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Old Sep 8th 2009, 02:35 AM   #1
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Join Date: Apr 2009
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Cool Magnifying Lens question

I just read something in my physics book that says:

"If the eye is relaxed (for least eye strain), the image will be at infinity and the object will be precisely at the focal point."

I don't really understand this. Are you manually moving the magnifying glass? The way they right it, I'm imaging the object just within the focal point of the converging lens, but then when you let your eyes rest, it magically moves to the focal point?

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Old Sep 10th 2009, 11:52 PM   #2
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Join Date: Feb 2009
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It would help if you quote the enitre context.

What may be meant is this.

When we use a magnifying glass (convergent lens), we try to get the object into focus.

Rays from an object at infinity are treated as parallel. That is why if you try to get an image of the sun on a piece of paper, it forms at the focus.
Conversely, the rays from an object at the focus emerge parallel from the convex lens. If we extend these rays backward, they appear to come from infinity.
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