Enter the focal length (mm) and the aperture (mm^2) into the Focal Ratio Calculator. The calculator will evaluate and display the Focal Ratio.
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Focal Ratio Formula
The following formula is used to calculate the Focal Ratio.
FR = FL / A
- Where FR is the Focal Ratio
- FL is the focal length (mm)
- A is the aperture (mm^2)
How to Calculate Focal Ratio?
The following example problems outline how to calculate Focal Ratio.
Example Problem #1:
- First, determine the focal length (mm).
- The focal length (mm) is given as: 5.
- Next, determine the aperture (mm^2).
- The aperture (mm^2) is provided as: 50.
- Finally, calculate the Focal Ratio using the equation above:
FR = FL / A
The values given above are inserted into the equation below and the solution is calculated:
FR = 5 / 50 = .10
Example Problem #2:
For this problem, the variables required are provided below:
focal length (mm) = 6
aperture (mm^2) = 70
Test your knowledge using the equation and check your answer with the calculator above.FR = FL / A = ?
