Focal Lengths

Objektive_Olympus [Abbildung: Olympus]What is the correct focal length? The answer to this question depends on personal preference as well as image subject. Over time, many photographers find their favourite focal length to work with. Henri Cartier Bresson used e.g. 50 mm. This focal length is about a human's range of vision. Many photojournalists during the Analog or even the Leica-M-era in contrast used 35 mm focal lengths. Sport journalists on the other hand use telephoto focal lengths. Various focal lengths are used depending on preference and emphasis. Most photographers today use lenses with variable focal lengths (zoom lens).

What is the correct focal length? The answer to this question depends on personal preference as well as image subject. Over time, many photographers find their favourite focal length to work with. Henri Cartier Bresson used e.g. 50 mm. This focal length is about a human's range of vision. Many photojournalists during the Analog or even the Leica-M-era in contrast used 35 mm focal lengths. Sport journalists on the other hand use telephoto focal lengths. Various focal lengths are used depending on preference and emphasis. Most photographers today use lenses with variable focal lengths (zoom lens).

Objektive_Olympus [Abbildung: Olympus]

The focal length of an optical system is the distance from the lens system to its focal point. In photography this distance is indicated in millimetre (mm). The photographic effect of focal length also depends on the image format (the size of image sensor or film).

As various sensor formats are available and a simple comparison of the lens systems‘ focal lengths would make little sense, most manufacturers provide information about the cameras 35mm film equivalent focal lengths. This information is helpful to photographers as it creates a basis for comparison. On single-lens flex cameras, this 35mm film equivalent can be calculated using a crop factor (also known as focal length multiplier). More information on crop factor can be found here.

The various focal lengths are usually divided into three categories (information according to 35 mm film equivalent focal lengths):

  • Focal length <40mm – wide angle
  • Focal length >40mm - 60mm – normal focal lengths
  • Focal length >60 –telephoto focal lengths

Because this type of distinction is not flexible enough, information is often combined e.g. 20mm wide angle. The lower the focal length’s value is, the wider the image angle (image section).

Important! – When buying a camera check the optical zoom. This enables images to be captured with almost unvarying image quality but with different focal lengths. Digital zooming happens at the expense of image quality and is ultimately just the trimmings of an image. This can usually be done in higher quality in post-processing programs.

Each focal length has its own creative characteristics. The targeted use of different focal lengths expands the options for creating an image substantially. These options are illustrated in the following articles.

The light intensity of a lens is indicated by the diaphragm’s maximum diameter. The lens’s light intensity depends on the diameter of the lens and the focal length. The maximum diameter of a diaphragm with a lens of 50mm by 100mm yields a maximum diaphragm opening of 1:2.0. A 200mm lens with the same opening has a light intensity of 1:4.0. The light intensity of a lens can therefore be calculated as follows:

Light intensity = maximum lens opening in mm / focal length in mm

The following values illustrate the classic f-number.
1:1,0 / 1:1,4 / 1:2,0 / 1:2,8 / 1:4,0 / 1:5,6 / 1:8,0 / 1:11,0 / 1:16,0 / 1:22,0 / 1:32,0

All of the values on the right hand side represent half of the quantity of light compared to the precedent value. To compensate for this, exposure time should be doubled in unvarying lighting conditions.

A high lens light intensity is an important criterion especially in poor lighting conditions and fast motion. A wide diaphragm opening in relation to determining the depth of field is also desirable in portrait photography. More on depth of field can be found in the respective article.

Normal 0 21 false false false MicrosoftInternetExplorer4 Welche Brennweite ist die Richtige? Diese Frage ist sowohl von den eigenen Vorlieben als auch vom Motiv abhängig. Viele Fotografen finden mit der Zeit ihre Lieblingsbrennweite. Henri Cartier Bresson nutze z. B. 50 mm. Diese Brennweite entspricht etwa dem Blickfeld des Menschen. Viele Fotojournalisten der Analog- oder vielleicht besser Leica-M-Ära nutzten hingegen 35-Millimeter-Brennweiten.
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