Enter the object distance (in) and the focal length (in) into the Image Distance Calculator. The calculator will evaluate and display the Image Distance. 

Image Distance Formula

The following formula is used to calculate the Image Distance. 

1/Di = 1/F - 1/O
  • Where Di is the Image Distance (in)
  • F is the object distance (in) 
  • O is the focal length (in) 

To calculate the image distance, subtract the inverse of the focal length from the inverse of the object distance, then, take the inverse of the result.

How to Calculate Image Distance?

The following example problems outline how to calculate Image Distance.

Example Problem #1:

  1. First, determine the object distance (in). 
    • The object distance (in) is given as: 4.
  2. Next, determine the focal length (in). 
    • The focal length (in) is provided as: 2.
  3. Finally, calculate the Image Distance using the equation above: 

1/Di = 1/F – 1/O

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

1/Di = 1/2 – 1/4 = 4 (in)

Example Problem #2: 

For this problem, the variables needed are provided below:

object distance (in) = 6

focal length (in) = 2

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

1/Di = 1/F – 1/O = ?