The Equivalent Aperture Calculator helps photographers, astronomers, and optical engineers determine the diameter of the aperture for a given focal length and f-number. This value indicates the actual physical opening of a lens through which light passes, providing insights into image brightness, exposure, and comparative lens performance. Whether you're comparing different camera systems, telescope setups, or optical sensors, this calculator plays a crucial role in light analysis and imaging control.
Formula of Equivalent Aperture Calculator
1. Based on f-number
Equivalent Aperture Diameter = Focal Length / f-number
This calculates the size of the entrance pupil (aperture opening), giving a clear indication of how much light the system can collect.
2. Relative Aperture (System Comparison)
Relative Equivalent Aperture = √(A₁ / A₂)
Where:
A₁ and A₂ are the respective areas or light-gathering powers of two optical systems. This formula helps compare performance between devices.
3. Telescope Light-Gathering Power
Light-Gathering Power = (D / D₀)²
Where:
D = Diameter of your telescope's aperture
D₀ = Diameter of reference aperture (typically human pupil ~7 mm)
This evaluates how many times more light a telescope can collect compared to the human eye.
Detailed Breakdown of Variables
- Focal Length: This is the distance (in mm or inches) between the lens and the image sensor where the light converges.
- f-number (f/#): The f-number is a ratio that tells you how much light enters the camera. It is dimensionless.
- Aperture Diameter: The actual physical opening that allows light into the system.
- Area Ratios: Used for comparing optical devices; area is proportional to light collection.
- Units: Always use consistent units (mm with mm, inches with inches) for accurate calculations.
Table of General Terms and Reference Values
| Term or Query | Description or Use Case |
|---|---|
| Aperture diameter from f-number | Calculate physical lens opening from f/# and focal length |
| Light-gathering power of telescope | Helps compare telescope performance against the human eye |
| Full-frame vs. crop sensor aperture | Useful when adjusting exposure between camera formats |
| Equivalent aperture for comparison | Comparing brightness or depth of field between lenses or systems |
| How to measure aperture in mm | Uses focal length divided by f-number |
This table helps users quickly find what they need without manual conversions.
Example of Equivalent Aperture Calculator
Scenario:
You are using a camera lens with a focal length of 100 mm and an f-number of 2.8.
Step 1: Apply the formula
Equivalent Aperture Diameter = 100 mm / 2.8 = 35.71 mm
This means the physical size of the aperture is about 35.71 mm, which directly affects light entry and depth of field.
Comparison:
A telescope with a 200 mm aperture will collect significantly more light than one with a 100 mm aperture. Using the light-gathering power formula:
(200 / 100)² = 4
So, the larger telescope gathers four times as much light.
Most Common FAQs
It refers to the actual physical diameter of the lens opening based on focal length and f-number.
Yes, a larger equivalent aperture results in a shallower depth of field.
It helps understand light performance between different cameras or optical systems using different sensor sizes or designs.