A wildlife photographer uses a camera with a convex lens to capture an image of a rare bird perched on a branch. The bird is positioned further from the lens than twice its focal length, but the photographer wants the resulting image to be the same size as the real bird. Which lens adjustment would most effectively allow the photographer to achieve this goal, based on ray diagram principles?
Move the lens so the bird is exactly at twice the focal length from the lens
For a convex lens, the size of the real image depends on where the object stands relative to the focal length F and twice the focal length 2F. Ray diagrams give three useful cases for a real object.
When the object is beyond 2F, the image is formed between F and 2F on the other side and is real, inverted and smaller than the object. This is the bird's present position, so the image is diminished.
When the object is exactly at 2F, the image is formed at 2F on the other side and is real, inverted and of the same size as the object. So the lens must be moved so that the bird is exactly at twice the focal length.
Moving the lens closer so that the bird is between F and 2F gives an enlarged image beyond 2F, and moving it farther keeps the bird beyond 2F, giving an even smaller image. Flipping a convex lens does not change its focal length, so the image stays diminished.
Hence, Move the lens so the bird is exactly at twice the focal length from the lens.
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Important Questions from Optics
Who was the first one to use a glass prism to obtain the spectrum of sunlight?
Twinkling of stars is due to:
In which a convex mirror is used?
A. Rear View mirrors in vehicles
B. Glass windows
C. Makeup Mirror
D. Kaleidoscope
An object is placed 10 cm in front of a lens. The image formed is real, inverted and of same size as the object. What is the focal length and nature of the lens?
The power of a lens is -2.5 D. The type of lens and its focal length are respectively:
