Lens calculator - Calculating the effective focal ratio / image brightness

The values of the focal ratio indicated on the lens are normally calculated for an image from the infinite. In case of images from a short distance, particularly macro-images, the effective focal ratio can be calculated which results in the actual image brightness:

k_effective = k * (1 + ß)

The image scale β is calculated from

ß = image size/ object size

Note: Even when using the drop-down lists own values can be entered. Please use the first entry "user def."!

Sensor size :	User def. (mm) 1/4" 3.2 mm 1/3" 4.8 mm 1/2.5" 5.7 mm 1/2" 6.4 mm 1/1.8" 7.2 mm 2/3" 8.8mm 10.5 mm 1" 12.8 mm 1.2" 14.2 mm 15.3 mm 4/3 17.9 mm APS/C 23.7 mm KB 36.0 mm Line .5K 14µm Line 1K 10µm Line 1K 14µm Line 2K 10µm Line 2K 14µm Line 4K 7µm Line 4K 10µm Line 6K 7µm Line 8K 7µm Line 12K 5µm
Set aperture of the lens:	Userdef. f/mm f/1 f/1.4 (1.41) f/2.0 f/2.8 (2.83) f/4 f/5.6 (5.66) f/8.0 f/11 (11.31) f/16 f/22 (22.63)
Object size/ field of view:
Calculated effective aperture:
Effective image brightness in percent compared to selected aperture:

Further details on the function and influence of the aperture can be found in chapter "Aperture of the lens"

The calculated signal intensity must be seen in connection with the general reduction of the image brightness of the respective f-stops: