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Determine power of a lens given the focal length. Lenses are found in a huge array of optical instruments, ranging from a simple magnifying glass to the eye to a camera’s zoom lens. In this section, we will use the law of refraction to explore the properties of lenses and how they form images.
The distance from the center of the lens to its focal point is defined as the focal length f of the lens. shows how a converging lens, such as that in a magnifying glass, can concentrate (converge) the nearly parallel light rays from the sun towards a small spot.
Each mirror has a radius of curvature r (which is infinite for the plane mirror) and a focal length f = 1 2r. By convention, distances are measured, along the central axis, as positive from the mirror in the direction of the object and negative away from the object.
More powerful lenses have shorter focal lengths and are much thicker (Figures 19.4 and 19.5). Lens makers use the unit of the dioptre (D) to define the optical power of a lens.
The thin lens equation relates the focal length of a spherical thin lens to the object position and the image position. The inverse of the focal length of a spherical lens is equal to the sum of the inverses of the image position and the object position.
the Gaussian lens formula relates focal length f, object distance s o, and image distance s i • these settings, and sensor size, determine field of view • 1:1 imaging means s o = s i and both are 2× focal length • s o = f is the minimum possible object distance for a lens 31 Questions?
When you have a sharp image, you measure the distance between the lens and the image (paper). This distance is the focal length of the lens. When the paper is held at a distance from the lens equal to the lens’s focal length, an image of the window forms on the paper.
