Enter the focal length (mm) and the distance between nodal points (mm) into the Minimum Focus Distance Calculator. The calculator will evaluate and display the Minimum Focus Distance. 

Minimum Focus Distance Formula

The following formula is used to calculate the Minimum Focus Distance. 

MFD = FL * 4 + DN
  • Where MFD is the Minimum Focus Distance (mm)
  • FL is the focal length (mm) 
  • DN is the distance between nodal points (mm) 

To calculate the minimum focus distance, multiply the focal length by 4, then add the distance between modal points.

How to Calculate Minimum Focus Distance?

The following example problems outline how to calculate Minimum Focus Distance.

Example Problem #1:

  1. First, determine the focal length (mm).
    • The focal length (mm) is given as: 3.25.
  2. Next, determine the distance between nodal points (mm).
    • The distance between nodal points (mm) is provided as: 5.
  3. Finally, calculate the Minimum Focus Distance using the equation above: 

MFD = FL * 4 + DN

The values given above are inserted into the equation below and the solution is calculated:

MFD = 3.25 * 4 + 17 = (mm)

Example Problem #2: 

For this problem, the variables needed are provided below:

focal length (mm) = 7

distance between nodal points (mm) = 5.5

This example problem is a test of your knowledge on the subject. Use the calculator above to check your answer. 

MFD = FL * 4 + DN = ?