In
photography
Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employe ...
, the 35 mm equivalent focal length is a measure that indicates the
angle of view of a particular combination of a
camera
A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with a ...
lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...
and film or
sensor size. The term is popular because in the early years of digital photography, most photographers experienced with interchangeable lenses were most familiar with the
35 mm film 35 mm may refer to:
* 135 film, a type of still photography format commonly referred to as 35 mm film
* 35 mm movie film
35 mm film is a film gauge used in filmmaking, and the film standard. In motion pictures that record on f ...
format.
On any 35 mm film camera, a 28 mm lens is a
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 ...
, and a 200 mm lens is a
long-focus lens
In photography, a long-focus lens is a camera lens which has a focal length that is longer than the diagonal measure of the film or sensor that receives its image.
It is used to make distant objects appear magnified with magnification increasin ...
. However, now that digital cameras have mostly replaced 35 mm cameras, there is no uniform relation between the
focal length of a lens and the angle of view, since the size of the camera sensor also determines angle of view, and sensor size is not standardized as film size was. The 35 mm equivalent focal length of a particular lens–sensor combination is the focal length that one would need for a 35 mm film camera to obtain the same angle of view.
Most commonly, the 35 mm equivalent focal length is based on equal ''diagonal'' angle of view.
[What is "35 mm equivalent focal length?"](_blank)
The Panorama Factory, 2004. This definition is also in the
CIPA guideline DCG-001.
Alternatively, it may sometimes be based on ''horizontal'' angle of view. Since 35 mm film is normally used for images with an
aspect ratio (width-to-height ratio) of 3:2, while many digital cameras have a 4:3 aspect ratio, which have different diagonal-to-width ratios, these two definitions are often not equivalent.
Calculation
35 mm equivalent focal lengths are calculated by multiplying the actual focal length of the lens by the
crop factor
In digital photography, the crop factor, format factor, or focal length multiplier of an image sensor format is the ratio of the dimensions of a camera's imaging area compared to a reference format; most often, this term is applied to digital ca ...
of the sensor. Typical crop factors are 1.26× – 1.29× for Canon (1.35× for
Sigma "H")
APS-H
Advanced Photo System type-C (APS-C) is an image sensor format approximately equivalent in size to the Advanced Photo System film negative in its C ("Classic") format, of 25.1×16.7 mm, an aspect ratio of 3:2 and Ø 31.15 mm field d ...
format, 1.5× for
Nikon
(, ; ), also known just as Nikon, is a Japanese multinational corporation headquartered in Tokyo, Japan, specializing in optics and imaging products. The companies held by Nikon form the Nikon Group.
Nikon's products include cameras, camera ...
APS-C ("DX") format (also used by Sony, Pentax, Fuji, Samsung and others), 1.6× for
Canon
Canon or Canons may refer to:
Arts and entertainment
* Canon (fiction), the conceptual material accepted as official in a fictional universe by its fan base
* Literary canon, an accepted body of works considered as high culture
** Western ca ...
APS-C format, 2× for
Micro Four Thirds format, 2.7× for 1-inch sensors (used in Nikon 1 cameras and some Sony RX cameras), 5× to 6× for
compact digital cameras, and even higher for built-in cameras of
mobile device
A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physica ...
s like cell phones or tablets.
According to CIPA guidelines,
35 mm equivalent focal length is to be calculated like this:
"Converted focal length into 35 mm camera" = (Diagonal distance of image area in the 35 mm camera (43.27 mm) / Diagonal distance of image area on the image sensor of the
DSC DSC may refer to:
Academia
* Doctor of Science (D.Sc.)
* District Selection Committee, an entrance exam in India
* Doctor of Surgical Chiropody, superseded in the 1960s by Doctor of Podiatric Medicine
Educational institutions
* Dalton State Col ...
) × focal length of the lens of the DSC.
Depth of field equivalent
Quoted 35 mm equivalent focal lengths typically ignore
depth of field (DOF), which depends on both focal length and
aperture
In optics, an aperture 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 ...
. The DOF of smaller sensors is deeper at a given
f number
In optics, the f-number of an optical system such as a camera lens is the ratio of the system's focal length to the diameter of the entrance pupil ("clear aperture").Smith, Warren ''Modern Optical Engineering'', 4th Ed., 2007 McGraw-Hill Pro ...
, due to the smaller absolute aperture diameters corresponding to shorter focal length lenses.
Equivalent depth of field can be calculated the same way using the crop factor.
For example, a 50mm f/2 lens on a 2× crop factor Micro Four Thirds camera would be equivalent to a 100 mm (= 2×50 mm) f/4 (= f/(2×2)) lens on a
full-frame digital SLR
A full-frame DSLR is a digital single-lens reflex camera (DSLR) with a 35 mm image sensor format (). Historically, 35 mm was one of the standard film formats, alongside larger ones, such as medium format and large format. The full-fra ...
in terms of
field of view
The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.
Human ...
, depth of field, total light gathered, and diffraction effects.
Conversions
A standard 35 mm film image is 36 mm wide by 24 mm tall (35 mm refers to the height of the film including the perforations for film transport), and the diagonal is 43.3 mm. This leads to the following conversion formulas for a lens with a true focal length ''f'':
For historical reasons, sensor size specifications such as 1/2.5" do not match the actual sensor size, but are a bit larger (typically about a factor of 1.5) than the actual sensor diagonal.
[Vincent Bockaert]
Sensor sizes
DPreview.com. This is because these sensor size specifications refer to the size of a
camera tube
Video camera tubes were devices based on the cathode ray tube that were used in television cameras to capture television images, prior to the introduction of charge-coupled device (CCD) image sensors in the 1980s. Several different types of tub ...
, while the usable sensor size is about 2/3 of the size of the tube. Tubes are not used on digital cameras, but the same specifications are used.
Apart from the width- and diagonal-based 35 mm equivalent focal length definitions, there is a third definition: ''EFL'' = 50 ''f'' /''d'' mm.
However, it is not clear to what extent this definition is used.
References
External links
Focal Length Conversionfor
medium format
Medium format has traditionally referred to a film format in photography and the related cameras and equipment that use film. Nowadays, the term applies to film and digital cameras that record images on media larger than the used in 35&nbs ...
and
large format
Large format refers to any imaging format of or larger. Large format is larger than "medium format", the or size of Hasselblad, Mamiya, Rollei, Kowa, and Pentax cameras (using 120- and 220-roll film), and much larger than the frame ...
, at photo.net
Focal Lengthat
dpreview
''Digital Photography Review'', also known as ''DPReview,'' is a website about digital cameras and digital photography, established in November 1998. The website provides comprehensive reviews of digital cameras, lenses and accessories, buying g ...
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Science of photography