The word 'photography' made of two Greek root words 'photo' and 'graph'. Photo means light and graph means drawing and together means "drawing with light." Capturing light using camera is a technology but conveying a message via captured light is an art. Photographers (invariably from non-science background) use the camera to take stunning visuals. The science behind the photographic technology is called optics. Optical scientists and photographers are two sides of same coin. Both of them explain their side very beautifully. A unified view if provided will help the general public to grasp both sides easily.
Camera captures the reflected light from the subject (human being, animal or object of interest). The light may have originated from Sun or artificial light source. The reflected light is channelized via opaque diaphragm with an aperture (a small hole). Present day digital camera with aid of lens, (actually multi-lens arrangement) makes the light to fall on to the two-dimensional array of light sensors. The sensor may be made up of CMOS and CCD technology. Light sensors convert the light into electrical signals and given to Analog-to-Digital converters to provide digital output. This raw digital data is compressed and stored as JPEG image file. The JPEG file can be viewed on a screen present in the camera or can be transferred to computer for further processing.
Optics is a branch of physics that deals with the interaction between light and matter. Light exhibits dual nature. Sometimes it behaves like a wave and other times as a particle. Light is a small portion in electromagnetic spectrum having a wavelength ranging from 400 nanometer to 700 nm. The optics can be broadly classified as geometric optics, physical optics and quantum optics. In school days geometric optics is taught as it is the simplest model to explain the interaction between light and matter. It introduces optical ray and discusses mechanisms like reflection, absorption and refraction. Phenomenon like photoelectric effect can be explained using photons (particle form of light). Quantum optics deals with photons in detail. In geometrical optics, we study about lens (concave and convex) and image formation. Knowledge in geometric optics is sufficient to understand the mechanism of light capture. To know the functioning of sensors and A-to-D converters knowledge on electronics and photonics is necessary. School books seldom deal with application of geometric optics in photography.
A simplified anatomy of eye will be presented and compared with camera in school science book as well as in digital image processing books. It is a case of over simplification. This notion forms a great barrier to understand, human perceive images rather than see images. There is a close coordination between eye and brain in construction of image and understanding the image. Human Iris will dilate itself to allow more light to pass via pupil (black in colour in the centre of the eye) in night. But change will be minimal. In cat opening of pupil will be distinct. In the night cat pupil will be large and in noon it will be like a vertical slit. Size of pupil opening is varied to control the light falls on the retina.
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| Figure 1. Cat pupil in the shape of vertical slit Courtesy: Krysten Merriman [1] |
For a photographer camera is just a tool to accomplish their goals. They have to select the subject with accompanying objects from scenery and make sure that desired light that falls on the film or sensor to make stunning visuals. The term 'exposure' is used to describe the amount of light falls on the film. The exposure is a function of luminance of the subject and duration. Photographers control the size of the aperture and duration of opening to make beautiful photos. So, entire description of taking photos will rely on three things aperture, shutter speed and ISO. The sensitivity of film to light or sensor is described using ISO. The aperture of diaphragm closely resembles cat's pupil (any analogy take with pinch of salt).
Students of optics and photography enthusiast follow different approaches to describe 'light capture'. A simplified unified view is not readily available to us. But constructing a one may not be difficult as it requires basic knowledge in geometric optics and ability to find and read good photography tutorials in Internet.
[1] Free stock photo of animal, cat, adorable, https://www.pexels.com/photo/cat-whiskers-kitty-tabby-20787/
