Фотография. Апертуры и связанные с ними характеристики фотообъективов. Обозначение и измерения
Название (англ.):
Photography - Apertures and related properties pertaining to photographic lenses - Designations and measurements
Описание (англ.):
Pertains to apertures and related properties of photographic lenses affecting the illuminance at the centre of the image. Does apply only to lenses focused on objects at infinity; that is, at least 50 times the focal length of the lens.