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Astronomy & optics

Telescope true field of view

Estimate the visible patch of sky from the eyepiece’s apparent field of view and magnification.

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01

Your inputs

The starting values are an example.

Decimals: 12.5 · Thousands: 1,234.56. Follow the field instructions for lists.

02

Your result

Enter your values and select Calculate.

Your calculation will appear here.

Your result will include the relevant values and units.

Understand the calculation

Formula and example

How it is calculated

True field of view ≈ apparent field of view ÷ magnification

Worked example

An eyepiece with a 60° apparent field shows approximately 1.5° of sky at 40× magnification.

Things to check

  • The formula is a practical approximation using the actual magnification.
  • Distortion and the eyepiece’s specific field stop can cause differences.