Focal length ratio calculator

How to use the calculator

1. Enter the Focal Length (f) of your lens in millimeters (mm). This is the distance from the lens where parallel rays of light converge to a single point.
2. Enter the Lens Length (L) of your lens in millimeters (mm). This is the physical distance from the front vertex of the lens to the back vertex.
3. Click the Calculate button to compute the focal length ratio.
4. The calculator will display the F/L ratio and provide an interpretation of what this value means for lens compactness.

Understanding Focal Length Ratio (F/L Ratio)

The focal length ratio is a critical parameter in optical design that compares the focal length of a lens to its physical length. It is defined as:

F/L Ratio = f / L

Where:

• f = Focal Length of the lens (in mm)
• L = Physical Length of the lens (in mm)

This ratio helps optical designers understand how compact a lens can be while maintaining its designed focal length. A lower ratio (e.g., 0.8) indicates a more compact lens for the same focal length, while a higher ratio (e.g., 1.5) suggests a longer lens that may offer better optical performance but is less compact.

Applications

The focal length ratio is particularly important in:

• Camera lens design and selection
• Telescope construction
• Microscope development
• Mobile device camera systems where space is limited
• Projection systems where lens length constraints exist