Pinhole Cameras

10 Key excerpts on "Pinhole Cameras"

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  An Introduction to Ray Tracing

  • Andrew S. Glassner(Author)
  • 1989(Publication Date)
  • Morgan Kaufmann

    (Publisher)

  A flat piece of photographic film is placed at the back of a light-proof 2 An Overview of Ray Tracing Pinhole Film Fig. 1. The pinhole camera model. box. A pin is used to pierce a single hole in the front of the box, which is then covered with a piece of opaque tape. When you wish to take a picture, you hold the camera steady and remove the tape for a while. Light will enter the pinhole and strike the film, causing a chemical change in the emulsion. When you're done with the exposure you replace the tape over the hole. Despite its simplicity, this pinhole camera is quite practical for taking real pictures. The pinhole is a necessary part of the camera. If we removed the box and the pinhole and simply exposed the entire sheet of film to the scene, light from all directions would strike all points on the film, saturating the entire surface. We'd get a blank (white) image when we developed this very overexposed film. The pinhole eliminates this problem by allowing only a very small number of light rays to pass from the scene to the film, as shown in Figure 2. In particular, each point on the film can receive light only along the line joining that piece of film and the pinhole. As the pinhole gets bigger, each bit of the film receives more light rays from the world, and the image gets brighter and more blurry. Although more complicated camera models have been used in computer graphics, the pinhole camera model is still popular because of its simplicity and wide range of application. For convenience in programming and Fig. 2. The pinhole only allows particular rays of light to strike the film. Andrew S. Glassner 3 <3 I Eye I Viewing frustum Fig. 3. The modified pinhole camera model as commonly used in computer graphics. modeling, the classic computer graphics version of the pinhole camera moves the plane of the film out in front of the pinhole, and renames the pinhole as the eye, as shown in Figure 3.

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  Light-Matter Interaction

  Fundamentals and Applications

  • John Weiner, P.-T. Ho(Authors)
  • 2008(Publication Date)
  • Wiley-VCH

    (Publisher)

  The pin- hole camera is used in X-ray imaging. The vision of many organisms is afforded by pin-hole ca~neras.~ To illustrate the effects of geometric and wave optics, we will calciilate the size of the pinhole for maximnm spatial resolution. Let the radius of the pin-hole be u and the dist.ance between the hole and the iniage plane d (Fig.8.13a). Light froin the object at a far distance D (>> d ) may be considered as emanating from many points on the object. A point illuniinating the opening will, by geometric optics when u is large, create an image of dimen- sion approximately equal to the pirihole size c1 (Fig. 8.1%). Better resolution, that is, smaller image size of the point, is achieved by reducing the hole. When a is reduced sufficiently, however, according to wave optics, light after passing through the pinhole will diverge, with an angle of about X/(rn); therefore the size of the image is about d . A / ( m ) , which incrcases with decreasing hole size (Fig. 8.13~). The minimum image size is then obtained when the geometric optical iniage size is equal to the wave optical image size, a N d . A / ( T u ) , or d = .rra2/X, the Rayleigh range of the pinhole (Fig. 8.13~1). The same conclusion call be reached using the Fresnel integral, but there is no closed-form solution when the opening is “liard.” When the transmission through the opening is approximated by a Gaussian, a closed form solution can be fomicl and will be treated with Gaussian bearnsas discussed below. Action of a thin lens A lens is “thin” if its thickness is much siiialler than the Rayleigh range as cle- fined by of aperture of the lens, so that in passing through the lens, a beam is not diffracted. The beam, howcver, picks up a phase factor that varies quadratically in the transverse dimension. That phase factor depends on the focal length of the leiis and affects the subsequent diffraction of the beam.

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  Camera Image Quality Benchmarking

  • Jonathan B. Phillips, Henrik Eliasson(Authors)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  The second point implies that there is a contradiction between image brightness and sharpness, since making the hole larger will also mean that light rays originating from one point in the scene will be spread out over a larger area on the back wall of the chamber, thus making the scene blurry. It is therefore necessary to make the hole as small as possible in order to obtain a sharp image. As will be seen later on, this is not entirely true, since optical diffraction will make the image increasingly blurry as the hole diameter is decreased below some limit.

  The third point means that it is possible to shrink the camera obscura down to a more manageable size, which could even be handheld. We then have made what is commonly known as a pinhole camera. This could be said to constitute the archetype of the modern camera.

  While it may seem to be a big leap from the camera obscura to the modern digital camera, the similarities are obvious. In order to overcome the shortcomings of the pinhole camera, a few main functional blocks have evolved. For a digital camera, these blocks can be identified as the lens, image sensor and image signal processor (ISP).

  4.2 Lens

  The tradeoff between image brightness and sharpness of the pinhole camera can in principle be overcome by putting a lens at the position of the pinhole. Rays diverging from a point source in the scene will be collected and focused at the image plane, as shown in Figure 4.2 .

  Figure 4.2

  The principle of the lens. is the focal length.

  4.2.1 Aberrations

  For a perfect lens, all rays emanating from one point in the scene, passing through the lens, will converge at one point in the image. However, in reality this is not the case. Figure 4.3 shows a more realistic lens. Here, parallel light rays coming from infinity are focused by the lens, but not at the same image point along the axis. Clearly, rays farther away from the optical axis (center of the lens in this case) will cross the axis increasingly distant from the position of rays closer to the optical axis. For rays closer to the optical axis, the focus position seems to converge at one point. This is known as the paraxial or Gaussian focus point. Paraxial optics rely on the fact that sines and cosines of small angles can be approximated by the angle and a constant, respectively. For this reason, it is also sometimes referred to as the first-order theory of optics. This simplifies calculations considerably, as, for example, demonstrated in the well-known Gaussian lens formula, relating the object position, , with the image position, , and the focal length,

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  Foundations of Astrophysics

  • Barbara Ryden, Bradley M. Peterson(Authors)
  • 2020(Publication Date)
  • Cambridge University Press

    (Publisher)

  If a permanent record of the projected image is required, an electronic detector or a piece of photographic film can be placed on the wall where the image is located. From Figure 6.2, we see that the image is inverted, and its size is proportional to the length F of the box, called the focal length. Because the pinhole is small, it admits photons at a slow rate. A detector such as a piece of film requires a certain number of photons per unit area to yield a detectable signal; thus, the exposure time t required to produce a detectable image using a pinhole camera can be very long. For a fixed pinhole size, the exposure time is directly proportional to the area of the image; thus, t ∝ F 2 , where F is the focal length of the pinhole camera. Because of 146 6.1 The Telescope as a Camera 147 FIGURE 6.1 A camera obscura, as used to project the image of a nearby church. Object (a) (b) Pinhole Image FIGURE 6.2 A pinhole camera, which is simply a miniature camera obscura. Points on the object, to the left, map onto the image plane on the right. A long camera (a) produces a larger image than a short camera (b). 148 Chapter 6 Astronomical Detection of Light Object Lens Image FIGURE 6.3 By replacing the pinhole in Figure 6.2 with a convex lens, we can admit more light. The image plane is now fixed, and its location depends on the shape of the lens. the relation between focal length and exposure time, a camera with a short focal length is called a fast system, and a camera with a long focal length is called a slow system. In order to reduce exposure times while keeping the image size large, photons must be admitted into the camera at a faster rate. The easiest way to do this is to increase the size of the pinhole. This has the unfortunate consequence of destroying the one-to-one mapping between the object and the image; now many light rays from different parts of the object can reach the same point on the image plane.

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  View Camera Technique

  • Leslie Stroebel(Author)
  • 1999(Publication Date)
  • Routledge

    (Publisher)

  The pinhole can be thought of as transmitting only a single ray of light from each point on the subject, which, since light travels in a straight line in air, can strike only one position on a ground-glass viewing surface or piece of film placed behind the pinhole. The size of the inverted image increases with the distance between the pinhole and the ground glass or film, as shown in Figure 3-1. Instead of a single ray of light, the pinhole actually transmits a very narrow beam of light, one that has the same diameter as the pinhole, from each object point. It would seem logical that the sharpness of the pinhole image would vary inversely with the size of the pinhole, but for a given pinhole-to-film distance there is an optimum pinhole size. If the pinhole is made larger than the optimum size, it transmits too large a beam of light, which reduces image sharpness. If the pinhole is made smaller than the optimum size, it causes the narrow beam to spread out (somewhat like water from the nozzle on a garden hose) due to a phenomenon known as diffraction, which also reduces image sharpness. Figure 3-1 The size of the inverted image formed with a pinhole increases with the pinhole-to-film distance. Images formed by pinholes are not good enough to compete with those formed by photographic lenses, although one may have a moment’s pause in identifying comparison photographs made with a pinhole and a soft-focus portrait lens (Figure 3-2). The image sharpness produced with a pinhole of optimum size used with a 4 × 5-in. or larger film is comparable to that produced with a professional soft-focus portrait lens used at the maximum aperture

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  Optical Imaging and Photography

  Introduction to Science and Technology of Optics, Sensors and Systems

  • Ulrich Teubner, Hans Josef Brückner(Authors)
  • 2019(Publication Date)
  • De Gruyter

    (Publisher)

  That means the projected image is without distortion and we can qualify it as nearly ideal (Figure 2.3). As the imaging is from a 3D-to a 2D space, information about the depth of an object is lost. As a consequence, object points at different distances from the camera located on the same ray across the pinhole will be imaged on the same point in the image plane and can no longer be distinguished. The same type of projection is also applied when 2D images are sketched by an artist, as illustrated in Figure 2.1b. The center of projection in this case is the tip of the rod across which the artist locates the object point and its position in the image frame. y i y a i z object image plane pinhole d u p u d 2 P s i s o D p (c) (a) (b) object camera with pinhole y x z Fig. 2.2: Pinhole camera. (a) Schematic setup. The image is inverted and blurred due to the size of the pinhole; (b) projection characteristics; (c) blur due to diffraction and projection. 58 | 2 Basic concepts of photography and still cameras Fig. 2.3: Pinhole camera photo of a disused railway (author: Joachim K., exposure time 3 minutes¹). The difference from the pinhole camera is that here the object and image spaces are both on the same side relative to the center of projection whereas in the pinhole cam-era the center of projection is in between image and object space and thus separates both spaces. The center of projection in a camera with a lens is the entrance pupil, which is described in more detail in Section 3.4. As for the sharpness of the image in the pinhole camera we have to take into con-sideration two different aspects. First of all, due to the finite aperture D p of the pinhole there can be more than one ray traced from a starting point P in the object space to the image plane. Consequently this is not an unambiguous point-to-point imaging pro-cess and implies that we get a blurred spot on the image plane with a diameter u p (see Figure 2.2c).

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  The Limits of Resolution

  • Geoffrey de Villiers, E. Roy Pike(Authors)
  • 2016(Publication Date)
  • CRC Press

    (Publisher)

  Petzval [ 42 , 43 ] was the first to attempt to determine the optimal pinhole size. Rayleigh [ 44 ] improved on his results and showed, using Huygens–Fresnel diffraction, that the best results are obtained when the aperture, as seen from the image plane, has a diameter of 0.9 times that of the first Fresnel zone. To be more precise, if r is the radius of the aperture, then r 2 a + b ab = 0.9 λ , where λ is the wavelength of the radiation a is the distance of the object to the pinhole b is the distance of the pinhole from the image plane The pinhole camera is discussed in more modern times by, for example, Hardy and Perrin [ 45 ], Wood [ 46 ], Goodman [ 47 ] and Sharma [ 48 ]. Early Concepts of Resolution 11 FIGURE 1.5: Photograph taken with a camera obscura at King’s College London. Figure 1.5 is a photograph taken with a camera obscura at King’s College London ∗ . The view is over the south bank of the River Thames. The scene was sunlit and an aperture of 5 mm diameter was used with a white image screen at 1 m distance. With less daylight, acceptable pictures could still be obtained with lensless apertures as large as 1 cm. 1.1.4 Coherent and Incoherent Imaging In this section, we look at two fundamental forms of optical imaging, namely, coherent and incoherent imaging. Coherent imaging involves light from all parts of the illuminated object having the same phase relationships as time varies. In other words, the phase differences between parts of the object are independent of time. A typical scenario would be a semi-transparent object illuminated from behind by laser light. The amplitude and phase of the light would vary across the object but these variations would be constant in time. We will make the assumption when talking about coherent imaging that the detector responds linearly to the amplitude of the received waveform, rather than the intensity. This can be accomplished by optical homodyning or heterodyning.

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  Experimental Filmmaking

  BREAK THE MACHINE

  • Kathryn Ramey(Author)
  • 2015(Publication Date)
  • Routledge

    (Publisher)

  CHAPTER 10 Pinhole Photography Film/video/digital The etymology of the word camera comes from both the Latin word for chamber (a fancy word for a room) and the Greek word for a covered enclosure. A camera obscura (Latin for “dark room”) was an optical device used for scientific investigation, entertainment and as an aid in drawing for over 2000 years. The basic mechanics of a camera obscura are a “dark chamber” with a very small opening (aperture) to a well-lit area beyond and it is possible to make one out of any room or box providing you can get it dark enough. If you created an entirely dark chamber with just a small opening to the outside, what you would see opposite that opening would be an upside-down image of the outside world. The science behind this is rather ancient. Light travels in straight lines. This much was observed by a Chinese philosopher named Mo-Ti around 400 BCE. There were many other artists, philosophers and scientists whose fields of interest engaged with optics and light, and who used different kinds of optical devices in their research and work contributing significantly to the formulation of the camera obscura. The first accurate description of the science behind the device as well as how vision works can be seen in the writings of Abū ‘Alī al-Ḥasan ibn al-Haytham, born in Basra, Iraq, working out of Cairo, Egypt, in the 10th century CE and known in the Latin-speaking world as Alhazen. His work came to Europe via a 13th-century Latin translation and it is credited with revolutionizing medieval understandings of mathematics, optics and light. Leonardo da Vinci (1452–1519) described the use of a camera obscura device as an aid in drawing in his Codex Atlanticus and artist Giovanni Battista della Porta (1538–1615) added a lens to the aperture (opening) on the box in order to focus the rays of light and make the image brighter. All that remained for the invention of photography was the discovery of a substance sensitive to light (e.g

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  The Book of Alternative Photographic Processes

  • Christopher James(Author)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. THE BOOK OF ALTERNATIVE PHOTOGRAPHIC PROCESSES THIRD EDITION 10 With the advent of the telescope and the ability to craft and work glass into tools of magnification, scientists placed multiple, and differently shaped, lenses on their small camera obscura holes. They then noticed that, depending on the distance between the aperture hole and the plane where the image landed (the image distance), they could focus and alter the effects of the image. In 1604, mathematician and father of modern optics Johannes Kepler (1571–1630) worked out a formal rela-tionship between mirrors, lenses, and vision. Five years later, in 1609, Kepler wrote a book titled Astronomia nova that had a profound influence on the way scientists thought about light; he was the first to describe the “ray theory of light” to explain vision and what our eyes are able to see. One of the strongest reactions to Kepler’s work was seen in the writings of Isaac Newton (1643–1727), who in 1675 demonstrated with a prism that white light wasn’t really white at all—it was actu-ally an entire spectrum of colors. Kepler, by the way, is credited with being the first to use the words “camera obscura” together to describe the instrument. The evolution of these early cameras, which worked nicely as drawing aids for painters, is fairly well docu-mented. But for the advent of photography itself, some chemical discoveries also had to happen. In 1725, Figure 1–8 Eric Renner & Nancy Spencer, Evolushin, “on deaf ears” series, 2001–2006 (Type C pinhole from 4 × 5 negative) The pinhole images in on deaf ears are the result of a collaboration between Eric Renner and Nancy Spencer, . . . the operators of Pinhole Resource. Sixteen years ago they began constructing assemblages, many of which dealt with social issues of human rights, religion, sexuality, and stereotypes.

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  Pinhole Photography

  From Historic Technique to Digital Application

  • Eric Renner(Author)
  • 2012(Publication Date)
  • Routledge

    (Publisher)

  CHAPTER 6

  The Advanced How-To of Pinhole Photography

  Learning without thought is useless. Thought without learning is dangerous. Confucius, 500 B.C.

  Can scenarios of perception be created with the pinhole camera that were not anticipated by nature?

  Hans Knuchel, Camera Obscura , 1992

  OPTIMAL PINHOLE FORMULAS

  Useful information:

  •  Light intensity decreases the further it travels from the pinhole . For instance, a 4-inch focal distance takes more time to expose than a 3-inch focal distance when the optimal pinhole is used.

  •  As the focal distance increases, the optimal pinhole increases in diameter . For every focal length, there is an optimal pinhole diameter. Robert Mikrut and Kenneth A. Connors developed a chart of focal distances and corresponding optimal pinholes (Figure 6.1A ). Needle shaft diameters are shown in Figure 6.1B . An example of an optimally sharp pinhole image can be seen in Figure 1.34 . If the pinhole is too large for the focal length, the image will be blurry. If the pinhole is very, very small, the image will also be faint and blurry because light cannot enter the pinhole properly without destroying itself.

  Figure 6.1A © Robert Mikrut and Kenneth A. Connors, pinhole calculations from 10- to 1000-mm focal lengths.

  Figure 6.1B Needle shaft diameters.

  The Time-Rel. to f/64 column in the chart is useful if you have a light meter that only reads as high as f /64 and you are using an optimal pinhole of a specified focal length and known f /stop. You would set your meter to your film speed and read the exposure time for f /64 related to your optimal pinhole focal length and then multiply that time by the numbers on the chart’s Time-Rel. to f/64 column. For instance, if you had a focal length of 150 mm (6 inches) using an optimal pinhole of 0.4532 mm, you would read your light meter’s exposure time for f /64 and multiply it by 5.91. That would be your exposure time for an f /stop of 331.

  A formula can be derived for making pinholes of the correct size. Any number of slightly differing formulas have been calculated since Lord Rayleigh calculated his in the 1880s. The one shown here is by Bob Dome of Washington State. It is derived from Rayleigh’s formula, as well as from Mikrut and Connors’:

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