T = time

M = magnification

f/ = aperture = lens opening = f/ stop setting of the lens

f/ =         focal length of the lens

        diameter of the opening of the lens

f/ (called “f stop”) is the mathematical function of the lens or ratio of the focal length to the opening of the aperture of the lens.

example: 200mm lens with a 50mm, 25mm or 12.5mm aperture

200/50 = 4 or f/4    200/25 = 8 or f/8    200/12.5 = 16 or f/16

example: 50mm lens with a 25mm or 12.5mm or 8mm aperture

50/25 = 2 or f/2    50/12.5 = 4 or f/4    50/8 = 6.3 or f/6.3

new T =    old T * (M+1)2  

new f/ =   old f/ ÷ (M+1)

new T =    old T * (focal length + extension)2

                     (focal length)2

Reproduction Ratio (magnification) = image size  

                                     subject size

                      ________________________

Reproduction Ratio = √exposure increase factor - 1

with lens mounted in reverse:

new T =     old T * ((focal length * 2) + extension)2

                         (focal length)2