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Telescope Magnification and Exit Pupil Calculator — result sheet
Calculate visual telescope magnification, exit pupil, and focal ratio from objective and eyepiece dimensions.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Magnification=objective focal length÷eyepiece focal length; exit pupil=objective aperture÷magnification; focal ratio=objective focal length÷objective aperture.
The page treats a telescope and eyepiece as an ideal afocal visual combination. A longer objective focal length or shorter eyepiece focal length increases the angular magnification, while aperture divided by magnification gives the ideal exit-pupil diameter in the same length unit.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Objective focal length — mm; minimum 1.0E-6; maximum 1000000000
- Eyepiece focal length — mm; minimum 1.0E-6; maximum 1000000000
- Objective aperture — mm; minimum 1.0E-6; maximum 1000000000
Worked example
| Input | Value |
|---|---|
| Objective focal length | 1200 |
| Eyepiece focal length | 25 |
| Objective aperture | 200 |
Magnification = 48×; exit pupil ≈ 4.167 mm; focal ratio = f/6.
Assumptions and limits
- The objective and eyepiece focal lengths and aperture are positive and expressed in millimetres.
- Magnification is the ideal absolute visual ratio; an astronomical refractor or reflector may produce an inverted image without changing the magnitude shown.
- The exit pupil is an optical diameter estimate and is not a guarantee that every observer can use the full beam.
- Atmospheric seeing, optical quality, obstruction, field stop, eye relief, tracking, and a manufacturer’s usable-power guidance are not modeled.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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