| Subject | English | German |
| transp., energ.ind. | F2 octane number | Motoroctanzahl |
| transp., energ.ind. | F2 octane number | F2-Octanzahl |
| comp., MS | f-number | Blendenzahl (In photography, the diameter of the aperture expressed in terms of the focal length of the camera lens. The greater the f-number, the less light reaches the film and the more in focus the objects in the foreground and the background will be. For example, with an f-number = 16 the objects in the far background will be in focus. Whereas, with an f-number = 2 the background will be blurry (while foreground objects are in focus)) |
| opt. | f-number | relative Öffnung (it is a measure of the light-gathering ability of a lens) |
| opt. | f-number | Blendengröße |
| opt. | f-number | Blendenwert |
| opt. | f-number | Öffnungszahl (a measure of the light-gathering power of the aperture; the ratio of the focal length to the diameter of the largest entering parallel beam that can pass through the lens) |
| opt. | f-number | Öffnungsverhältnis (if is a measure of the light-gathering ability of a lens) |
| opt. | f-number | Blendennummer |
| opt. | f-number | Blende |
| astr. | f-number | Blendenzahl |
| microel. | f-number of the projection optics | Blendenzahl der Projektionsoptik (optische Projektionslithografie) |
| microel. | f-number of the projection optics | Blende der Projektionsoptik (optische Projektionslithografie) |
| chem. | the scum contained a considerable number of sulphate ions but no chloride ions %1F De Vries | der Schlamm enthielt groessere Mengen an sulfationen, dagegen keine Chloridionen |