दूरबीन फ़ोकल अनुपात कैलकुलेटर — सूत्र
## 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
**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
हल किया गया उदाहरण
1200 mm focal length, 200 mm aperture.
- f/# = 1200 / 200 = f/6
- This is a moderately fast scope, good for both visual and imaging.