maximum angle of coverage (AoC)of a pinhole largely depends on the thickness of the material in which it is made and diameter of hole
  • angle of view (AoV) of the camera is a function of film size and its distance to the hole, so long as AoV is smaller than AoC, image vignetting effect will be limited to almost non existent
  • camera f-stop is a function of film to hole distance (FHD) divided by hole diameter (HD), this typically turns out to be well above 128 value (typically in 300 range) which introduces some difficulty in exposure prediction
  • exposure compensation involves not only  multiplication of metered value to match actual f-stop of the camera (there are no light meters extending to pinhole camera f-stops), but also reciprocity failure effect must be accounted for, the latter however is dependent on the sensitized material used and may require testing for improved exposure prediction
Falkirk, Scotland

Falkirk, Scotland

One of the signature features of many pinhole images is vignetting evident in image darkening at the borders and corners. With careful camera design this can be largely avoided, if one desires such an effect. In fact, while pinhole cannot match lens derived image sharpness or contrast, it can deliver surprising resolving quality while giving (arguably) extremely attractive moody depth a lens cannot achieve.

Pinhole images often show as blurry, dirty, distorted, badly exposed variety (causing many viewers to believe they are witnessing pinhole capabilities). Many accept them as “arty” and seem to argue this is indeed how things are suppose to be. The fact is that in majority of such cases, photographer had little clue of the process and the made image was a result of accidental turn of events rather than a controlled process.  Pinhole image can in fact be quite sharp, fairly evenly (and properly) exposed, and with its inherent near infinite depth of field and softness can often compete with a lens photograph for overall appeal.


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