Telephoto lens
Telephoto lenses are lenses in general photographic parlance with a longer focal length and a smaller angle of view compared to a normal lens . They are mostly used to zoom in on objects that are further away, similar to binoculars, and so “bring them closer”. Another characteristic of the imaging properties of telephoto lenses is their shallow depth of field ; it is used when only the actual subject is to be shown in focus.
In technical optics, a telephoto lens is a lens with shortening optical elements, which leads to a shorter overall length than its nominal focal length.
properties
Telephoto lenses can be connected to suitable cameras as interchangeable lenses ; they are seldom permanently integrated into them. Telephoto lenses are not to be confused with zoom lenses that allow the focal length to be adjusted, but do not necessarily have to achieve a telephoto focal length.
In the field of macro photography , telephoto lenses allow a larger working distance between the lens and the subject than normal lenses or wide-angle lenses , which, for example, simplify the lighting options.
Telephoto lenses differ from long-range lenses in that the combination of a front positive group (converging lens) with a rear negative group (diverging lens) shifts the image-side main plane (H ') of the lens forward, thereby achieving a shorter overall length than the nominal focal length would correspond.
variants
Telephoto lenses can be divided into different classes depending on the focal length and primary application. The following groups refer to the small image format for the focal length and angle of view information, for other camera systems, especially digital cameras with smaller sensors, see format factor .
Portrait lenses
Portrait lenses with focal lengths between about 80 mm and 105 mm, sometimes up to 135 mm (all with 35mm cameras) are often used for portrait photography around the face due to the reduced depth of field and the image of human faces, which is perceived as pleasantly distortion-free, but not yet flat or to remove the person from the background. Lenses of this focal length range can usually still be used without a tripod in normal lighting conditions.
Typical portrait focal lengths are
- 85 mm (diagonal angle of view 28 ° 30 '),
- 100 mm (diagonal angle of view 24 °).
Standard telephoto lenses
The standard telephoto lenses are lenses with a focal length between about 135 and 200 mm (based on small images). These lenses are often used in travel , but also in nature photography . With lenses of this focal length range, except in very good lighting conditions or when using highly sensitive films, it is advisable to use a tripod to avoid blurring .
Typical standard celebrations are:
- 135 mm (diagonal angle of view 18 °);
- 180 mm
- 200 mm (diagonal angle of view 12.3 °).
Super telephoto lenses
Telephoto lenses with focal lengths from 200 (only with exceptional light intensity ) and 300 mm are considered super telephoto lenses in relation to the 35mm format . Especially in animal and sports photography , models with a high light intensity in the range from F1: 2.8 to F1: 4.0 are often used. Due to their high weight, these lenses can usually only be used with a tripod.
Typical super celebrity distances are:
- 200 mm (diagonal angle of view 12.3 °)
- 300 mm (diagonal image angle 8.2 °)
- 400 mm (diagonal angle of view 6.2 °)
- 500 mm (diagonal angle of view 5.0 °)
- 600 mm (diagonal angle of view 4.1 °)
- 800 mm (diagonal angle of view 3.1 °)
- 1200 mm (diagonal angle of view 2.1 °)
Mirror lens lenses
Mirror lens lenses are a special type of construction which, thanks to the “folded” beam path, make it possible to construct very compact lenses for large focal lengths. Due to their design, mirror lens objectives have some special features; a ring-shaped image of reflections, for example, is unavoidable with this type of objective. Mirror lens lenses are available for small format cameras with focal lengths between 250 mm and 2000 mm as well as for medium format cameras.
Comparison of different focal lengths of telephoto lenses
- Recordings with lenses of different focal lengths from a fixed position with a camera with a format factor of 1.6
70 mm focal length
100 mm focal length
135 mm focal length
200 mm focal length
300 mm focal length
500 mm focal length
1000 mm focal length
2000 mm focal length
Others
Telephoto lenses with a focal length of up to about 200 mm (based on a small image) with moderate light intensity can be constructed in a comparatively compact and inexpensive manner, even with very good image quality. At high light intensities and very long focal lengths, however, lens errors become more and more noticeable, so that considerable design effort has to be made. Such telephoto lenses require special optical glasses and aspherical lenses . Calcium fluoride lenses are sometimes used. Many super telephoto lenses are apochromatically corrected. In telephotography, the same rule of thumb applies as with normal lenses , namely that in order to achieve blur-free images with a shutter speed that is shorter than the reciprocal value ( reciprocal value ) of the focal length applies. With a focal length of 200 mm, an exposure time of 1/200 second or less should be set. With extreme telephoto focal lengths beyond 300 mm, the use of a monopod or tripod is recommended in any case . Particularly heavy lenses have a lens clamp to which the tripod can be attached. Alternatively, lenses and cameras are available that contain an image stabilizer ; this allows the freehand border to be shifted significantly in the direction of longer exposure times.
