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Astronomy Calculators

Put your telescope, eyepiece, and camera specifications to work. Calculate visual magnification and field of view, or plan camera framing and pixel scale for astrophotography.

Eyepiece calculator · Astrophotography calculator

For explanations and worked examples, read Magnification and Field of View and Telescope Focal Ratios. Explore the Astrophotography gallery for image stories and capture details.

Telescope and eyepiece calculator

Enter the specifications printed on your telescope and eyepiece. All lengths are in millimeters. For inches, multiply by 25.4. The values below are an example; replace them with your own.

Use 1 for no accessory, 2 for a 2× Barlow, or 0.63 for a 0.63× reducer. Actual factors can vary with spacing.

Enter your specifications and select Calculate.

True field is an estimate, not a guarantee of an unobstructed view. The field stop method is generally more reliable when the manufacturer supplies an effective field stop diameter. Eyepiece distortion, barrel size, telescope openings, and accessories can limit the usable field. These calculations do not predict image quality or the best magnification for tonight.

Astrophotography calculator

See how your telescope and camera work together. Enter the active sensor dimensions from the camera specifications, not the camera body size. Example values are supplied; replace them with your own equipment.

Use 1 without an accessory, 0.8 for a 0.8× reducer, or 2 for a 2× Barlow. Actual factors can vary with spacing.

Pixel size is in micrometers (µm), not millimeters. This calculator assumes square pixels.

Use 1 for unbinned pixels, 2 for 2×2, or 3 for 3×3. Binning changes the angular size of an output pixel; it does not change the full sensor field of view. A cropped capture uses smaller active sensor dimensions.

Enter a seeing range for your sky, or the measured full width at half maximum (FWHM) of unsaturated stars in arcseconds. The starting 2–4 arcsecond range is an example, not a measurement of your location. For one measured value, enter the same number in both fields; leave both blank if unknown. We compare your pixel scale at the selected binning with a deep-sky reference band from the lower FWHM ÷ 3 to the upper FWHM ÷ 2. A setup within this band may still be under- or oversampled at one end of the seeing range. Optics, focus, tracking, and processing affect recorded detail too. This is not a universal target for planetary imaging. Read about this seeing-range method at astronomy.tools.

Enter your specifications and select Calculate imaging setup.

Camera field is calculated as 2 × arctan(sensor dimension ÷ twice the effective focal length). Pixel scale is approximately 206.265 × pixel size in µm ÷ effective focal length in mm. These are geometric estimates; distortion, vignetting, and the usable image circle may reduce the useful field. Pixel scale does not by itself predict resolved detail, tracking performance, or an ideal exposure.

Further reading: Starizona on pixel scale and field of view and astronomy.tools camera formulas.

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