Interactive Aperture Area Calculator
How to Use This Calculator
This calculator determines the light-collecting area of a circular aperture, such as a telescope lens or mirror. It can also account for a central obstruction (e.g., a secondary mirror).
- Enter the diameter of the main aperture (Dap). Choose the appropriate units (mm, cm, m, inches).
- Optionally, enter the diameter of the central obstruction (Dobs). Choose its units. If there's no obstruction, you can leave this blank or enter 0.
- Click the "Calculate Aperture Area" button.
- The results (total area, obstruction area, effective area) and a step-by-step solution will be displayed below.
Theory: Aperture Area & Central Obstructions
The aperture area of an optical instrument is the primary factor determining its light-gathering power. A larger area collects more photons, resulting in brighter images and the ability to see fainter objects.
Many reflecting telescopes (e.g., Newtonian, Cassegrain, Schmidt-Cassegrain) have a central obstruction caused by a secondary mirror or other components in the light path. This obstruction blocks a portion of the incoming light, reducing the effective light-collecting area.
The effective area is the total area of the main aperture minus the area of the central obstruction. This net area is what actually contributes to forming the image. While central obstructions reduce light grasp, they can also affect image contrast and diffraction patterns.
Formulas Used
- 1. Area of a Circle (A):
A = π × r2 = π × (D/2)2 = (π/4) × D2A= Areaπ(pi) ≈ 3.14159r= Radius of the circleD= Diameter of the circle
- 2. Total Aperture Area (Aap): Calculated using the main aperture diameter (Dap).
- 3. Obstruction Area (Aobs): Calculated using the obstruction diameter (Dobs). If Dobs is 0, Aobs is 0.
- 4. Effective Collecting Area (Aeff):
Aeff = Aap - Aobs