An internal focus lens (sometimes known as IF) is a
photographic lens
A camera lens (also known as photographic lens or photographic objective) 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 capa ...
design in which
focus
Focus, or its plural form foci may refer to:
Arts
* Focus or Focus Festival, former name of the Adelaide Fringe arts festival in South Australia Film
*''Focus'', a 1962 TV film starring James Whitmore
* ''Focus'' (2001 film), a 2001 film based ...
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
A polarizer or polariser is an optical filter that lets light waves of a specific polarization pass through while blocking light waves of other polarizations. It can filter a beam of light of undefined or mixed polarization into a beam of well ...
or a petal shaped
lens hood
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 with ...
. During
macro photography
Macro photography (or photomacrography or macrography, and sometimes macrophotography) 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 gre ...
, 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.
"Measuring focal length"
/ref>
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
* Breathing (lens) Breathing originally referred to any geometric change in field-of-view when changing focus distance. Even if the angle-of-view is constant distortion changes will cause visible breathing. It has been recently used by photographers for changes of foc ...
References
Photographic lenses
{{Photo-stub