In Laboratory on Pinhole Photography we describe the history, the method to take photographs, various pinhole photography, and applications of the pinhole photography. At first, in this page we describe various topics on the pinhole photography in generalities. In the main part of the laboratory these topics are described in more detailed manner. In order to make the description easier to understand we make a point to avoiding mathematical equations and techie expressions. But as in some parts these are necessary, some specialistic themes are described in Appendices. Useful documents and websites are summarized in the page of references.
Pinhole Photography
Pinhole photography is a method to take photographs by a “camera” with a small hole (pinhole) instead of a taking lens. As a light ray goes straight in a vacant space, a light emitted from a surface of an object goes straight through a pinhole and reaches an image screen. Therefore, the end point of the light ray on the screen draws a similar shape of the object as the light emitting points moves on the surface of the object with a fixed point of the ray at the pinhole.
Principle of the Pinhole Photography
A light ray from an object goes straight through a pinhole and draws a shape similar to the object on an image screen.
History of Pinhole Photography
It should be noted that we use terms, “photography” and “photograph” but we don’t intend necessarily to mean by a “photograph” an image recorded on a film or a digital memory of some kinds. We mean an image itself on a screen by the term “photograph” in the pages on the history of the pinhole photography. Since film and photographic printing paper were discovered in the 19th century and a digital camera was discovered in the 20th century, before these days, as a matter of course, images obtained by a pinhole camera were not recorded on these media as a film, printing paper, or an electronic memory.
At the first place, there is a theory that the paleolithic people of more than 10,000 years ago already knew the pinhole phenomenon and they utilized the phenomenon for cave arts and portable arts. This is not a generally accepted theory but as there are no written documents proving such paleolithic pinhole activities it is rather difficult to deny the theory as well as to affirm it. It is very interesting if in future there appear some definitive evidences proving such activities.
The oldest written documents on the pinhole phenomenon are Mo Ti of the 5th century B.C. in China and Problemata Physica by Aristotle of the 4th Century B.C. in the west. In the middle ages optics in the western world as well as other sciences have been developed in Arabic world and transported to Europe in Renaissance. During Renaissance a pinhole camera and a “camera” with a lens instead of a pinhole were called a “camera obscura”, which was used for astronomical observation or painting as a useful devices, and features of the phenomenon were studied extensively. In China, on the other hand, though there were several books on the pinhole phenomenon published after Mo Ti and its features were understood well as in the western world, unfortunately this tradition of the wisdom have not been succeeded to the modern camera technology. This is because the modern science is descended from the western civilization.
As for the history of the pinhole camera in Japan, during Edo period a “camera obscura” was imported from the west and chinese books describing the pinhole phenomenon were transferred from China. Afterward camera obscuras became popular among painters and at present there remain several camera obscuras of that time and a lot of documents describing a camera obscuras. On the pinhole phenomenon itself, however, there are only books by Bakin Takizawa describing the phenomena and a woodblock print of Mt. Fuji projected through a knothole by Hokusai Katsushika. I don’t know if there exists any material on the pinhole phenomenon after them.
Taking Pinhole Photographs
When we take a pinhole photograph we record an image of an object on film, photographic printing paper, or memory of a digital camera. Different from a conventional camera it is an attractive point of a pinhole camera that the camera can be constructed easily in person. If photographic printing paper is used as recording media no complicated take-up device is necessary and, therefore, we can make a large variety of camera bodies by using various empty cans, or wooden or paper boxes. On one hand a silver film camera or a digital camera of a single lens reflex type can be used as a camera body by using a pinhole plate instead of an “interchangeable lens”. This is probably the easiest way to make a pinhole camera. In this site we describe the pinhole photography by using such a single lens reflex (SLR) camera. As for a DIY pinhole camera there are a lot of excellent web sites and it is recommendable to visit such sites. Whichever you use a DIY pinhole camera or a ready-made SLR camera it is very important to make an appropriate pinhole plate for your purpose. It is often employed to paste a pinhole plate made of thin metal foil to a thicker plate with a largish hole because of easiness to make a pinhole of a perfect circle with a designed diameter. At this time it is a question how large is the diameter of the pinhole. It seems that we can get a sharper image with decreasing the diameter of the pinhole, but it is not true. Of course, it is not desirable to decrease the pinhole diameter excessively because a quantity of the light through the pinhole decreases with decreasing the diameter. Moreover, an excessively small diameter is not desirable because the image projected through the too small pinhole blurred by the diffractive phenomenon. As an image by a too large pinhole is of course bleary there must be an optimum diameter size which is not too large nor too small. The optimum diameter (\(d mm\)) is expressed as a function of the focal length (\(f mm\)) as $$d=0.0366\sqrt{f}$$ By using this equation, for example, the optimum diameter of the focal length of 100 mm is calculated as \(d=0.366 mm\). The above equation was obtained for light with the wavelength of 550 nm (1 nm = 0.000001 mm), but in the actual case the wavelength of the visible light ranges from 400 nm to 700 nm, therefore, it is not necessarily meaningful to be too accurate to the above value and a pinhole with the diameter of 0.3 – 0.5 mm will give a considerably good images. Here, it should be remarked that the “focal length of a pinhole” is the “distance from the pinhole to an image screen“. Basically, a pinhole doesn’t converge a light ray to some point and, therefore, it doesn’t have a focus and a focal length, too. 
Focal length and optimum pinhole diameter
To take a sharp pinhole photograph it is necessary to adopt the optimum diameter of a pinhole for the distance from the pinhole to the image screen. Light intensity contours by diffraction are calculated for different pinhole diameters (0.05, 0.15, and 0.3 mm). It is seen that the light diverges abruptly due to diffraction in the case of the small diameter.
Application of Pinhole Photography
Because in a pinhole camera the light intensity at the image screen low and the resolving power is also low in comparison with a conventional camera with a glass lens, it may be difficult to find many practical applications. However as a blurred image makes a special kind of atmosphere, the pinhole photography as an art becomes to enjoy great popularity among photographers. The pinhole photography which many web sites including this site aim at is this kind of the artistic photography.
By the way, in the fields of science and technology the lensless photography (pinhole and zone plate photography) plays an important role to detect and measure invisible light rays (short wave length ultraviolet ray and X ray) and particle rays for which appropriate optical material to be used as a lens is not found. As described above concerning the history, the pinhole photography was used for the astronomical observation in Renaissance and contributed to evolution of the modern sciences. However, as an image by the pinhole camera is very obscure it had limited uses such as for the observation of the sun.
Even at present the pinhole camera is a useful device for amateur astronomers to observe sunspots or solar eclipses. In the case where an object is extremely bright as the sun high resolving power and multiplication can be attained by increasing the focal length sufficiently. For such a purpose even a long focal length as several meters or several tens meters can be realized by making the ray from a pinhole to an image screen horizontal by setting a mirror closely to the pinhole (a pinhole mirror).
More detailed explanation on the pinhole photography is found in the following pages and examples of pinhole photographs which I took by using a film camera and a digital camera are displayed in the Gallery of Pinhole Photographs.