Glossary of SLR Cameras Terms
A self-cleaning system that clears the sensors surface of microscopic dust particles that may have settled on the sensor during a lens change. This is generally achieved through the use of high frequency vibration.
Aperture / Iris
An adjustable opening. Light enters the camera, passes through the lens and aperture / iris and then falls onto the light sensor at the back of the lens. This is one of the principal controls used in exposure control (see below). See also aperture control below.
A setting that controls the amount of light entering the camera. It is measured in f-stops. The lower the f-stop, the larger the aperture, so the more light enters the camera, resulting in a lighter / stronger exposure.
Almost all digital cameras come with this feature. The camera automatically focuses on the subject at the centre of the image using motorised adjustment of the lens' focal length.
Enables a burst of images all with the same settings, to be captured in rapid succession by depressing and holding down the shutter button. The number of images captured per second varies between camera model. Some photographers also refer to this as bracketing.
CCD Image Sensor (Charged Coupled Device)
When the light hits this sensor whilst taking a photo, the CCD sensor converts the image information to digital data for storage. This is the principal sensor technology in use in most consumer digital cameras.
CMOS Image Sensor (Complementary Metal Oxide Semiconductor)
A light sensitive semiconductor sensor in a digital SLR camera that incorporates an amplifier matched to each of its pixels. CMOS is a direct alternative to CCD (see above). The individual amplifiers attached to the CMOS sensor can help in reducing heat which can otherwise cause noise in the resulting image. The CMOS sensor converts the image information into digital form for storage.
A software process in a digital SLR camera whereby the centre of an image is digitally enlarged. Since digital zoom requires software manipulation of the image within the camera, image quality is reduced significantly when compared to optical zoom (see below) but it allows for magnification many times that of its optical counterpart. Many digital SLR cameras incorporate both zoom technologies.
This allows you to explicitly adjust the camera's settings including aperture and shutter speed to compensate for certain adverse lighting conditions. Many modern cameras incorporate automatic exposure compensation but there will inevitably be times when you need to override this.
A selection of modes to choose from, typically including Manual, Aperture Priority, Shutter Priority, and Picture Modes. Each of these is suited to different shooting conditions and will adjust the camera's settings accordingly. For example, Shutter Priority model will allow you to manually set perhaps a fast shutter speed (see below) to take an action shot, and will adjust the f-stop and other settings to optimise the shot accordingly.
Some SLR cameras incorporate a built in flash, but these tend to have less power than an external flash. The internal flash unit will also consume power from the camera's main batteries and is thus regarded by many as being a backup rather than the primary flash. External flashes are generally attached to an SLR camera by means of a bayonet type fixture at the top of the camera's body. Depending on the camera and flash chosen, there may be a great deal of automatic synchronisation and control between the two devices.
Measured in millimetres, the focal length stated for a lens is the lens' focal length when set to infinity. The rear of the lens is separated from the camera's film or image sensor by the focal length. For zoom lenses the focal length will be quoted as a range, for example 28-80mm. 28mm is regarded as a wide angle lens. 35mm is the 'staple' of the SLR word, being a good general purpose lens. Almost all SLR cameras will allow interchangeable lenses, many coming with more than one lens.
Frames / second
The maximum number of shots per second. Higher numbers here mean quicker continuous shooting which is important if you intend to capture sporting action or fast moving wild life, for example.
Most modern SLR cameras come with auto focus (see above). Some will allow a manual focus mode for capturing shots where the subject focus differs from the camera's auto focus default. Other common options include 'continuous AF' mode for action shots or a 'one shot' mode wherein the camera focuses on the scene viewed through the viewfinder and 'snapshots' or fixes the focus when you half depress the shutter button and then holds that focus until you fully press down the shutter release button to take the shot. Here, if your subject moves, the camera will not refocus.
A feature found in many digital SLR cameras that compensates for camera shake when the camera is hand held, resulting in relatively blur free shots. Some more expensive models may offer optical stabilisation using miniature gyroscopes to stabilise the lens assembly. This has the advantage of avoiding digital manipulation of the image which can sometimes affect image quality.
Many SLR cameras allow you to change lenses to suit the shot. Examples include close ups, or zooming in. The range of lenses available varies between camera models and manufacturers although there are many generic lens manufacturers.
The ISO number denotes how sensitive the image sensor or film is to the incoming light. The higher the ISO rating, the more sensitive the film (or sensor) will be to exposure. 100 ISO is a common general purpose value. ISO is fixed for film but the sensors can be adjusted on many digital SLRs and will affect the camera's receptiveness to light. Settings ascend in a common scale on nearly all SLR digital cameras as follows: 50 – 100 – 200 – 400 – 800 – 1600 – 3200
A compressed image file format, allowing storage of a greater number of images onto digital storage media. JPEG files are widely supported in computer graphics applications and for upload to the internet.
A LCD (Liquid Crystal Display) screen is common on many modern SLRs. This is typically where the menu can be viewed and settings information such as aperture details and the selected exposure mode are displayed. On digital SLRs, the LCD screen usually permits previewing of the image after it has been captured. A common screen size is 2.5 inches.
Light Metering System
This assists in choosing the best exposure levels for the shot. In most modern SLRs, instead of just metering one light reading of your image before capturing it, advanced or weighted light metering is carried out by matrix, segment, or pattern. This averages light readings from several areas of your image resulting in a more accurate overall setting.
Allows very close-up shots, typically from just a few centimetres away. The availability of this mode will be determined by the lens used: not all lenses have a macro setting.
This is generally for the more professional user. It allows manual selection of aperture, shutter speed and other parameters to suit an individual shot. In some cases, these can be selected from the on-screen menu.
This is a unit of measurement of an image and is used to describe the maximum resolution of a digital SLR. A megapixel consists of one million pixels. The greater the number of mega pixels, the more detailed the image that can potentially be captured. Whilst cameras are appearing with ever higher resolutions, it is important that you are realistic about the images to be captured. If you spend most of your time taking snapshots and printing them in 10 x 8" format, there is little point in a 12 megapixel camera. For those intending to produced enlarged prints, however, it is worth opting for a camera with 7 mega pixels or above.
A removable solid state media card that can be inserted into a camera for the storage of digital images. Card formats vary widely, the most common including secure digital (SD) and MMC formats. Many photo printers now allow you to print directly from a memory card so it is essential that you check compatibility.
Unwanted signals particularly at high ISO settings and with long exposure times can cause image degradation, usually appearing as "graininess" or tiny areas of poor colour rendition.
This allows the adjustment of the focal range length of a lens, thus making the subject appear closer or further away. Zoom lenses are generally defined by the minimum and maximum focal length, for example 28-80mm. Some SLR cameras incorporate motorised zoom whilst others will require you to manually adjust the zoom via a ring on the lens. Optical zoom has the advantage over its digital counterpart in that image degradation is minimal since there is no software manipulation of the image required. It is of course the only option from non-digital SLRs. It doesn't generally offer the same degree of magnification as that provided by some digital zoom functions which may provide for 100x zoom or more.
Allows connection from a camera via a cable directly to a printer, removing the need for a computer. Check compatibility if you intend to use PictBridge.
Red Eye Compensation / Reduction
Red eye is caused by the light from a camera flash reflecting onto and back from the retina at the back of a subject's eye. Red eye compensation takes two forms. Firstly, the camera may fire the flash in a rapid series of lower output bursts prior to the main flash which has the effect of forcing the subject's irises to contract, thus reducing the light passed to and reflected from the retina. Secondly, some digital SLRs may automatically detect the presence of eyes in the captured image using image recognition software and change the colour balance in this area accordingly.
RAW Image Format
A storage format in digital SLRs that captures the unmodified and uncompressed image data from each photo that you take. This generally requires a great deal of storage as the data is uncompressed. These photos can be viewed and tailored using dedicated software and then saved perhaps as a JPEG file.
SD Card (Secure Digital Card)
A compact form of memory card in common use.
Shot After Shot
This indicates minimal time delay for camera recovery between shots. See also frames / second above.
Many SLR cameras will come with a variety of present modes designed to optimise the camera's settings to certain shooting conditions. Common examples include Auto, Landscape, Portrait, Night Mode, Macro and Sport mode.
Shutter Speed Control
The shutter is a blade which is usually 'closed' thus preventing light from entering the camera until the shutter button is pressed, at which point the shutter will open fleetingly to the required setting, allowing light to pass through and the shot to be captured. The speed of the shutter , in combination with the aperture size (see above), determines how much light from the image is allowed to enter the camera and fall onto the image sensor or film when the image is being captured. For the capture of fast action shots, a faster shutter speed is required to avoid motion blur.
Shutter Priority Mode
Allows manual setting of the shutter speed. The camera will then automatically calculate the relevant exposure by the adjusting aperture size to compensate. This mode is particularly useful for fast action shots or at the opposite end of the scale for taking artistic blurred photos, perhaps of traffic tail lights at night.
Single Lens Reflex (SLR)
SLR cameras use a moving mirror system and viewing pentaprism, which is located between the lens and the film or CCD sensor. It directs the light from the subject, reflecting it via a mirror at a 45 degree angle to the optical pentaprism, where it is reflected twice more until it passes through the viewfinder. An SLR camera thus doesn't employ a separate viewfinder. This ensures that the viewfinder image exactly mirrors that of the lens.
Spot Metering Mode
A mode used when there is a vast change in brightness between foreground and background. The area metered using this mode is in the central part of the viewfinder and covers about 1% to 3.5% of the viewing area.
This figure, typically shown as a fraction of a second, is the time the camera requires to initialise itself before it is ready to take a shot. This is particularly important for those who may want to take shots in an environment where the unexpected can occur.
A USB (Universal Serial Bus) cable allows high speed data transfer between devices. USB 2.0 is a still faster standard. Many camera owners will wish to transfer image data between a camera and a computer. Since almost all PCs and laptops have USB connections, this is a good option. You will need appropriate imaging software (which often accompanies the camera) in order to manage and manipulate the images.
See SLR above.
The choice between a heavier more stable camera, and a lighter weight model for a more comfortable hold is a matter of personal preference. In general terms, the more sophisticated a camera is, the greater the weight. Many serious photographers regard physical weight as an enormously important factor. A camera of the right weight can assist in stability and thus image quality when taking a shot. There is no substitute for holding the camera yourself before making a purchase. Weight is also affected by the choice of lens and indeed the number of lenses and other supporting equipment that may be required such as external flashes and separate (heavy) flash power packs.
White balance determines whether the colour temperature of the white colour you see in an image, is the same as in the real thing. Many SLR cameras allow you to adjust this. Some automatic adjustment, others offer a variety of modes which may include Auto, Manual, Preset and Custom depending on the camera.
See optical zoom and digital zoom above.
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