Focal length of the lens Is one of the most important lens parameters. The focal length of a lens indicates how far or close (broad) the lens can 'encounter'.

Focal length is measured in millimeters, centimeters and meters. For example, the designation of the fixed lens Nikon 85mm F / 1.8D AF Nikkor says that his focal length is fixed and is 85 millimeters. A designation Tamron 28-200mm 1: 3.viii-5.vi Macro AF Aspherical XR (IF) A03 suggests that the focal length of the lens can vary from 28 millimeters to 200 millimeters. Lenses in which the focal length can vary are called zoom lens (zoom lens, zoom lens). Zoom ratio is calculatedI am dividing a larger number by a smaller one, in this case 200mm \ 28mm = 7 times.

Normally, the larger the focal length of the lens, the larger the size of the lens itself, especially its length.

Focal length Is the outset thing to look for when choosing a lens. It shows what angle of view the camera will capture when working with one or another lens.

Attention: the focal length of the lens is the physical size of the lens itself, it does not change and does non depend on the type of cameraon which the lens is used. Merely for cropped cameras and for cameras with different physical matrix sizes, the parameter EGF (Equivalent Focal Length), it shows the real viewing angle for a 35mm film, which is obtained when using one lens or some other on cameras with different matrix sizes. More details in the section crop factor.

Here is an example of how the space that the camera can cover when using lenses with dissimilar focal lengths changes.

17mm

24mm

35mm

50mm

70mm

85mm

100mm

135mm

200mm

300mm

For examples, I used a camera Nikon D200mounted on a tripod. All photos were taken at F / v.half dozen, the following lenses were used:

• 17mm, 24mm - Tamron AF 17-50mm f / 2.8 XR Di Ii LD Aspherical (IF) for Nikon
• 35mm - Nikon 35mm f / 1.8G AF-Due south DX Nikkor
• 50mm - Helios-81N 50mm F2.0 MC
• 70mm, 100mm, 200mm, 300mm - Nikon 70-300mm f / 4.five-5.6G IF-ED AF-S VR Zoom-Nikkor
• 85mm - Nikon 85mm F / 1.8D AF Nikkor
• 135mm - Jupiter-37A 135mm F3.5

It is often said that the photographer should take a fix of lenses that covers the desired range of focal lengths and thus covers all possible situations in the work of the lensman. 1 of the most archetype sets for full-frame cameras tin be considered: 14-24mm, 24-70mm, seventy-200mm, 200-400mm. For cropped cameras, ordinarily a proficient gear up consists of eleven-16mm, sixteen-50mm, 50-135mm lenses. Covering the entire range of focal lengths is not worth chasing; you tin safely do without a single fixed lens. The division into different types of lenses can be found here.

In improver to the angle (field) of view, the focal length affects the perspective of the image (due to the difference in distance to the discipline with equal proportions of the subject). At different focal lengths, the sizes of objects are correlated differently in photographs. Long-focus lenses bring closer non just the subject itself, but also the unabridged space behind the subject and in front of the focus discipline. And wide-angle lenses average the sizes of all elements in photographs. Besides, different focal lengths impact to blur the groundwork.

17 mm

24 mm

35 mm

fifty mm

70 mm

85 mm

100 mm

135 mm

200mm (195)

300 mm

Personal feel:

I do not like to convert the focal length from millimeters to degrees of field of view, who is interested, then there is an commodity on Radozhiv 'Relationship between focal length, viewing angle, and focus distance'. In practice, it is enough to sympathise what the approximate angles are given past a lens with a certain focal length in order to intuitively know how some other longer or wider lens will deport on the camera. Advise experiment with the lens simulator. There is even so an interesting commodity nigh dependence of the focal length of the lens on the focusing altitude.

Conclusions:

The choice of a lens, first of all, entails determining the desired focal length range. Focal length indicates how broad or narrow the lens 'sees'. Focal length is very important to the mistiness zone of the blur zone and perspective images.

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