Terminology

is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An optical system typically has many openings or structures that limit the ray bundles.

Aperture priority

often abbreviated A or Av on a camera mode dial, is a setting on some cameras that allows the user to set a specific aperture value while the camera selects a shutter speed to match it that will result in proper exposure based on the lighting conditions as measured by the camera's light meter.

Bokeh

is the aesthetic quality of the blur produced in out-of-focus parts of an image. Bokeh has also been defined as "the way the lens renders out-of-focus points of light". Differences in lens aberrations and aperture shape cause very different bokeh effects.

Exposure

is the amount of light per unit area reaching a frame of photographic film or the surface of an electronic image sensor, as determined by shutter speed, lens aperture, and scene luminance.

Focal length

is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative focal length indicates that the system diverges light.

F-number or F-Stop

is the ratio of the system's focal length to the diameter of the entrance pupil. It is also known as the focal ratio, f-ratio, or f-stop, and is very important in photography.

ISO

is one of the three pillars of the photography exposure triangle, along with shutter speed and aperture, that you can adjust when capturing a photo.

ISO controls the amount of light that your camera lets in and has a huge impact on the darkness or light in your photos — something you might adjust for technical or artistic reasons.

Originally, ISO numbers were set by the International Organization for Standardization (where the name ISO comes from) to refer to the sensitivity of the film in a camera to light. ISO standards in digital photography today still have the same numbering system to indicate the sensitivity of a digital camera sensor to light.

Prime lens

is a fixed focal length photographic lens, typically with a maximum aperture from f2.8 to f1.2. The term can also mean the primary lens in a combination lens system. Confusion between these two meanings can occur if context doesn't make the interpretation clear.

Shutter

is a device that allows light to pass for a determined period, exposing photographic film or a photosensitive digital sensor to light in order to capture a permanent image of a scene.

Shutter priority

(usually denoted as S on the mode dial), also called time value (abbreviated as Tv), refers to a setting on some cameras that allows the user to choose a specific shutter speed while the camera adjusts the aperture to ensure correct exposure.

Shutter speed

is the length of time that the digital sensor inside the camera is exposed to light when taking a photograph. 1⁄500 of a second will let half as much light in as 1⁄250. Shutter speed is responsible for two particular things: changing the brightness of your photo and creating dramatic effects by either freezing action or blurring motion. Quick shutter speeds freeze action, while long ones create an effect of motion when you photograph moving objects. If you use a long shutter speed, your camera sensor gathers a lot of light, and the resulting photo will be quite bright. By using a quick shutter speed, your camera sensor is only exposed to a small fraction of light, resulting in a darker photo. However, shutter speed is not the only variable that affects the brightness of an image. There are also Aperture and ISO, along with the actual brightness of the scene in front of you. Long shutter speeds are typically above 1 second – at which point, you will need to use a tripod to get sharp images.

Lens filters

- UV filter - a lens filter, UV stands for Ultraviolet, used to filter out ultraviolet rays from the sun
- CPL filter - a lens filter, CPL stands for Circular Polarised Linear, used to control glare
- FLD filter - a lens filter, FLD stands for Fluorescent Light Daylight, used to control white balance

Types of lenses

Telephoto lens

is a specific type of a long-focus lens in which the physical length of the lens is shorter than the focal length.

Wide-angle lens

refers to a lens whose focal length is substantially smaller than the focal length of a normal lens for a given film plane.

Zoom lens

is a mechanical assembly of lens elements for which the focal length can be varied, as opposed to a fixed focal length lens. A true zoom lens, also called a parfocal lens, is one that maintains focus when its focal length changes.