R. McPhee Learning Photography

The opening created by a series of blades making up the lens diaphragm. These blades combine to form a circular opening whose size is dependent upon the aperture setting selected by the photographer.

Autofocus (or AF) is a feature of some optical systems that allows them to obtain (and in some systems to also continuously maintain) correct focus on a subject, instead of requiring the operator to adjust focus manually.

Bit depth, is a computer graphics term describing the number of bits used to represent the color of a single pixel in a bitmapped image or video frame buffer. This concept is also known as bits per pixel (bpp), particularly when specified along with the number of bits used. Higher color depth gives a broader range of distinct colors.

Color depth is only one aspect of color representation (formally, the gamut: which colors can be expressed), expressing how finely levels of color can be expressed (formally, gamut depth); the other aspect is how broad a range of colors can be expressed. The RGB color model, as used below, cannot express many colors, notably saturated colors such as yellow. Thus, the issue of color representation is not simply "sufficient color depth" but also "broad enough gamut".

There are a couple of definitions of bracket as it applies to photography. When used as a verb, bracketing is taking multiple photos of the same basic scene at varying exposures in an attempt to get at least one good exposure. Some cameras even offer an auto-bracketing function in which the camera fires three shots at different exposures. When used as a noun, a bracket is an L-shaped device mounted to the bottom of your camera used to reposition your flash in an attempt to reduce the likelihood of red-eye and eliminate harsh shadows.

Color digital images are made of pixels, and pixels are made of combinations of primary colors. A channel in this context is the grayscale image of the same size as a color image, made of just one of these primary colors. For instance, an image from a standard digital camera will have a red, green and blue channel. A grayscale image has just one channel.

In the digital realm, there can be any number of conventional primary colors making up an image; a channel in this case is extended to be the grayscale image based on any such conventional primary color. By extension, a channel is any grayscale image the same size with the "proper" image, and associated with it.

The CMYK color model, referred to as process color or four color, is a subtractive color model, used in color printing, also used to describe the printing process itself. CMYK refers to the four inks used in most color printing: cyan, magenta, yellow, and key black. Though it varies by print house, press operator, press manufacturer and press run, ink is typically applied in the order of the abbreviation.

The “K” in CMYK stands for key since in four-color printing cyan, magenta, and yellow printing plates are carefully keyed or aligned with the key of the black key plate. Some sources suggest that the “K” in CMYK comes from the last letter in "black" and was chosen because B already means blue.[1][2] However, this explanation, though plausible and useful as a mnemonic, is incorrect.[3]

The CMYK model works by partially or entirely masking certain colors on the typically white background (that is, absorbing particular wavelengths of light). Such a model is called subtractive because inks “subtract” brightness from white.

In additive color models such as RGB, white is the “additive” combination of all primary colored lights, while black is the absence of light. In the CMYK model, it is just the opposite: white is the natural color of the paper or other background, while black results from a full combination of colored inks. To save money on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink instead of the combination of cyan, magenta and yellow.

In digital photography, a crop factor is related to the ratio of the dimensions of a camera's imaging area compared to a reference format; most often, this term is applied to digital cameras, relative to 35 mm film format as a standard. In the case of digital cameras, the imaging device would be a digital sensor. The most commonly used definition of crop factor is the ratio of a 35 mm frame's diagonal (43.3 mm) to the diagonal of the image sensor in question; that is, CF=diag35mm / diagsensor. Given the same 3:2 aspect ratio as 35mm's 36mm x 24mm area, this is equivalent to the ratio of heights or ratio of widths; the ratio of sensor areas is the square of the crop factor.

This ratio is also commonly referred to as a focal length multiplier ("FLM") since multiplying a lens focal length by the crop factor or FLM gives the focal length of a lens that would yield the same field of view if used on the reference format.

The term format factor is sometimes also used, and is a more neutral term that corresponds to the German word for this concept, Formatfaktor.

A method of softening and reducing light or softening an image through filtration. There are several different forms of diffusion used in photography. You can diffuse light by placing diffusion material between your light source and your subject, by mounting a filter on your camera’s lens, or by creating diffusion effect in Photoshop. The effect of each of these methods is different. You can’t necessarily substitute one for the other.

Digital cameras can do things film cameras cannot: displaying images on a screen immediately after they are recorded, storing thousands of images on a single small memory device, recording video with sound, and deleting images to free storage space. Some can crop pictures and perform other elementary image editing. Fundamentally they operate in the same manner as film cameras, typically using a lens with a variable diaphragm to focus light onto an image pickup device. The combination of the diaphragm and a shutter mechanism is used to admit the correct amount of light to the imager, just as with film; the only difference is that the image pickup device is electronic rather than chemical.

Digital cameras are incorporated into many devices ranging from PDAs and mobile phones (called camera phones) to vehicles. The Hubble Space Telescope and other astronomical devices are essentially specialized digital cameras.