Wide angle lens
The natural perspective perception of humans is most closely matched by lenses with an angle of about 40 to 50 °, the so-called normal lenses . In contrast, the wide-angle lens has a shorter focal length and a larger angle of view. Objects that are far away are shown smaller, so a wide angle reduces the image scale for the same subject distance. In practice, this also results in the large depth of field that is characteristic of wide-angle photos . A wide-angle lens thus has the opposite properties of the telephoto lens . The wide-angle lenses also include fisheye lenses .
Wide-angle lenses, in particular very bright ones, require a high level of structural effort ( retrofocus ) for single-lens reflex cameras , since space for the mirror in the area of the focal length must be kept free. Lenses for adjustable technical cameras are often designed as wide-angle lenses because of the large image circle required for this application , even if the focal length is in the range of normal lenses.
Focal lengths and angles of view
- for comparison: normal focal length
- This corresponds to a lens with a focal length of 45 mm to 60 mm for the 35 mm format, and 75 to 85 mm for the medium format 6x6 cm . With smaller film formats or smaller sensor sizes in digital cameras , the normal focal length is reduced accordingly.
The wide-angle focal lengths are below the normal focal lengths. In medium format photography and in large format, the wide-angle focal lengths are larger than in the 35 mm format used for comparison, in accordance with the larger film format. For smaller image formats, for example for smaller digital sensors, for half-format or narrow-film cameras, there is a correspondingly smaller focal length for the same angle of view.
Wide-angle lenses are offered as lenses with a fixed focal length, but also as zoom lenses that allow the focal length to be adjusted. Different class names are common for wide-angle lenses, depending on the focal length and the typical purpose.
Moderate wide-angle lenses (reportage lenses)
Reportage lenses are wide-angle lenses with a so-called light to medium wide-angle effect, which occurs at a diagonal angle of view between 60 ° and 75 ° and a focal length of between around 28 mm and 38 mm in relation to a small image. Due to the greater depth of field and the still relatively low distortion, they are often used for reportage photography . Typical reportage focal lengths are also covered by most inexpensive wide-angle lenses and universal zooms. In this focal length range, there are also lenses with very high light intensities for analog and digital SLR cameras .
The following are considered to be moderate wide-angle focal lengths (based on 35mm format)
- 35 mm (diagonal angle of view 63 °).
- 28 mm (diagonal angle of view 75 °).
Super wide angle lenses
Lenses with diagonal image angles of at least 90 ° are called super wide-angle lenses. Super wide angle lenses are also known as ultra wide angle lenses. The usual abbreviations are therefore SWW and UWW. Such lenses are specifically used, for example, in artistic photography and nature photography , but occasionally also in nude photography , in order to achieve spectacular effects through the perspective distortions typical of these angles of view. The super wide-angle lens with the largest image angle, which images with relatively little distortion and halfway sharp, is the Hypergon , which can illuminate a diagonal image angle of 135 ° on a large-format photo plate.
Typical super wide-angle focal lengths for the 35mm format are:
- 21 mm (diagonal angle of view 92 °)
- 20 mm (diagonal angle of view 94 °)
- 18 mm (diagonal angle of view 100 °)
- 17 mm (diagonal angle of view 104 °)
- 14 mm (diagonal angle of view 114 °)
- 12 mm (diagonal angle of view 122 °)
Zoom lenses with wide angle range
Zoom lenses ("rubber lenses" according to old parlance) have a variable angle of view, which can also include wide-angle imaging; then one speaks of a “telephoto wide-angle zoom” or a “transition zoom”. In the past, the special optical conditions ensured that zoom lenses for the wide-angle range came onto the market much more hesitantly than telephoto zoom - the imaging errors are considerably more difficult to correct here than with long focal lengths. Today, however, these errors can be kept within limits with computer-aided design and innovative special glasses.
Transitional zooms began in the 1970s with areas of 35–70 mm, from a slight wide angle to portrait focal lengths beyond the normal focal lengths, but have developed enormously from this. Examples today are the so-called “travel zooms” with focal lengths of 28–200 mm, that is, from moderate wide-angle to telephoto focal lengths.
In critical shooting situations, for example in architectural photography, fixed focal lengths still have advantages. In particular, the so-called super zoom lenses , which cover a very large focal length range, often show drastic imaging errors at the short end, in particular distortion and edge blurring.
In the other case, the variable image angles of a zoom only include wide-angle focal lengths: This is called a wide-angle zoom.
Typical wide-angle zoom lenses for the 35mm format are:
- 24–70 mm (diagonal angle of view 83 ° –34 °),
- 17–40 mm (diagonal angle of view 104 ° –57 °),
- 16–35 mm (diagonal angle of view 107 ° –63 °) and
- 12–24 mm (diagonal angle of view 122 ° –83 °).
From fish-eye lens (Engl. Fisheye lens ) occurs at focal lengths below 20 then mm when they intentionally have a strong barrel distortion, so straight lines bend the stronger the farther they extend from the center of the image removed (see figure). A fisheye that captures the diagonal corners at an angle of view of 180 degrees has a focal length of 16 mm. A fisheye that images 180 degrees on the smallest side only has a focal length of 8 mm. The image is then circular in the center with black remaining areas. In contrast to super wide-angle lenses, a fisheye lens has a different type of projection:
- Straight lines that do not go through the center of the image are bent outwards.
- Solid angles are displayed less distorted than with super wide-angle lenses.
- Image angles of 180 ° and more are possible, which is geometrically impossible with rectified wide-angle lenses.
- Objects at the edge of the picture are indeed curved, but in contrast to the super wide angle, they are not shown stretched in width - in this respect a fisheye depicts “more correctly” than a wide angle.
A fisheye lens has two main characteristics:
- The focal length: The focal length determines the image scale. In the center of the image, the fisheye lens and the super wide-angle lens have the same magnification with the same focal length. In the fisheye it is constant over the field of view, in the wide angle it increases outwards.
- The angular range shown by the optics (typically 150 ° to 180 °, exceptions up to 250 °)
Depending on the sensor or light-sensitive film surface used, the following cases of coverage between the optics and the recording surface can occur:
- The sensor is completely exposed by the lens (normal rectangular image). This is the case with sensors in 35mm image size and 180 ° image angle from a focal length of 14 mm.
- The sensor is partially exposed by the lens, at the same time light also passes the sensor. For sensors in 35mm image size and 180 ° image angle, this is the case between 8 mm and 13.5 mm focal length.
- All the light coming from the optics lands on the sensor (round, circular image). This is the case with sensors in small picture size and 180 ° image angle up to a focal length of 8 mm.
Typical fisheye lenses for the 35mm format are:
- 16 mm (diagonal angle of view 180 °)
- 7.5 mm or 8 mm (round picture)
An exotic is the Nikkor with 6 mm focal length and 220 ° angle of view, in different versions on the market since the 1960s, which also creates a round image, but can look a little bit “backwards”.
Fish-eye zoom lenses
In 1995, Pentax launched a fisheye lens with a variable focal length from 17 to 28 mm for the 35mm format, which was produced until 2004. In cooperation with Tokina , this lens found a successor for digital SLR cameras with crop sensors in 2006 with the 10-17mm / f 1: 3.5-4.5.
In 2011 Canon brought out the "EF8-15mm f / 4L Fisheye USM" zoom lens, which can zoom from a round image (8 mm) to a rectangular image (15 mm) on cameras with sensors in 35mm format. For sensors in APS-C and APS-H format, it has the marks C (10 mm) and H (approx. 12 mm) for the rectangular image. An uncut round picture is then not possible.
When zooming, the typical fish-eye image with barrel-shaped distortion remains. Even with the longer focal length, these lenses do not behave like the corresponding wide-angle lenses.
The wide-angle lens on the camera
General construction problems
Wide-angle lenses can be attached to suitable system cameras as interchangeable lenses or are permanently integrated into them. Because of the great depth of field, inexpensive cameras often have a fixed focus lens in the (moderate) wide-angle range.
The construction of wide-angle focal lengths for single-lens reflex cameras is not easy, since the oscillation area for the mirror must be kept free at a depth of approx. 40 mm in front of the film, and so so-called " retrofocus " constructions are necessary for this reason . These artificially relocate the focal point without distorting and vignetting . This design makes the construction more complex, the lenses are larger, heavier and more expensive.
Some special constructions that were not made in retrofocus could only be used on SLR cameras whose mirrors could be locked manually. A clip-on viewfinder was then used because the viewfinder mirror could not be used.
In addition, these constructions only have a very narrow geometrically axial distance setting range. In large-format cameras with distance adjustment of the lens standard over the floor or over the optical bench, so-called wide - angle adjustment devices are used because of the close proximity of the rear lens element to the film plane .
Wide-angle conversion lenses and converters
Wide-angle converters are also available which, when screwed in front of a lens, enlarge the lens' angle of view. Usual multipliers of the focal length are between 0.3 and 0.8, sometimes with a fish-eye effect . Such a converter with a factor of 0.8 shortens, for example, a 28 mm wide-angle lens for 35 mm cameras to a focal length of about 22 mm and increases the diagonal angle of view from 75 ° to about 90 °.
Occasionally, instead of the shortening of the focal length, the multiplier of the areas shown is given, which describes the same effect with a numerical value that deviates more from one (lower numerical value for wide-angle converters). The “normal” multiplier of the focal length then results as the square root of the area factor .
In order to keep the unavoidable compromises in image quality small, such attachments must be specially designed for the system in question. In the case of universal wide-angle attachments that are not specifically designed for a specific camera or lens, image errors occur such as strong distortions, edge shading or color fringes due to chromatic aberrations .
Like most lens attachments, wide-angle converters are also supplied with standardized screw-in threads. For digital compact cameras without filter threads, very complex adapter brackets ("filter adapters") are often required for assembly.
Image circle larger than film format
In photography with view cameras, wide-angle lenses are sometimes used to describe all those lenses that have the largest possible image circle , beyond the requirements of the film format. This larger image circle allows extensive adjustments of the lens on the camera, e.g. B. Axis shifts (" shift lenses " for the distortion-free representation of buildings).
Furthermore, the angles of the optical axes (" tilt lenses "), which also require a larger image circle.
- HAL 250. Entaniya Co., Ltd., Accessed February 16, 2018 .
- EF 8-15mm f / 4L Fisheye USM - Manuals. Canon Germany, accessed October 8, 2014 .
- Lumix Forum: Wide-angle attachment lens for GX7 with Pana 20 / Oly 12-50. July 19, 2015, accessed August 7, 2016 .