23.5 × 15.7 mm sensor at 480 mm
The ideal rectangular field is approximately 2.8045° wide by 1.8739° high. These are synthetic dimensions, not a tested equipment pairing.
Load this example in the calculatorTelescope field-of-view calculator
Estimate rectangular camera field width and height from sensor dimensions and effective focal length.
The interactive calculator loads in your browser. Without JavaScript, the method and worked examples below remain available.
What this calculation tells you
Field of view answers how much angular sky fits across a sensor, not how sharply the corners will image. Use the sensor’s active width and height in millimetres; a marketing sensor-format label is not a measurement.
Inputs and workflow
- Enter the effective focal length after any optical reducer or amplifier, in millimetres.
- Enter active sensor width and height in millimetres, not pixel counts.
- Compare each angular dimension with the target, then check rotation and framing against a sky survey or a plate-solved image.
Formula and units
Field (degrees) = 2 × atan(sensor dimension / (2 × focal length)) × 180 / π. Calculate width and height separately.
Worked examples
Same sensor at 960 mm
Doubling focal length reduces both field dimensions to about half: approximately 1.4025° × 0.9370°. It does not change the sensor’s physical dimensions.
Load this example in the calculatorLimits before using the result
The formula assumes an ideal rectilinear projection. Optical distortion, usable image circle, cropping, rotation and pointing uncertainty are not modeled.
A target fitting the rectangle does not establish edge illumination or mechanical compatibility. Leave a practical framing allowance and inspect actual capture geometry.
Sources and method notes
- NINA: framing assistant
Documents sky-survey framing and plate-solved image workflows. The equation above is our ideal geometric derivation, not a reproduction of NINA’s implementation.
Calculation notes maintained by AstroGearFit. Updated September 7, 2026. Examples are numerical demonstrations, not hands-on equipment tests. The method notes are currently in English; the existing interface language selector remains available.
Choose a calculation
Five focused checks with reproducible examples and explicit limits. These tools do not certify a complete equipment combination.
- Back-focus spacing calculator
Calculate whether your imaging train is too short, matched numerically, or too long for the specified sensor distance.
- Telescope field-of-view calculator
Estimate rectangular camera field width and height from sensor dimensions and effective focal length.
- Pixel-scale calculator
Convert camera pixel pitch and telescope effective focal length to angular image scale in arcseconds per pixel.
- Seeing and pixel-sampling calculator
Express an entered seeing FWHM in pixels using your camera pitch and effective focal length, without an automatic good/bad verdict.
- Mount payload comparison calculator
Compare a declared carried mass with the manufacturer rating for the exact mount configuration and identify an excess explicitly.
Filter sizing is paused. Whole-system compatibility needs verified interfaces, optical specifications and configuration-specific evidence.