In photography, normal lenses are lenses with a focal length that roughly corresponds to the diagonal of the picture format ( normal focal length ). This results in a mathematical image angle of around 53 degrees , regardless of the recording format , but in most cases the image angle used is somewhat smaller and lies in the range between 40 and 50 degrees.
Lenses with a shorter focal length (and a larger angle of view) than normal lenses are called wide-angle lenses , lenses with a longer focal length (and smaller angle of view) as long-range or telephoto lenses .
Before zoom lenses became widespread , SLR cameras were mostly sold together with a normal lens . Due to the high number of items and the uncomplicated, optically often almost symmetrical construction, normal lenses are the cheapest, bright lenses with mostly excellent imaging properties.
Common normal lenses for the 35mm format almost always have initial apertures of 1: 1.8 to 1: 1.4, for the medium formats 1: 2.8 to 1: 1.9. Other focal lengths that are so bright are much more complex to build (larger lenses required) and much more expensive. There are normal lenses for the 35mm format with initial apertures of 1: 1.2 or even 1: 0.95.
With today's standard division of fixed focal lengths , normal lenses are the lenses with the shortest focal length, which do not require a retrofocus construction in " single -lens" SLR cameras . With these cameras, shorter focal lengths require additional lenses in order to create enough space for the oscillating mirror behind the lens, which increases the cost of design, optical correction and manufacture.
A focal length of 50 mm has established itself in practice for single-lens reflex cameras for the 35 mm format, although the diagonal of the recording format (24 mm × 36 mm) is only 43.3 mm. Individual manufacturers also referred to lenses with a focal length of 55 mm to 60 mm as normal lenses . In contrast, compact 35mm cameras with permanently mounted lenses often have shorter focal lengths between about 38 mm and 45 mm.
In the case of medium format cameras with a recording format of 6 cm × 6 cm, the normal focal length is approximately 80 mm. In the case of the 6 × 9 cm roll film format that was frequently used in the past , 100 mm is the normal focal length.
With large format cameras , which are available from 4 "× 5" image formats up to 8 × 10 "( inches ), for example , the relationship becomes clear: a normal lens for the image format 6 cm × 9 cm (image diagonal = 10.8 cm ) with a focal length of 105 mm would be more of a light wide-angle lens for the next larger format 9 cm × 12 cm (image diagonal = 15.0 cm) .
In digital cameras , regardless of the pixels , the size of the photosensitive number, corresponding to the sensor surface (see form factor ). With the Four Thirds standard for digital SLR cameras, the active sensor diagonal is just under 22 mm; the normal focal length here is 25 mm. With APS-C format (sensor diagonal approx. 28 mm) the normal focal length corresponds to approx. 30 mm.
- Normal lens in olypedia.de