Your numbers
Aperture (f-number)
For example 2.8.
Focal length (mm)
The real focal length on the lens, not the 35 mm equivalent.
Pixel pitch (µm)
Or fill in the sensor width and pixels below.
Declination of the target (°)
Optional. Empty means 0, the celestial equator.
Sensor width (mm)
Pixels across the sensor width
Crop factor for the 500 rule
Optional, 1 for full frame. The 500 rule uses the equivalent focal length.
Calculate
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Result
Fill in the fields and press Calculate.