The following apply when setting the lens speed:
- Brighter lens luminosity, produces better quality rendering of the resulting images.
- Higher f-numbers indicate smaller apertures, shorter exposure times, and a lower risk of blurred images.
- When increasing the focal length, decrease the lens speed.
- Lowering the lens speed and exposure time under good light conditions, achieves less depth of field.
Methods of expressing luminosity
- F-number: f4 or ranges in Zoom Lenses: F4.0-5.6
- Evaluative number: f1/4 or ranges in Zoom Lenses: f1/4.0-5.6
Quality maximum aperture lenses
- f1.4 for lenses with fixed focal lengths
- f2.8 for zoom lenses with variable focal lengths