One formula · your inputs
Astronomy image scale calculator
Image scale connects physical pixel size with angular sampling at the entered effective focal length.
The 206.265 coefficient converts micrometres per millimetre into arcseconds per pixel in the small-angle model.
Formula
How it is calculated
scale (arcsec/pixel) ≈ 206.265 × pixel size (µm) ÷ focal length (mm)- Use the camera’s physical pixel pitch.
- Enter the effective focal length after reducers or extenders.
- Multiply per-pixel scale by pixel counts for an approximate field.
What the result represents
The small-angle conversion from radians to arcseconds with unit conversion from micrometres to millimetres.
The page keeps every decision-bearing quantity visible as an input. It does not look up a product catalogue, current market value or hidden recommended preset.
Limits of the model
The result is an idealised optical or geometric estimate from user-entered values. It does not model seeing, optical quality, central obstruction, transmission, distortion, focus error, tracking or sensor calibration.
Use the number to compare transparent scenarios. Verify critical observations, equipment combinations and coordinates independently.
Questions about this calculation
Does this image-scale calculator choose equipment for me?
No. It evaluates only the displayed formula with the numbers you enter and does not make a purchase, compatibility or safety decision.
Why can the observed result differ?
Real optics and observing conditions add obstructions, transmission losses, aberrations, seeing, focus and measurement uncertainty that are outside the arithmetic model.
Can I use the result for navigation or safety-critical work?
No. SkyClock tools are transparent planning estimates, not certified navigation, engineering or safety instruments.
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