Camera image scale in astrophotography
Image scale combines pixel size and effective focal length to state how many arcseconds fall on one pixel.
Enter the complete optical train
Use the camera’s real pixel size and effective focal length after a reducer, Barlow or corrector. Native focal length without the factor produces the wrong result.
With hardware or software binning, effective pixel size changes according to the grouping used.
Interpret it with conditions
A smaller arcseconds-per-pixel value means finer sampling, not guaranteed extra information. Seeing, tracking, focus and diffraction may be stronger limits.
Very fine scale raises mount requirements and may reduce signal-to-noise per pixel.
Compare scale and camera field
A system can have attractive sampling but too little field for the target. Calculate both before buying adapters or correctors.
For mosaics plan overlap and sensor orientation separately; TelescopeTo does not create an automatic sky plan.
Verify in practice
Take a test series and inspect star shape at centre and corners. Record effective focal length, binning and tracking settings.
Compare changes on the same target in similar conditions rather than unrelated nights.
Common mistakes
- Ignoring a reducer or Barlow factor.
- Assuming the smallest scale is automatically best.
- Ignoring sensor field of view.
- Comparing sessions with completely different seeing.
What to record in TelescopeTo
- Camera, pixel size, binning and effective focal length.
- Calculated scale and sensor field.
- Star-test result and tracking conditions.
Guide limits
The calculator describes geometry. It does not predict real sharpness, corrector quality, tilt, tracking or camera noise.