Fixed focus lens
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
- ↑ http://videobaschineung-in-action.de/entscheidungshilfe-gopro-hero-3-ja-oder-nein/ video editing-in-action, contribution by Julian, 10 December 2013 at the latest. Accessed 19 June 2015