How to Use This Calculator
- Enter the focal length (in mm) for each lens in your camera system. If your camera has a single lens, enter that lens's focal length.
- Enter the aperture (f-stop) value for each corresponding lens. This can be the lens's native aperture or the aperture you'll be shooting at.
- Click the "Calculate" button to compute the effective focal length of your lens system.
- The calculator will display the effective focal length in millimeters (mm).
Understanding Effective Focal Length
Effective Focal Length (EFL) represents the total magnifying power of a camera lens system, taking into account the focal lengths and apertures of each individual lens. It's particularly important when using multiple lenses, such as with teleconverters, extension tubes, or when calculating the combined effect of multiple lens elements in a complex system.
Practical Applications
- Calculating Field of View: EFL directly affects the field of view of your camera, with longer effective focal lengths producing narrower fields of view (zoom effect).
- Depth of Field Estimation: Understanding EFL helps in estimating the depth of field for different lens configurations.
- Photography Planning: Useful when planning multi-lens setups for specific creative effects or technical requirements.
Example
If you're using a 50mm f/1.8 lens with a 2x teleconverter (which typically adds approximately 1 stop of light loss), you would:
- Enter 50mm for the first lens's focal length and f/1.8 for its aperture.
- Enter 100mm (50mm × 2) for the teleconverter's focal length and f/2.8 (f/1.8 × √2 ≈ f/2.8) for its effective aperture.
- Click "Calculate" to get the effective focal length of your system.