What is Focal Length? – Photography PX

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The resulting images from 50 mm and 70 mm lenses for different sensor sizes; 36×24 mm (red) and 24×18 mm (blue)

In photography, the
35 mm equivalent focal length
is a measure that indicates the angle of view of a particular combination of a camera lens and moving-picture show or sensor size. The term is useful considering most photographers experienced with interchangeable lenses are almost familiar with the 35 mm film format.

On whatsoever 35 mm film photographic camera, a 28 mm lens is a wide-angle lens, and a 200 mm lens is a long-focus lens. Even so, now that digital cameras accept mostly replaced 35 mm cameras, there is no uniform relation between the focal length of a lens and the bending of view, since the size of the camera sensor likewise determines bending of view, and sensor size is not standardized equally film size was. The 35 mm equivalent focal length of a particular lens–sensor combination is the focal length that ane would demand for a 35 mm picture camera to obtain the same angle of view.

About normally, the 35 mm equivalent focal length is based on equal
diagonal
bending of view.[1]
This definition is also in the CIPA guideline DCG-001.[2]
Alternatively, it may sometimes be based on
horizontal
angle of view. Since 35 mm film is ordinarily used for images with an aspect ratio (width-to-height ratio) of iii:2, while many digital cameras accept a 4:iii attribute ratio, which have different diagonal-to-width ratios, these two definitions are often not equivalent.

Adding

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35 mm equivalent focal lengths are calculated by multiplying the bodily focal length of the lens past the crop factor of the sensor. Typical crop factors are one.26× – 1.29× for Catechism (1.35× for Sigma “H”) APS-H format, 1.five× for Nikon APS-C (“DX”) format (too used by Sony, Pentax, Fuji, Samsung and others), 1.half-dozen× for Canon APS-C format, 2× for Micro Four Thirds format, 2.7× for 1-inch sensors (used in Nikon ane cameras and some Sony RX cameras), 5× to 6× for compact digital cameras, and even higher for built-in cameras of mobile devices like cell phones or tablets.

Co-ordinate to CIPA guidelines,[two]
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 paradigm sensor of the DSC) × focal length of the lens of the DSC.

Depth of field equivalent

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Quoted 35 mm equivalent focal lengths typically ignore depth of field (DOF), which depends on both focal length and aperture. The perceived DOF of smaller sensors is deeper due to the shorter focal length lenses.

Equivalent depth of field tin be calculated the same style using the crop factor.[iii]
For example, a 50mm f/2 lens on a 2× crop factor Micro 4 Thirds camera would be equivalent to a 100 mm (= ii×50 mm) f/iv (= f/(2×ii)) lens on a Total-frame digital SLR in terms of field of view, depth of field, full calorie-free gathered,[iv]
and diffraction furnishings.

Conversions

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A standard 35 mm moving picture image is 36 mm broad by 24 mm tall (35 mm refers to the height of the film including the perforations for picture transport), and the diagonal is 43.three mm. This leads to the following conversion formulas for a lens with a true focal length
f:

Image size diagonal-based EFL width-based EFL
4:3 (sensor width
w)
f
35
= 34.6
f
/w
mm
f
35
= 36.0
f
/westward
mm
4:iii (sensor diagonal
d)
f
35
= 43.3
f
/d
mm
f
35
= 45.0
f
/d
mm
3:two (sensor width
w)
f
35
= 36.0
f
/w
mm
f
35
= 36.0
f
/w
mm
iii:2 (sensor diagonal
d)
f
35
= 43.iii
f
/d
mm
f
35
= 43.3
f
/d
mm

For historical reasons, sensor size specifications such equally 1/2.5″ do not match the actual sensor size, but are a chip larger (typically about a factor of 1.5) than the actual sensor diagonal.[5]
This is because these sensor size specifications refer to the size of a camera tube, while the usable sensor size is near 2/three of the size of the tube. Tubes are non used on digital cameras, simply the aforementioned specifications are used.

Apart from the width- and diagonal-based 35 mm equivalent focal length definitions, there is a third definition:
EFL
= fifty
f
/d
mm.[1]
However, information technology is non clear to what extent this definition is used.[
citation needed
]

References

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  1. ^


    a




    b



    What is “35 mm equivalent focal length?” The Panorama Factory, 2004.
  2. ^


    a




    b




    “CIPA DCG-001-Translation-2005 Guideline for Noting Digital Camera Specifications in Catalogs”
    (PDF). Archived from the original
    (PDF)
    on 2017-02-02. Retrieved
    2015-10-19
    .



  3. ^


    Atkins, Bob. “Digital Depth of Field”. Retrieved
    23 May
    2012
    .



  4. ^


    Butler, Richard. “What is equivalence and why should I care?”.
    DPReview
    . Retrieved
    22 August
    2019
    .



  5. ^

    Vincent Bockaert, Sensor sizes. DPreview.com.

External links

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  • Focal Length Conversion for medium format and large format, at photo.net
  • Focal Length at dpreview



Source: https://en.wikipedia.org/wiki/35_mm_equivalent_focal_length