Telescope Light Gathering Calculator Formula
Understand the math behind the telescope light gathering calculator. Each variable explained with a worked example.
Formulas Used
Light Gathering Power
lgp = pow(aperture / eye_pupil, 2)Collecting Area
area_cm2 = pi * pow(aperture / 20, 2)Variables
| Variable | Description | Default |
|---|---|---|
aperture | Telescope Aperture(mm) | 200 |
eye_pupil | Eye Pupil Diameter(mm) | 7 |
How It Works
Light Gathering Power
LGP = (D_telescope / D_eye)²
Light collection scales with the area of the aperture. A 200 mm scope collects (200/7)² ≈ 816 times more light than the dark-adapted eye (7 mm pupil).
This is why larger telescopes see fainter objects.
Worked Example
A 200 mm telescope vs 7 mm pupil.
aperture = 200eye_pupil = 7
- 01LGP = (200/7)² = 28.57² = 816×
- 02The scope gathers 816 times as much light.
- 03Area = π × (200/20)² = π × 100 = 314 cm²
Ready to run the numbers?
Open Telescope Light Gathering Calculator