magnifying power of telescope

Question

why does telescope with lower magnifying power provide brighter image?

Answer 1

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The area occupied by a small size image produced by a low magnifying power is smaller than the area occupied by a large size image produced by a high magnifying power. Assume the light enetering into the telescope from a distance object is the same, then it is apparent that the light spreads out over a smaller area of the small size image, but over a larger area of a large size image. Hence, the amount of light seen per unit area on the small size image is larger than the amount of light seen on unit are of the large image. The small size image therefore looks brighter.