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THE FEUTEX TOOLKIT

Telescope Eyepiece Performance

Compare eyepiece magnification, exit pupil and approximate true field of view.

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01 Your input
02 Your result
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FormulaMagnification = f/e; Exit pupil = d*e/f; Approximate true field = a*e/f
Sources and model references

Worked example

Inputs

Telescope focal length
1000 mm
Eyepiece focal length
25 mm
Aperture
200 mm
Apparent field
60 degrees

Expected results

Magnification
40 ×
Exit pupil
5 mm
Approximate true field
1.5 degrees

Load the example in the workspace to reproduce these results. Display rounding does not change the underlying calculation.

How to use this tool

  1. Compare eyepiece magnification, exit pupil and approximate true field of view.
  2. Set telescope focal length, eyepiece focal length, aperture, apparent field in the indicated units.
  3. Calculate and compare magnification, exit pupil, approximate true field.

Try this example

{
  "f": 1000,
  "e": 25,
  "d": 200,
  "a": 60
}

Accuracy and scope

Idealized educational model. Enter measured values in the displayed units; real systems may require additional corrections.

Is my data uploaded?

This tool runs locally in your browser. Input and output are not sent to a processing server. Copy or download your result before leaving the page.