F factor conversion

Owned by Onno Verkerk
Sept 30, 2020
1 min read

<-- less light

 

more light -->

F2

F1.8

F1.6

F1.4

F1.2

F1.1

F1

z

 

 

2z

 

 

4z

 

(1+1/3)z = (4/3)z

(1+2/3)z = (5/3)z

 

(1+1/3)2z = (8/3)z

(1+2/3)2z = (10/3)z

 

 

 

 

 

 

 

 

y

(3/4)y

(3/5)y

(1/2)y

(3/8)y

(3/10)y

(1/4)y

 

F1 passes 100% more light than F1.4 and F1.4 passes 100% more light than F2. This means that a factor of 2 can be used in light intensity from F2 to F1.4 and from F1.4 to F1; or a factor of 4 from F2 to F1.
F1.8 passes 1/3 more light than F2, and F1.6 passes 2/3 more light than F2.
F1.2 passes 1/3 more light than F1.4, and F1.1 passes 2/3 more light than F1.4.

We are talking about the light that passes to the sensor depending of the F factor. 

But we can also think about the minimum illumination parameter and use the same principles: if at F1 passes 100% more light than F1.4 means that the minimum light required at F1 would be half than F1.4.
The line in green in the table indicates this.

Example:             Min illumination at F1.6 = 0.04 lux

                                I will calculate it for F1.2

F1.6 = (3/5)y = 0.04 à y = 0.066 lux         à the min illumination at F2 is higher than F1.6 (which makes sense)

F1.2 = (3/8)y = (3/8) * 0.066 = 0.024 lux à the min illumination at F1.2 is lower then F1.6