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Focal Ratio

Definition: The focal ratio, also known as the f-number or f-stop, is a numerical representation of the speed of a camera lens or a telescope. It determines the amount of light admitted by the lens and the depth of field in the resulting image.

Sense 1: In photography, the focal ratio represents the aperture size of a camera lens. It is calculated by dividing the focal length of the lens by the diameter of the aperture. A smaller focal ratio indicates a larger aperture, allowing more light to enter the camera, ideal for low-light conditions.

Sample Sentence 1 (Photography): I shot a stunning landscape photo at night by using a lens with a wide focal ratio of f/1.4, which allowed enough light to capture the starry sky.

Sense 2: In astronomy, the focal ratio represents the relative amount of light-gathering capability and the angular field of view of a telescope. It is calculated by dividing the focal length by the diameter of the objective lens or primary mirror.

Sample Sentence 2 (Astronomy): The telescope with a high focal ratio of f/12 is excellent for observing planets, as it provides a narrower field of view and offers high magnification.

Local Usage: In the local astronomy club, the astrophotographers often discuss the best focal ratios for capturing deep space objects.

Related Products: To explore and select suitable camera lenses or telescopes, you can check out the following products:

• Camera Lenses on Amazon
• Telescopes on Amazon