Internal focusing

Last updated

An internal focus lens (sometimes known as IF) is a photographic lens design in which focus is shifted by moving the inner lens group or groups only, without any rotation or shifting of the front lens element. This makes it easy to use, for example, a screwed-in polarizing filter or a petal shaped lens hood. During macro photography, using an internal focus lens reduces the risk of the front of the lens accidentally hitting the subject during focusing as the front element does not move. [1]

Focus (optics) point where light rays originating from a point converge on an object

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics. In the absence of significant aberrations, the smallest possible blur circle is the Airy disc, which is caused by diffraction from the optical system's aperture. Aberrations tend to get worse as the aperture diameter increases, while the Airy circle is smallest for large apertures.

Lens hood photographic equipment

In photography, a lens hood or lens shade is a device used on the front end of a lens to block the Sun or other light source(s) to prevent glare and lens flare. Lens hoods may also be used to protect the lens from scratches and the elements without having to put on a lens cover.
The geometry of a lens hood is dependent on three things: the focal length of the lens, the size of the front lens element and the dimensions of the image sensor or film in the camera.

The physical size of an internal focusing lens does not change during focus, nor does the front of the lens rotate. This is particularly useful for large lenses, keeping the size more compact, or when using filters or accessories mounted on the front of the lens that may require careful alignment. One issue internal focusing lens can have is that the true focal length of the lens is reduced when not focused at infinity.

See also

Related Research Articles

View camera type of camera

A view camera is a large format camera in which the lens forms an inverted image on a ground glass screen directly at the plane of the film. The image viewed is exactly the same as the image on the film, which replaces the viewing screen during exposure.

Camera lens optical lens or assembly of lenses used with a camera body and mechanism to make images of objects

A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.

Wide-angle lens

In photography and cinematography, a 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. This type of lens allows more of the scene to be included in the photograph, which is useful in architectural, interior and landscape photography where the photographer may not be able to move farther from the scene to photograph it.

Telephoto lens

In photography and cinematography, a 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. This is achieved by incorporating a special lens group known as a telephoto group that extends the light path to create a long-focus lens in a much shorter overall design. The angle of view and other effects of long-focus lenses are the same for telephoto lenses of the same specified focal length. Long-focal-length lenses are often informally referred to as telephoto lenses although this is technically incorrect: a telephoto lens specifically incorporates the telephoto group.

Photographic filter filter ND

In photography and cinematography, a filter is a camera accessory consisting of an optical filter that can be inserted into the optical path. The filter can be of a square or oblong shape and mounted in a holder accessory, or, more commonly, a glass or plastic disk in a metal or plastic ring frame, which can be screwed into the front of or clipped onto the camera lens.

Eyepiece type of lens attached to a variety of optical devices such as telescopes and microscopes; usually the lens that is closest to the eye when someone looks through the device, placed near the focal point of the objective to magnify the image

An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is so named because it is usually the lens that is closest to the eye when someone looks through the device. The objective lens or mirror collects light and brings it to focus creating an image. The eyepiece is placed near the focal point of the objective to magnify this image. The amount of magnification depends on the focal length of the eyepiece.

Canon EF lens mount standard lens mount on the Canon EOS family

The EF lens mount is the standard lens mount on the Canon EOS family of SLR film and digital cameras. EF stands for "Electro-Focus": automatic focusing on EF lenses is handled by a dedicated electric motor built into the lens. Mechanically, it is a bayonet-style mount, and all communication between camera and lens takes place through electrical contacts; there are no mechanical levers or plungers. The mount was first introduced in 1987.

Macro photography photography genre and techniques of extreme close-up pictures

Macro photography, is extreme close-up photography, usually of very small subjects and living organisms like insects, in which the size of the subject in the photograph is greater than life size . By the original definition, a macro photograph is one in which the size of the subject on the negative or image sensor is life size or greater. However, in some uses it refers to a finished photograph of a subject at greater than life size.

Lens mount interface between a photographic camera body and a lens

A lens mount is an interface – mechanical and often also electrical – between a photographic camera body and a lens. It is confined to cameras where the body allows interchangeable lenses, most usually the rangefinder camera, single lens reflex type or any movie camera of 16 mm or higher gauge. Lens mounts are also used to connect optical components in instrumentation that may not involve a camera, such as the modular components used in optical laboratory prototyping which join via C-mount or T-mount elements.

Canon EF 50mm lens Wikimedia disambiguation page

The EF 50mm lenses are a group of normal prime lenses made by Canon that share the same focal length. These lenses are based on the classic double-Gauss lens, with the f/1.8 being a standard six-element double-Gauss with an air gap and powers between element 2 and 3 and its faster cousins adding additional elements. The 50mm focal length, when used with a 35mm film or full-frame sensor, has been widely considered to match the perspective seen by the human eye.

Large format lens

Large format lenses are photographic optics that provide an image circle large enough to cover large format film or plates. Large format lenses are typically used in large format cameras and view cameras.

The EF 35 mm lenses are four wide angle prime lenses with EF mount made by Canon Inc. The family also includes one EF-S lens that only mounts on Canon bodies with APS-C sensors. Due to the 1.6 crop factor of Canon APS-C sensors, all of the 35 mm lenses have a 35 mm equivalent focal length of 56 mm, making them normal lenses on APS-C bodies.

Canon EF 85mm lens camera lens

The EF 85mm lenses are a group of medium telephoto prime lenses made by Canon Inc. that share the same focal length. These lenses have an EF type mount that fits the Canon EOS line of cameras.

Canon L lens

Canon's series of L lenses are a professional line of photography lenses made by Canon. Canon has sold zoom and prime L-series lenses for the discontinued FD lens mount, for the current EF lens mount used on all Canon EOS SLR cameras and for the RF mount used on full-frame mirrorless interchangeable-lens cameras.

Close-up lens

In photography, a close-up lens is a simple secondary lens used to enable macro photography without requiring a specialised primary lens. They work like reading glasses, allowing a primary lens to focus more closely. Bringing the focus closer allows the photographer new creative possabilities with their lenses.

The design of photographic lenses for use in still or cine cameras is intended to produce a lens that yields the most acceptable rendition of the subject being photographed within a range of constraints that include cost, weight and materials. For many other optical devices such as telescopes, microscopes and theodolites where the visual image is observed but often not recorded the design can often be significantly simpler than is the case in a camera where every image is captured on film or image sensor and can be subject to detailed scrutiny at a later stage. Photographic lenses also include those used in enlargers and projectors.

Pancake lens

A pancake lens is colloquial term for a flat, thin lens, generally a normal or slightly wide prime lens for a camera.

Sigma 8–16mm f/4.5–5.6 DC HSM lens

The Sigma 8–16mm lens is an enthusiast-level, ultra wide-angle rectilinear zoom lens made by Sigma Corporation specifically for use with APS-C small format digital SLRs. It is the first ultrawide rectilinear zoom lens with a minimum focal length of 8 mm, designed specifically for APS-C size image sensors. The lens was introduced at the February 2010 Photo Marketing Association International Convention and Trade Show. At its release it was the widest viewing angle focal length available commercially for APS-C cameras. It is part of Sigma's DC line of lenses, meaning it was designed to have an image circle tailored to work with APS-C format cameras. The lens has a constant length regardless of optical zoom and focus with inner lens tube elements responding to these parameters. The lens has hypersonic zoom autofocus.

References