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A Thorough Glossary of Digital Photography Terminology
This is a reference of useful digital photography terminology, all of which pops up in various sections of Photography Art Cafe. This page will be continually added to, so over time will become a really useful resource for you to look up an unfamiliar term, or re-cap on some basic concepts and definitions.
AE-L: "Auto Exposure Lock", a feature that locks in the exposure settings when shooting in automatic or semi-automatic modes. When this button is pressed, the light meter will not take a new reading when the camera is pointed in a different direction. Useful when used with the focus-and-recompose method.
Ambient light: Natural or artifical light surrounding a subject that is already present in the scene, i.e. light not supplied by the photographer's equipment.
Angle of View: The scope of a scene covered by a given lens. Angle of view is determined by focal length. So a wide angle lens has a large angle of view, whilst a telephoto lens has a small angle of view.
Aperture: The hole in a lens that admits light into the camera to form an image. It is formed by an iris of interlocking blades that can be adjusted to change the size of the hole. The smaller the aperture, the larger the depth of field and vice versa. Aperture size is measured in f stops and, together with shutter speed and ISO, it forms part of the exposure triangle.
Aperture (Software): Image managing and processing software designed by Apple, that provides a single platform for organizing and editing images. Aperture enables non-destructive image editing.
Aperture Priority: A semi-automatic exposure mode which provides the photographer full control of the aperture, whilst the shutter speed is selected by the camera to produce an accurate exposure.
Autofocus: The system by which a lens automatically focuses on a selected part of a scene. Different autofocus points can be used, as well as the ability to continually re-focus to track a moving subject.
Bit Depth: The colour range of digital photo file. An 8 bit image offers 8 bits of colour per colour channel (red, green and blue), which is 24 bits per pixel. A 16 bit image offers 16 bits per colour channel, or 48 bits per pixel. The larger the bit depth the more freedom you have in post-processing to adjust colours without posterization occuring. Raw files have considerably greater bit depth than JPEG files.
Bracketing: The manual or automatic process of taking several images of the same subject with different exposure settings. When this is automated it is called 'automatic exposure bracketing (AEB). The purpose of bracketing is either to a) blend multiple exposures to create an image of high dynamic range or b) give yourself the opportunity to choose the best exposure of a scene with tricky lighting.
Bridge Camera: A type of camera that is intended to bridge the gap between compacts and DSLR's. They feature image sensors that are larger than compacts but smaller than DSLR's. Most bridge cameras also have a zoom lens with a high level of magnification. They are small and portable, produce good quality images and tend use up battery life fast.
Brightness: The intensity of light measured by the camera's light meter.
Bulb Mode: A shutter speed setting ('B') where the shutter remains open for as long as the shutter release button is pressed. This allows for extremely long exposures.
Camera Obscura: A large scale, simply designed camera that functions like a pinhole camera. Light is admitted through a tiny hole in a wall of a light-proof room and falls on to a plain surface at the back of the room, forming an image.
Camera Shake: The slight movement of the camera when holding it in your hands to take a picture. Camera shake inevitably causes blur, unless a sufficiently fast shutter speed is selected (usually a minimum of about 1/50th is required).
CMYK: The colour spaced used by digital photo printers. CMYK stands for cyan, magenta yellow and (key) black, the 4 basic colours used to render digital images as prints. Different versions of these 4 colours are available (e.g. light magenta), with higher end printers offering a greater number of variants, in turn producing higher quality prints. The CMYK colour space is not able to produce as wide a range of colours as the RGB colour space, used by digital cameras and computers.
Crop Factor: Cameras with an image sensor the same size as a frame of 35mm film are called 'full frame'. Beginner and prosumer level DSLR's use smaller sensors, which effectively 'crop' images, increasing the level of magnification. The image projected by the lens cannot be contained within a smaller sensor (unlike a full frame sensor, where it would show fully), so the the edges are cropped out. The extent to which this cropping (and effective increase of focal length / magnification) occurs is called crop factor. Most non full-frame sensors have a crop factor in the region of 1.5x. In other words, focal length is 1.5x that stated on the lens.
Compact Camera: The simplest type of popular digital camera available. Compacts, or point-and-shoots, are portable, contain small sensors, feature a Live View LCD screen, offer a certain amount of magnification and usually afford some manual control over exposure settings.
Depth of field: The area either side of the focal point that is in acceptably sharp focus. Small apertures produce a large depth of field and vice versa.
Diffraction: An effect created by light beams entering the aperture of a lens and coming into contact with the edge of the iris, which leads to blur. Diffraction becomes noticeable at small apertures (high f numbers), because a higher proportion of the light entering the camera has contacted the edge of the iris blades. So diffraction undermines the sharpness that accompanies very large depths of fields, often making the use of extremely high f numbers counter-productive.
DSLR: Digital single lens reflex (DSLR) cameras are the largest, most expensive and highest performing digital camera type. They contain large sensors capable of producing brilliant images, are less prone to noise (graininess) in low light conditions, use interchangeable lenses and offer extensive control of all settings.
Exposure: The amount of light allowed to enter a camera resulting from the aperture, shutter speed settings. The more light, the brighter the image and the less light, the darker the image. 'Exposure' also sometimes refers to an image itself.
Exposure Value: A measurement of the brightness of light in a given scene. Each increase on the EV scale amounts to a doubling of brightness.
Exposure Time: The duration of time for which the image sensor (or film) is exposed to light entering through the camera. Exposure time is determined by shutter speed.
Exposure Compensation: A control for increasing/decreasing the exposure of an image, measured in stops and 1/3 stops, whilst in an automatic or semi-automatic mode. The camera automatically adjusts shutter speed and/or aperture to produce a darker/brighter image. This is very useful when the light meter is struggling to produce a suitable reading in difficult light.
Exposure Bracketing: (See "bracketing")
Exposure Mode: Also referred to as "shooting mode", the camera mode used used to select the exposure settings for an image. Different exposure modes afford various levels of control over aperture and shutter speed. Manual mode offers full control of both, whilst aperture priority and shutter priority are "semi automatic", with program mode the fully automatic option.
Exposure Triangle: The 3 key controls used for determining the exposure of a photo, namely: aperture, shutter speed and ISO. These controls are interconnected and have a reciprocal relationship.
File Format: The file type saving digital photograph in the memory card, or for storage on the computer. JPEG, Raw and sometimes TIFF are the options for saving images to a card. Meanwhile there are several file format options, each for different purposes, when it comes to saving images on the computer (e.g. JPEG, PNG, TIFF, Photoshop PDF, Photoshop PSD).
Flash: Electronic flash in digital cameras is a battery powered light that fires during an exposure to supply an artificial light source where there is inadequate ambient light. Compact cameras usually have a built-in flash, whilst DSLR's feature a pop-up flash. Both of those options yield hard, direct and unflattering light. Using an external flash unit (speedlight) enables the photographer to produce angled, bounced, diffused light, which is much softer and more naturalistic.
Flash compensation: A control in digital cameras for reducing the output of flash. This gives the photographer additional control for lighting a scene correctly
Fast Lens: A lens with a wide maximum aperture, compared to others in its category. The wide aperture makes possible faster shutter speeds, enabling good pictures to be taken in low light.
Focal Length: The distance required for a lens to focus light that enters parallel to it. This is influenced by the shape of the surface of the lens (the more bent, the shorter the focal length) and the refractive quality of the material (the capacity of the material to bend light). The longer the focal length the greater the magnification and smaller the angle of view.
F stop/number: A number corresponding to the width of the aperture. Each increase in f stop doubles the size of the aperture, and each decrease halves it. Aperture settings in digital cameras are not simply organized on a scale of whole exposure stops. Rather, we can adjust the aperture by 1/3 stops at a time.
Full frame: A digital image sensor the same size as a frame of 35mm film. Full frame cameras are the most expensive, produce outstanding quality images, are capable of extreme low light shooting (whilst maintaining noise free quality) and do not have a crop factor.
Fill flash: A method of using flash to fill in the foreground of an image, whilst still capturing the background ambient light. For example, outdoor portraits often make use of fill flash, enabling the photographer to expose for the nackground light without also underexposing the subject.
Filters: Filters apply certain effects to images when attached to the end of a lens. Filters have, in large part, been replaced by the range of digital post-production effects that can be applied. But three types remain invaluable, especially for the landscape photographer: neutral density, neutral density graduated and polarizing. UV filters are also popular as a means to protect lenses.
Graininess: (See "noise" and "ISO")
Histogram: A graph representing the range and intensity of tones in a photograph. The histogram can be viewed in-camera or in post-production. It is an invaluable way of assessing the exposure of an image and checking for over/underexposed areas.
Hot Shoe: The attachment on a DSLR, usually above the viewfinder, for placing an external flash unit.
ISO: ISO speed is a measurement of how fast a digital image sensor can record light to form an image. Increasing ISO effectively amplifies the light within the sensor, but latent electronic current (noise) is also amplified. So when an exposure is made with a high ISO setting, noise (graininess) is more prevalent. Photographers usually choose to shoot at the lowest ISO setting by default.
Image sensor: The image sensor in digital cameras records light and converts it into electric current, which is saved in the memory card. The large the sensor, the larger the photosensors on its surface, which in turn leads to better image quality and improved low light performance. Image sensors vary in size, the largest being full frame (equivalent to a frame of 35mm film).
Kelvin: A measure of the colour of light, based upon the degrees Kelvin temperature scale. Counter-intuitively, lower temperatures on the scale are warm red/orange tone, whilst higher temperatures ar a cool blue tone.
Lens Speed: (See "Fast Lens")
Lightroom: Image managing and editing software created by Adobe. Lightroom provides a simple platform for organising images and editing them non-destructively.
Light Meter: The device that measures the brightness of light in a scene. The light meter can be controlled to read light from the entire scene, and average it out, or from more precise areas. The light meter sends its information to the exposure meter display, which enables us to select appropriate exposure settings.
Maximum Aperture: The largest available aperture setting for a given lens. The maximum aperture is an important specification of a lens because it determines lens speed and impacts the visual character of out-of-focus areas (bokeh).
Magnification: The amout a scene is magnified by a lens. The focal length of the lens determines magnification. The higher the focal length, the greater the magnification and the smaller the angle of view. Increasing focal length to increase magnification is not to be confused with cropping, the latter producing a magnified effect, but also reducing the number of pixels in an image. So called 'digital zoom' in compact cameras is nothing more than cropping, whilst 'optical zoom' in compacts is genuine magnification.
Metering Mode: The mode used for measuring light with the light meter. These modes enable us to specify the area in a scene from which light is read. Evaluative/matrix metering assesses light from the entire scene and averages it out. Centre weighted metering either takes light from the central area of the frame, or takes light from the entire scene but weights that from the centre more heavily (depending on your camera manufacturer). Spot metering is the most accurate metering mode, reading only light from the very centre.
Mirrorless Camera: A camera type that is similar in size, design and usability to compact cameras, but uses large image sensors and interchangeable lenses like DSLR's.
Noise: A grainy texture that appears in photos taken with high ISO settings. Noise is also more prevalent in the blue colour channel. Full frame sensors are much less prone to noise than their crop factor counterparts. All image sensors have a certain amount of latent electronic current (a constant hum of current). Usually the information provided by light entering through the lens (the 'signal'), which is also converted into electronic current, is so strong it drowns this out. But at high ISO speeds, the 'gain' of the sensor (its ability to record light) is amplified, which also increases the latent current, or noise. So, for a correctly exposed photo taken with high ISO, the noise level will be higher.
Photoshop: Post-processing software created by Adobe. The full version of Photoshop (CS) provides extensive editing features for keen amateurs of professionals. A cheaper, simplified version is available called Photoshop Elements. Photoshop can be used in conjunction with Adobe Bridge, an image managing/organizing application.
Prime Lens: A lens with a fixed focal length, e.g. 35mm, 50mm or 80mm. Fast prime lenses can be purchased more cheaply than fast zoom lenses. Plus, they tend to yield clearer images, thanks to the presence of less moving parts.
RGB: A colour space made up of three primary colours (red, green and blue) used by all devices that represent colour with light. Digital cameras use RGB, with 3 main variants: sRGB, Adobe RGB (1998) and ProPhoto RGB. Post-production software also works in RGB colour space. The red, green and blue colours are referred to as colour channels. The bit depth of a photo is measured in terms of the range of different versions of red, green and blue available.
Reflex mirror: The mirror in DSLR's that reflects the light entering through the lens at a 45 degree angle up to the viewfinder, allowing the photographer to see the scene. When the shutter release is pressed, the reflex mirror flips up to expose the sensor. The mirror can be locked-up temporarily to a) reduce camera shake that can result from its movement b) clean the image sensor.
Shutter Speed: One of the points on the exposure triangle that is used for determining the brightness of a picture. Shutter speed is a control that sets the speed at which the shutter (comprised of 2 "curtains") moves. The shutter speed is measured in seconds and translates as the length of time for which the image sensor will be exposed (e.g. 1/200th of a second, or 1/15th of a second). Fast shutter speeds freeze motion, whilst slow shutter speeds (requiring a tripod) capture the path of motion.
Shutter Lag: The slight delay that occurs between the moment the shutter release is pressed and when the exposure actually takes place. The mechanism of the shutter does not respond absolutely instantaneously, requiring a certain amount of anticipation on the part of the photographer when shooting fast moving subjects.
Sensor: (See "Image Sensor")
Stop: A measurement of a change in the exposure of a photo. An increase of 1 stop of exposure amounts to a doubling in brightness, whilst a decrease of 1 stop is a halving of brightness.
Sharpness: A rather subjective concept, that basically refers to the sharpness/crispness of the edges in a photo. Sharpness can be achieved in-camera by using a sufficiently fast shutter speed to avoid camera shake, accurate focusing and use of a lens' optimum aperture. The direction and quality of light also influences the sharpness, or "pop", of an image. Sharpness can be applied subtly to edges in post-production software.
Vignetting: A reduction of light around the corners of an image. Vignetting is usually caused by lenses. All lenses produce images that are slightly darker at the edges than in the centre, because the light has further to travel from the edges of the lens to the centre of the frame, so falls away more. Some lenses are more prone to it than others, especially wide angle lenses. An oversized or ill-fitting lens hood, as well as multiple stacked filters can also lead to vignetting.
Vignetting can sometimes be used intentionally (in post-production) as a creative framing technique, drawing attention to the subject in the centre of the frame. But this often looks quite dated and crude, unless done really subtly. Unwanted vignetting can also be removed in post-production.
White Balance: The control of colour balance in photographs. A colour cast can be thrown over an image to compensate for the temperature of a light source and create a naturalistic image. White balance can be set using in-camera pre-set options, or in conversion software if the image is a Raw file.
Zoom Lens: A lens with variable focal length, as opposed to a prime lens which has a fixed focal length. Zoom lenses have the advantage of flexibility whilst shooting. But the optics of zoom lenses is more complex than primes, resulting in slightly less clear images. Zoom lenses also a typically not as fast as most prime lenses.
If there are any other useful terms you'd like to see in this glossary of digital photography terminology, please drop me a line or leave a suggestion in the comments. I hope this helped you find what you were looking for!