Effective Focal Length


The concept of effective focal length (EFL) is crucial for photographers, filmmakers, and optical engineers. EFL determines how a lens will perform in terms of magnification and field of view. Understanding how to calculate EFL allows users to make informed decisions about lens selection and use.

How to Use the Calculator

Using the effective focal length calculator is straightforward. Simply input the necessary parameters, such as the focal length of the lens and the crop factor of the camera sensor. Then, click the “Calculate” button to get the effective focal length.


The formula to calculate the effective focal length is:

EFL=Focal Length×Crop Factor


  • Focal Length is the lens focal length in millimeters.
  • Crop Factor is a multiplier that accounts for the difference in sensor size compared to a full-frame sensor.

Example Solve

Let’s assume we have a lens with a focal length of 50mm and a camera with a crop factor of 1.5.

Using the formula:

EFL=50 mm×1.5=75 mm

So, the effective focal length is 75mm.

Frequently Asked Questions

What is the crop factor?

The crop factor is a ratio that compares the size of a camera’s sensor to a full-frame sensor. It adjusts the focal length to account for the sensor size.

Why is effective focal length important?

EFL helps photographers understand how a lens will behave on different camera bodies, particularly those with smaller sensors.

How does sensor size affect focal length?

Smaller sensors crop the image, effectively increasing the focal length, hence the term “effective focal length.”

Can I use this calculator for all types of lenses?

Yes, this calculator works for any lens as long as you know the focal length and the crop factor.

Is the effective focal length the same as the actual focal length?

No, the effective focal length adjusts the actual focal length based on the sensor size, giving a more accurate representation of how the lens will perform.


Understanding effective focal length is essential for optimizing your photography and videography. By using the EFL calculator, you can quickly determine how different lenses will perform on your camera, ensuring you get the perfect shot every time.

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