Calculateur de Rapport Focal de Télescope — Formule

Focal Ratio (f-Number)

f/# = Focal Length / Aperture

Lower f-numbers ("faster" scopes) collect light over a wider cone and are better for astrophotography of faint objects. Higher f-numbers ("slower") give longer focal lengths for planetary detail.

  • f/4 to f/5: fast, wide-field
  • f/8 to f/10: moderate, good all-round
  • f/12+: slow, high magnification

    • Exemple Résolu

    1200 mm focal length, 200 mm aperture.

    1. f/# = 1200 / 200 = f/6
    2. This is a moderately fast scope, good for both visual and imaging.