Enter the equivalent focal length (mm) into the Calculator. The calculator will evaluate the Shutter Time. 

Shutter Time Formula

ST = 500 / EFL


  • ST is the Shutter Time (seconds)
  • EFL is the equivalent focal length (mm)

To calculate Shutter Time, divide a value of 500 by the equivalent focal length in millimeters.

How to Calculate Shutter Time?

The following steps outline how to calculate the Shutter Time.

  1. First, determine the equivalent focal length (mm). 
  2. Next, gather the formula from above = ST = 500 / EFL.
  3. Finally, calculate the Shutter Time.
  4. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

equivalent focal length (mm) = 20