If reflection is used instead of refraction and if the curved mirror is highly reflective and cast the image of the galaxy in a obscure chember on a relatively distant screen how much the image can be larger than the image before the enlargement on the screen? enter image description here

  • $\begingroup$ Depends on how faint you can detect light. The total amount of light will be quite small to start, and you then spread it out. Also, I'm not able to design in my head the shape required of your mirror. Have you got that handy? $\endgroup$
    – Dan
    Jan 20 at 22:07
  • $\begingroup$ @Dan Let say it is a parabolic convex mirror of small dimensions to provide greater curvature. In case of sources somebody can use sirius if galaxies are too faint.... $\endgroup$ Jan 20 at 22:32

1 Answer 1


A mirror wit this convex shape can not make a picture, so your sketch is wrong. you have to use a concave mirror. The picture will be in the focal distance. and you use a magnifying lens to see it. You can look it up under "reflecting telescope"

  • $\begingroup$ I think paralel rays from the source should spread out when reflected from the convex mirror and form a large image on the distant screen... $\endgroup$ Jan 20 at 23:54
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    $\begingroup$ Yes, they spread out, that's why there is no picture of the galaxy, just light. To have a picture, rays coming from one point of an object have to meet at one point, or almost one point. $\endgroup$
    – trula
    Jan 22 at 22:07

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