Hyperfocal Distance - The hyperfocal distance of a lens is a focus setting based on the closest point at which the lens can be focused and still maintain focus at infinity based on the lens's aperture setting (f/stop).
As an example, a 24mm lens set at f/11 and the focus distance set to 4.9' (1.5 m) will have a depth of focus ranging from infinity to about 2.3' (70 cm) from the camera position. Focusing a lens to its hyperfocal distance is a popular method of capturing spontaneous, journalistic-style photography and ensuring sharp focus throughout the frame.
The hyperfocal distance of a lens can be determined using the following formula: Hyperfocal distance = f2 / (d âˆ™ F); where f is the focal length, d is the minimum circle of confusion diameter, and F is the F-number.
Image Circle - The diameter of the circular image formed by the camera lens and focused onto the imaging sensor. The size of the image circle must be large enough to cover all four corners of the camera's rectangular image field. Full-frame cameras require image circles at least as wide as the diagonal of a 24 x 36mm frame, while APS-C format cameras require lenses that can cover the slightly smaller diagonal of the smaller sensor size.
Canon EF lenses have an image circle of approximately 43.2mm. Canon's EF tilt-shift (TS-E) lenses have an image circle of approximately 58.6mm in order provide extended image coverage for tilt and shift movements.
Image Distance - The distance between the rear principal point of the lens to the focal point (film plane), which varies according to the focus point of the lens.
Image Magnification - The image-size ratio between the physical size of the subject and the physical size of the imaging sensor or film. A macro lens that can focus down to life-size, or 1:1, will reproduce the subject at life size. A macro lens that can focus down to half life size, or 1:2, will record the subject at half of its actual size.
Image Stabilization (IS) - A technology that makes it possible to capture sharp photographs at shutter speeds up to four stops slower than normally recommended. Optical image stabilization, the type used by Canon, uses vibration-sensitive sensors to detect and measure the degree of vibration. These measurements are then used to rapidly shift a motorized set of elements inside the lens in the opposite direction of the vibration, effectively neutralizing any image blur.
Internal Focusing - Internal focusing is a lens design in which the length of the lens barrel remains constant regardless of whether the lens is focused at infinity or at its closest focusing point. This is achieved by having one or more of the lens groups shift within the confines of the lens barrel rather than having to extend outwards as the lens focuses closer.
Internal-focusing lenses tend to be more compact, and because the barrel doesn't rotate during focusing, internal-focus lenses are preferable for use with polarizing filters.
Lens - One or more concave, convex, or aspheric elements that can focus a light image on a focal plane (camera sensor or film).
Lens Barrel - A metal, polycarbonate, or plastic tube that holds the lens elements, and other lens components if applicable, in place.
Lens Cap - Protective cover that screws, snaps, or clips onto the front and rear of the lens to keep dust and other foreign particles off of the surfaces of the exposed front and rear lens elements.
Lens Mount - The metal or plastic coupling at the rear of the lens that connects the lens to the camera mount.
Lens Speed - A term describing the widest (fastest) aperture of a lens.
Lens Type - Categorization of a camera lens based on the number of elements it contains, its focal length, maximum aperture, and intended use.
Light (Visible Spectrum) - Light, i.e., the visual spectrum, consists approximately of the 400 to 700 nanometer portion of a greater known range of electromagnetic frequencies that include infrared and ultraviolet radiation, and wavelengths that transmit radio and TV broadcasts. Traveling at about 186,282.4 miles per second, light is the basis of photography.
Linear Polarizing Filter (Circular Polarizing Filter and Polarizing Filter) - Linear polarizers, which look and work identically to circular polarizers, are strictly for use with manual focus lenses and manual exposure metering. Due to the lack of a quarter wave plane, linear polarizers are not accurate when used with autofocus lenses, and can interfere with the accuracy and functionality of the AF and AE system.
Macro Lens - Unlike traditional curved-field lenses, in which the edges of the frame are not always as sharp as the center of the frame, macro lenses are flat-field lenses that maintain edge-to-edge sharpness when photographing flat subjects (documents, artwork, etc.) from an angle parallel to the subject. As the name implies, macro lenses can also focus closer to the subject than standard lenses, typically down to full (1:1) or half life size (1:2).
Canon produces macro lenses in five focal lengths-50mm, 60mm, 100mm, 180mm, and a 65mm lens with the ability to focus as close as 5x life size for extreme macro applications.
Macro Mode - Macro mode is a close-focusing mode found on many lenses, particularly zoom lenses. When engaged, macro mode enables the lens to focus closer than the lens's standard close-focusing distance.
Even though macro mode enables close focusing, the image quality of the same close-up captured with a true macro lens will usually be significantly better. Nonetheless, macro mode is a handy feature to have on any lens.
Maximum Aperture - The widest aperture of a lens.
Maximum Magnification - The maximum size ratio of the subject when the lens is at its closest focusing distance.
Medium Telephoto - A lens with a focal length between 85mm (28º30' AoV) and 135mm (18º AoV) on a full-frame camera.
Minimum Aperture - The smallest aperture of a lens.
Mechanical Distance - The measured distance from the leading edge of the lens barrel to the film plane.
Mirror Lens (Catadioptric Lens, Reflex Lens) - Essentially a short telescope, mirror lenses use curved, counter-reflective mirrors in place of glass elements that enable the design of short, lightweight telephoto lenses typically ranging in focal length from 300mm to 1000mm. Some inherent attributes of mirror lenses are that they have only one fixed aperture, usually about f/8; are capable of complete elimination of chromatic aberrations; and produce distinctive doughnut-shaped bokeh.
MTF Chart (Modulation Transfer Function)MTF charts are used to objectively measure the optical performance potential of a lens and utilize pairs of lines, organized perpendicular to one another, and at 30 lines/mm and 10 lines/mm, to measure the contrast and resolution resolving abilities of a lens against a theoretically perfect lens. Canon publishes MTF test results for each of its lenses at two aperture settings-the widest aperture and at f/8, both with the lens focused at infinity.
Normal Lens (Standard Lens) - A lens that has a focal length equal, or close, to the diagonal of the sensor or film. A normal lens for a full-frame sensor or 35mm film is approximately 50mm, and 35mm for APS-C format cameras. Normal lenses have a diagonal angle of view of about 46º.
Optical Axis - The straight line which passes through the hypothetical centerline connecting the center of curvature of each lens surface within a lens.
Optical Zoom - A zoom lens is an optical zoom. Unlike digital zoom, which is no more than a form of image cropping and interpolation, a zoom lens brings subjects variably closer by physically changing the effective focal length of the lens. Because the image quality remains virtually constant regardless of how tightly the subject is framed, optical zoom is a superior method of tightly framing a subject compared to other means of zooming.
Source: Canon USA