Svetosila — the most important characteristic of a lens which in many respects defines quality of the picture. In spite of the fact that this quite difficult optical property, its essence it is quite simple for understanding.
What is svetosit
The photo or video filming is recorded on a photosensitive surface (in a case with digital equipment — on a matrix) light stream passing through a lens. The optics plays a paramount role and its quality in shooting in many respects defines quality of future picture.
Any lens consists of several lenses united in groups. Each of them has the function. Lenses refract light, focusing it on a matrix, protect from distortions, rereflections and other negative optical effects. Passing through these "barriers" the light stream naturally weakens. As a result light which gets on a matrix becomes less bright, grows dull.
There are many ways which help to avoid "light losses" from which the most effective — application of the brightened-up lenses, passing through which, light will lose a minimum of the intensity. And so, the ability of a lens to pass the greatest number of light without loss of intensity and is called svetosily.
How to define a svetosila
Svetosila is a complex concept and its value producers express by means of digital coefficients. So, the simplest, inexpensive a zoom lenses of modern cameras have a svetosila from 3.5 to 5.6 units. The value of coefficient is lower, the svetosila of a lens is higher. Lens Carl Zeiss Planar 50mm f/0.7 created for shooting in space possesses the biggest svetosily. Lenses with high svetosily for shooting on the earth have range from 0.7 to 2.8 units.
Lens Carl Zeiss Planar 50mm f/0.7 was used for shooting of a reverse side of the Moon.
As the svetosila affects quality of shooting
Svetosila defines not only intensity of a light stream that allows to conduct shooting with short excerpts at very weak lighting. It is also connected also with diameter of a relative opening of a diaphragm. The svetosila is higher, the relative opening is wider, so it is less than depth of sharpness. It is especially important in portraiture as by means of such lens it is possible to allocate objects in the foreground and to wash away a background.
The greatest svetosily lenses with the fixed focal length possess.
For this reason a svetosila — the most important characteristic for portrait lenses and any professional photographer-portraitist has high-aperture optics in the arsenal.