Floating elements

Floating elements (such as: floating elements ) are a means for the correction of aberration of a lens at the set distance match. This is done by changing the axial distance between the lenses .

Floating elements were introduced in the 1970s and are often used in high - quality, high -speed wide - angle lenses . This technique is also known as floating focusing or (automatic) correction compensation . The term automatic here means that the adjustment of the lens distance is linked to the distance setting so that the correct correction is always obtained.

The distance setting takes place with conventional lenses, mostly by the fact that the entire lens is axially displaced, without changing the spacing of the lenses, as this is the simplest mechanically on. The correction of the aberrations is normally done for an infinite distance of the object to be imaged. If the distance is smaller, the beam path changes in such a way that the aberrations increase. This problem is most pronounced with fast, wide-angle lenses. On the other hand, if the correction is carried out as a compromise for all adjustable distances, then the image quality at infinity will accordingly be somewhat worse. This can be counteracted by moving two (rarely more) lens groups independently of one another when focusing. This results in additional degrees of freedom for the correction so that the various distances can be better dealt with.

It is also advantageous that the maximum imaging scale can be larger, since the imaging errors no longer increase so much at shorter distances. The disadvantage, of course, is the greater mechanical effort. The mechanics that move the lenses against each other must work particularly precisely so that the lenses are not too decentered (shifted sideways or tilted against each other). This would seriously disrupt the correction of the aberrations.