Focal length
- Afrikaans
- العربية
- Asturianu
- বাংলা
- Беларуская
- Български
- Boarisch
- Català
- Čeština
- Dansk
- Deutsch
- Eesti
- Ελληνικά
- English
- Español
- Esperanto
- Euskara
- فارسی
- Français
- 한국어
- हिन्दी
- Hrvatski
- Bahasa Indonesia
- Interlingua
- Italiano
- Kreyòl ayisyen
- Lëtzebuergesch
- Lietuvių
- Magyar
- മലയാളം
- Bahasa Melayu
- Nederlands
- 日本語
- Norsk bokmål
- Norsk nynorsk
- Occitan
- Oʻzbekcha / ўзбекча
- Polski
- Português
- Română
- Русский
- Slovenčina
- Slovenščina
- Српски / srpski
- Srpskohrvatski / српскохрватски
- Suomi
- Svenska
- தமிழ்
- ไทย
- Türkçe
- Українська
- اردو
- Tiếng Việt
- 粵語
- 中文
Appearance
From Simple English Wikipedia, the free encyclopedia
![]() | This article needs more sources for reliability. Please help improve this article by adding reliable sources. Unsourced material may be challenged or removed. Find sources: "Focal length" – news · newspapers · books · scholar · JSTOR (Learn how and when to remove this message) |
The focal length tells how strongly a lens, a curved mirror or another optical device brings light together or spreads it out. If rays of light go straight into a lens and the focal length is positive, the focal length is the distance to the point behind the lens where the rays will be brought to a focus. If the focal length of the lens is negative, the focal length is the distance at which the light has spread to twice its original size. Light from a large distance produces an image at F (focal point). The distance from the centre of the lens to F is the focal length.