f number
- noun
- /ɛf ˈnʌmbər/
- Specialized
:
número f
- When adjusting the exposure, it's important to consider the f number of the lens being used.
Examples
-
So, So what you really want to do is compare the F number of your optics for collecting simple fluorescence and the F number of the monochromometer.
-
The photographer chose a low f number to achieve a wide aperture and let in more light.
-
OK, so generally large numerical aperture is good or equivalently low F number is good provided you can afford it of course.
-
A lower f number results in a shallower depth of field, making the background blurry.
Synonyms
72
8.5
How much light a camera lens lets in
1
7.8
A number showing how bright an image is, found by dividing focal length by lens diameter
A number that shows how wide a camera lens opens to let light in
Surface Forms
Morphology
f + number
This is a specialized photographic term: the meaning (ratio of focal length to aperture) is technical and cannot be inferred from knowing 'f' (a letter/abbreviation with no general lexical meaning) and the generic word 'number'. A B1 learner who knows the constituents but lacks photography-domain knowledge would not predict this sense, so the expression is effectively idiomatic/technical rather than compositional.
Etymology
F number comes from the letter f for 'focal' and the word number, because it compares the lens's focal length to the size of its front opening. A small f number means a wide opening that lets in more light, and a large f number means a small opening that lets in less light.