Photographic

Photographic cameras

The camera or camera obscura is the image-forming device, and photographic film or a silicon electronic image sensor is the sensing medium. The respective recording medium can be the film itself, or a digital electronic or magnetic memory.

Photographers control the camera and lens to "expose" the light recording material (such as film) to the required amount of light to form a "latent image" (on film) or "raw file" (in digital cameras) which, after appropriate processing, is converted to a usable image. Modern digital cameras replace film with an electronic image sensor based on light-sensitive electronics such as charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) technology. The resulting digital image is stored electronically, but can be reproduced on paper or film.

The controls usually include but are not limited to the following:
- Focus of the lens
- Aperture of the lens – adjustment of the iris, measured as f-number, which controls the amount of light entering the lens. Aperture also has an effect on focus and depth of field, namely, the smaller the opening [aperture], the less light but the greater the depth of field--that is, the greater the range within which objects appear to be sharply focused.
- Shutter speed – adjustment of the speed (often expressed either as fractions of seconds or as an angle, with mechanical shutters) of the shutter to control the amount of time during which the imaging medium is exposed to light for each exposure. Shutter speed may be used to control the amount of light striking the image plane; 'faster' shutter speeds (that is, those of shorter duration) decrease both the amount of light and the amount of image blurring from subject motion or camera motion.
- White balance – on digital cameras, electronic compensation for the color temperature associated with a given set of lighting conditions, ensuring that white light is registered as such on the imaging chip and therefore that the colors in the frame will appear natural. On mechanical, film-based cameras, this function is served by the operator's choice of film stock. In addition to using white balance to register natural coloration of the image, photographers may employ white balance to aesthetic end, for example white balancing to a blue object in order to obtain a warm color temperature.
- Metering – measurement of exposure at a midtone so that highlights and shadows are exposed according to the photographer's wishes. Many modern cameras feature this ability, though it is traditionally accomplished with the use of a separate light metering device.
- ISO speed – traditionally used to set the film speed of the selected film on film cameras, ISO speeds are employed on modern digital cameras as an indication of the system's gain from light to numerical output and to control the automatic exposure system. A correct combination of ISO speed, aperture, and shutter speed leads to an image that is neither too dark nor too light.
- Auto-focus point – on some cameras, the selection of a point in the imaging frame upon which the auto-focus system will attempt to focus. Many Single-lens reflex cameras (SLR) feature multiple auto-focus points in the viewfinder.

Many other elements of the imaging device itself may have a pronounced effect on the quality and/or aesthetic effect of a given photograph; among them are:
Focal length and type of lens (telephoto or "long" lens, macro, wide angle, fisheye, or zoom)
Filters or scrims placed between the subject and the light recording material, either in front of or behind the lens
Inherent sensitivity of the medium to light intensity and color/wavelengths.
The nature of the light recording material, for example its resolution as measured in pixels or grains of silver halide.

Controlling the photographic exposure and rendering

Camera controls are inter-related. The total amount of light reaching the film plane (the "exposure") changes with the duration of exposure, aperture of the lens, and focal length of the lens (which changes as the lens is zoomed). Changing any of these controls alters the exposure. Many cameras may be set to adjust most or all of these controls automatically. This automatic functionality is useful in many situations, and in most situations to occasional photographers.

The duration of an exposure is referred to as shutter speed, often even in cameras that don't have a physical shutter, and is typically measured in fractions of a second. Aperture is expressed by an f-number or f-stop (derived from focal ratio), which is proportional to the ratio of the focal length to the diameter of the aperture. If the f-number is decreased by a factor of , the aperture diameter is increased by the same factor, and its area is increased by a factor of 2. The f-stops that might be found on a typical lens include 2.8, 4, 5.6, 8, 11, 16, 22, 32, where going up "one stop" (using lower f-stop numbers) doubles the amount of light reaching the film, and stopping down one stop halves the amount of light.

Exposures can be achieved through various combinations of shutter speed and aperture. For example, f/8 at 8 ms (=1/125th of a second) and f/5.6 at 4 ms (=1/250th of a second) yield the same amount of light. The chosen combination has an impact on the final result. In addition to the subject or camera movement that might vary depending on the shutter speed, the aperture (and focal length of the lens) determine the depth of field, which refers to the range of distances from the lens that will be in focus. For example, using a long lens and a large aperture (f/2.8, for example), a subject's eyes might be in sharp focus, but not the tip of the nose. With a smaller aperture (f/22), or a shorter lens, both the subject's eyes and nose can be in focus. With very small apertures, such as pinholes, a wide range of distance can be brought into focus.

Image capture is only part of the image forming process. Regardless of material, some process must be employed to render the latent image captured by the camera into the final photographic work. This process consists of two steps, development, and printing.

During the printing process, modifications can be made to the print by several controls. Many of these controls are similar to controls during image capture, while some are exclusive to the printing process. Most controls have equivalent digital concepts, but some create different effects. For example, dodging and burning controls are different between digital and film processes.

Other printing modifications include:
- Chemicals and process used during film development
- Duration of exposure – equivalent to shutter speed
- Printing aperture – equivalent to aperture, but has no effect on depth of field
- Contrast
- Dodging – reduces exposure of certain print areas, resulting in lighter areas
- Burning – increases exposure of certain areas, resulting in darker areas
- Paper texture – glossy, matte, etc
- Paper type – resin-coated (RC) or fiber-based (FB)
- Paper size
- Toners – used to add warm to cool tones to black and white