Kostenloser Telescope Focal Ratio Rechner
Berechnen Sie den focal ratio (f-number) of a telescope. Kostenloser optics Rechner.
Focal Ratio
6.0 f/
Focal Ratio vs Focal Length
Formel
## 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
Lösungsbeispiel
1200 mm focal length, 200 mm aperture.
- 01f/# = 1200 / 200 = f/6
- 02This is a moderately fast scope, good for both visual and imaging.
Häufig Gestellte Fragen
Why does focal ratio matter for photography?
Faster (lower f/#) means shorter exposure times for the same signal. An f/4 scope requires 1/4 the exposure of an f/8 for extended objects.
Does focal ratio affect visual brightness?
For point sources (stars), no - only aperture matters. For extended objects (nebulae), faster focal ratios give brighter images at the eyepiece.
What is a typical focal ratio?
Schmidt-Cassegrains are typically f/10. Newtonian reflectors range from f/4 to f/8. Refractors for astrophotography are often f/5 to f/7.