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Astronomy & optics

Astrophotography image scale and field of view

Calculate arcseconds per pixel and the horizontal field of view from pixel size, sensor resolution and focal length.

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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

Image scale ≈ 206.265 × pixel size in µm ÷ focal length in mm; field angle = 2 × arctan(sensor width/(2f))

Worked example

Pixels 4 µm wide at a focal length of 800 mm cover approximately 1.0313 arcseconds per pixel near the image centre.

Things to check

  • Image scale uses a small-angle approximation. The full field of view is calculated using arctangent.
  • Account for binning, reducers and Barlow lenses in the effective pixel size or focal length.