Auxiliary lens
A conversion lens (also: conversion lens ) is an optical system consisting of one or more lenses that is placed in front of the lens of a camera and changes the focal length or the imaging properties of this lens. Simple ancillary optics that only consist of one lens are called ancillary lens .
Auxiliary lenses are primarily used when a camera does not have the option of using interchangeable lenses of different focal lengths that are suitable for the desired application and can be exchanged. They are usually attached by screwing them into the filter thread of the existing lens or using an adapter . Such auxiliary lenses have largely disappeared in the field of photo cameras, but have been experiencing a renaissance in compact digital cameras since the late 1990s.
In amateur video cameras, attachment lenses are widespread, especially for the wide-angle range, since these do not have interchangeable lenses. Usual screw-in threads in this area have a diameter of 25, 37 and 58 mm.
Typical attachment adapters are:
- Wide-angle attachment to enlarge the angle of view , focal length factor about 0.3 to 0.8, partly with fish-eye effect . Wide-angle attachments can usually be used with any focal length setting of a basic zoom lens.
- Tele-converter to reduce the angle of view, focal length factor around 1.5 to 3. Tele-converter can usually only be used with the longest set focal length, settings in the wide-angle range of the zoom lens lead to strong vignetting .
- Anamorphic attachment , for anamorphic recording
Suppliers are, for example, Century Precision Optics (belongs to Schneider Optics ), Raynox (a brand of Yoshida Industry Co., Ltd. , Tokyo ), Digital King (a brand of the Japanese Toda-Seiko Co., Ltd ), Kenko (Japan), Hama and the camera manufacturers themselves.
Macro attachments and close-up lenses also change the focal length of the basic lens, but serve exclusively to reduce the possible distance between the camera and the subject in order to enable a picture with a larger image scale. Close-up lenses are also used in single-lens reflex cameras.
Other meanings
Some older cameras were equipped with so-called set lenses, which are sometimes also referred to as attachment lenses, in which a basic lens and the shutter were permanently mounted and the focal length could be adjusted using system-specific attachments. Because of the considerable limitations compared to real interchangeable lenses, this technology has not established itself permanently despite the lower costs.