Open aperture

The open aperture is a numerical value that denotes the largest possible aperture of a lens .

It is not the diameter of the aperture that is given, but the aperture ratio , e.g. B. 1: 2.8, often also written as f: 2.8 or f / 2.8 , to emphasize the dependence on the focal length of the lens.

Taking photos with an open aperture has several effects:

The open aperture affects images created with it in such a way that the depth of field is as small as possible for a given lens and recording format. This design means is z. B. often used in portrait photography to distinguish the depicted person from the then blurred background and to draw the viewer's attention to the person.
When the aperture is open, lens defects are most apparent. In particular, images created with an open aperture often suffer from vignetting , lack of contrast and reduced general sharpness . With most lenses, the image quality improves noticeably with moderate stopping down , but the sharpness deteriorates again at very small aperture settings due to diffraction effects .