"Eyes and Glasses" Common Optical Instruments PPT Courseware 3

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"Eyes and Glasses" Common Optical Instruments PPT Courseware 3

1. The principle of seeing with the human eye: imaging through a convex lens similar to a camera

The cornea and lens work together as a convex lens.

The retina is equivalent to a light screen.

normal eyes

The lens, cornea and other tissues work together to act as a convex lens, through which the light rays emitted from the object converge on the retina to form an image of the object.

When looking into the distance: the ciliary body is relaxed, the lens is thin, and the focal length is longer. The light from distant objects just converges on the retina, and people can see distant objects clearly.

When looking closely: the ciliary body shrinks, the lens is thicker, and the focal length is shorter. The light from nearby objects converges on the retina, and people can see nearby objects clearly.

2. The principle of how the human eye can see distant and near objects clearly: the adjustment function of the lens

When the ciliary body relaxes, the lens becomes thinner, allowing light from a distance to converge on the retina, and the eyeball can see distant objects clearly.

When the ciliary body contracts, the lens thickens, allowing light from nearby areas to converge on the retina, allowing the eyeball to see nearby objects clearly.

3. Myopia and its correction

1. Cause:

The lens is too thick and its refractive power is too strong, causing the image to appear in front of the retina.

2. Correction:

Wear myopia glasses made of concave lenses.

Normal eyes, myopic eyes, farsighted eyes

The difference between the three:

What does the normal eye see?

What will myopia and hyperopia look like after correction?

(4) Discussion: The power of glasses

1. What is lens power?

The reciprocal of focal length, Φ=1/f, unit: m-1

2. What is the power of glasses?

The power of the lens is the value of the lens power multiplied by 100, D=100Φ, unit: degree

3. What do the positive and negative powers of glasses mean?

The positive and negative powers of glasses represent convex lenses and concave lenses respectively.

Class exercises:

1. Under normal circumstances, the image received on the retina looks like _____; after adding corrective glasses, the image received on the retina looks like _____. (Fill in "real" or "virtual")

2. Myopia can only see nearby objects. The possible reason is ( )

A. The lens is too thick; B. The lens is too thin;

C. The image is behind the retina; D. The eyeball is too long.

3. The possible reason why hyperopia cannot see nearby objects clearly is ( )

A. The eyeball is too short; B. The lens is too thin;

C. The image is formed in front of the retina; D. The image is formed in front of the retina.

summary:

1. Principle of seeing with human eyes:

2. The principle of seeing distant and near objects clearly with the human eye:

3. Myopia and its correction

4. Hyperopia and its correction

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Update Time: 2024-10-02

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