Fixed focus lens

from Wikipedia, the free encyclopedia

Fixed focus lenses have a fixed focus , i.e. an unchangeable distance setting.

Basic idea

Strictly speaking, lenses only focus on objects in one plane, but you can accept a certain amount of blurring, so that in practice there is a focus area, the depth of field . With a 35mm camera, for example, blur circles of up to 1/30 mm are tolerated. The depth of field depends on the focal length and the aperture value; the shorter the focal length and the higher the aperture value, the greater the depth of field. This can be used for a so-called snapshot setting . For example, if you stop a lens with a focal length of 50 mm to 8 and set the distance to 6 m, the range from 3 m to infinitely sharp is shown. Moving objects can be photographed quickly without being stopped by focusing.

Fixed focus

The idea of ​​the snapshot setting can be used with simple cameras in order to dispense with a distance setting entirely. The conditions are weak lenses, with which an area of ​​about 2.5 m can be covered. This process was already used with the box cameras . Ideally, you support the project with a light wide-angle lens , telephoto lenses, on the other hand, are in principle unsuitable for a fixed focus.

The limit of the light intensity up to which fixed focus lenses can be implemented depends on the film format. With box cameras it is around f / 11, with small picture cameras around f / 9.5 and with 8 mm cine film cameras around f / 2.8.

Use with CCD sensors

CCD sensors are particularly suitable for a fixed focus because they have an extremely small image format. This results in very short focal lengths, which in turn result in a large depth of field. Simple webcams can easily be equipped with a fixed focus lens. However, if you want to penetrate into the macro range, focusing (an autofocus system ) cannot be avoided here either.

Action cams

Action cams, such as those from GoPro, Sony, Rollei have at least predominantly fixed focus lenses with a typically 120 ° –170 ° field of view. It is reported that the "GoPro 3+" camera has a slightly closer focus than previous models.

see also: interchangeable lens , super focus

Individual evidence

  1. video editing-in-action, contribution by Julian, 10 December 2013 at the latest. Accessed 19 June 2015