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I am confused on how light rays behaved in this figure, specifically when it passed through the diverging lens. Why would the light rays converge when it passed through the diverging lens, when it should have diverged? enter image description here Shouldn't the light rays have diverged instead? This was from a textbook and how zoom lenses work.

This was how I pictured the light rays would be. The blue lines would be the normal lines. Is it not correct? I mean light rays should have bent away from the normal lines since the light ray was entering through a material with lower index of refraction. enter image description here

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  • $\begingroup$ Note that if the rays between the lenses were extended they would meet closer less than 24 cm from the diverging lens. The diverging lens does diverge the rays and they meet at 24 cm from the diverging lens. $\endgroup$
    – Farcher
    Commented May 14, 2017 at 21:37
  • $\begingroup$ So even if the light rays were from a diverging lens, they would still diverge at some point? $\endgroup$
    – Czar Luc
    Commented May 14, 2017 at 21:42
  • $\begingroup$ In your first diagram after passing though the diverging lens the rays are converging less i.e. Diverging more. In you second diagram the diverging lens has a much shorter focal length and so refract (bend) the rays more. $\endgroup$
    – Farcher
    Commented May 14, 2017 at 22:04
  • $\begingroup$ So the effect of putting the diverging lens next to a converging lens just lowers the effect of converge? $\endgroup$
    – Czar Luc
    Commented May 14, 2017 at 22:06
  • $\begingroup$ That is correct and in the second diagram so much so that the rays that emerge are actually diverging. $\endgroup$
    – Farcher
    Commented May 14, 2017 at 22:08

1 Answer 1

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Considering a real object, a diverging lens will make a virtual image, that is rays will diverge. However, this is the opposite with a virtual object: it will make a real image. In other words, the object and the image of a diverging lens are on the same side of the lens. In your case, the rays entering the diverging lens would focus after the diverging lens, so their image will be after the lens.

However, this doesn't mean that rays won't diverge. In fact, you can see in the figure that the refracted rays are less inclined than the incident ones, they are diverting from the axe. In other word, the beam is diverging.

Finally, your figure is wrong: as a said on the second paragraph, a beam doesn't have to focus on the left of the lens after going through a diverging lens, eg. when it comes from a virtual object, it will focus on the right of the lens.

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