Focal Length Calculator
Calculate focal length, magnification, angle of view, and field of view for photography and optics
Lens Parameters (Enter at least 3 values)
Real size of the object being photographed
Camera sensor or film diagonal measurement
Distance from lens front to the object
Ratio of image size to object size
Distance from lens center to focal point
Angular width of the field of view
Enter at least 3 values to calculate the results
The calculator needs sufficient information to determine the remaining parameters
Example Calculation
Portrait Photography Example
Scenario: Photographing a person 2m tall from 10m distance
Object size: 200 cm (2 meters)
Object distance: 10 m
Sensor: Full frame (43.3mm diagonal)
Desired focal length: 85mm
Calculated Results
Magnification: ~0.022× (2.2%)
Angle of view: ~28.6°
Field of view: ~5.3m wide at 10m distance
This shows how a telephoto lens compresses the scene and provides a narrow field of view
Focal Length Categories
Ultra Wide (8-24mm)
Extreme wide angle, distortion effects
Wide Angle (24-35mm)
Landscape, architecture photography
Standard (35-85mm)
Natural perspective, general use
Telephoto (85-200mm)
Portraits, wildlife, sports
Super Telephoto (200mm+)
Extreme magnification, compression
Common Sensor Sizes
Photography Tips
Longer focal lengths compress perspective and increase magnification
Wider angles capture more of the scene but with lower magnification
Magnification depends on both focal length and subject distance
Use longer focal lengths for subject isolation and background blur
Understanding Focal Length and Lens Optics
What is Focal Length?
Focal length is the distance between the lens's optical center and the image sensor when the lens is focused at infinity. It's measured in millimeters and determines how much of the scene will be captured and how large objects will appear in the image.
Key Relationships
- •Magnification: How large the image appears relative to the object
- •Angle of View: How much of the scene is captured
- •Field of View: The actual area visible at a given distance
- •Perspective: How spatial relationships appear
Essential Formulas
Thin Lens Equation:
1/f = 1/d₀ + 1/dᵢ
Magnification:
M = Image Size / Object Size
Angle of View:
θ = 2 × arctan(sensor / (2 × f))
Variables
- f: Focal length (mm)
- d₀: Object distance (m)
- dᵢ: Image distance (m)
- M: Magnification factor
- θ: Angle of view (degrees)
Practical Applications
Understanding focal length relationships helps photographers choose the right lens for their needs. The calculator helps determine how different focal lengths will affect composition, magnification, and field of view for any given shooting situation.
Portrait Photography
• 85-135mm focal lengths
• Flattering perspective
• Background compression
Landscape Photography
• 14-35mm focal lengths
• Wide field of view
• Maximum scene capture
Wildlife Photography
• 200-600mm focal lengths
• High magnification
• Subject isolation