How do cameras, magnifying glasses and projectors work?

convex lenses are made according to the refraction principle of light.

a convex lens is a lens with a thick central part. Convex lenses are divided into biconvex, plano-convex, concave-convex (or positive meniscus) and other forms. Thin convex lenses are also called condenser lenses because of their convergence, while thicker convex lenses have telescopic, divergent or convergent effects, which are related to the thickness of the lens.

parallel light (such as sunlight) is injected into the convex lens parallel to the axis (the line connecting the spherical centers of the two spherical surfaces of the convex lens is called the main optical axis of this lens), and the light is refracted twice on both sides of the lens and concentrated at a point on the axis, which is called the focal point of the convex lens (marked as F). The convex lens has a focal point on both sides of the mirror. If it is a thin lens, the distance between the two focal points and the center of the lens is approximately equal. The focal length of a convex lens refers to the distance from the focal point to the center of the lens, which is usually expressed by F. The smaller the spherical radius of convex lens, the shorter the focal length. Convex lenses can be used for magnifying glasses, glasses worn by presbyopia and hyperopia, cameras, film projectors, microscopes, telescopes and so on.

Experimental study on the imaging law of convex lens is as follows: when the object distance is less than one focal length, an upright and enlarged virtual image is obtained; When the focal length is between one and two times, the inverted and enlarged real image is obtained; Outside the double focal length, the inverted and reduced real image is obtained.

this experiment is to study and confirm this rule. In the experiment, there is the following table:

the position of the property image of the object distance U image

the vertical or inverted image enlarges or reduces the distance between the virtual image or the real image and the object on the same side and on the opposite side v

u> 2f Inverted reduction of the opposite side of the real image f <: v< 2f

u=2f, inverted image, etc., opposite side v = 2f

f <; u< 2f Inverted amplification of opposite side of real image v> 2f

u = f-(meaningless, not like)

u <; F is upright to enlarge the same side of the virtual image, and the same side of U and V < P > is a table designed to confirm that rule. Actually, lens imaging satisfies the lens imaging formula:

1/u (object distance) +1/v (image distance) =1/f (lens focal length)

The camera actually uses the imaging principle of convex lens. A convex lens, let the focal length be f (the convex lens can converge light, and the point where the light converges is called the focal point, and the distance from the focal point to the center of the convex lens is the focal length), and the object distance (the distance from the object to the center of the convex lens) be u, then, when u >; 2f, an opaque object is placed on the other side of the convex lens, which is called a light screen in physics, and an image identical to the real object can be obtained on the light screen, but this image is inverted and reduced.

A simple visual optical device used to observe the details of an object is a convergent lens with a focal length much smaller than the apparent distance of the eye. The size of the object imaged on the human retina is directly proportional to the angle (viewing angle) of the object to the eye. The bigger the viewing angle, the bigger the image, and the more you can distinguish the details of the object. Moving closer to the object can increase the viewing angle, but it is limited by the focusing ability of the eyes. Use a magnifying glass, make it close to the eyes, and put the object within its focus to form an upright virtual image. The function of a magnifying glass is to enlarge the viewing angle.

The object is not imaged in the focus, but the double focal length is the same.

The inverted image is smaller than the second focal length, and the slide is put outside the focus.

When the object is placed in the focus, the opposite side can see a big virtual image.

If the image can be displayed on the screen, it must be inverted as a real image.

1. u > f becomes a real image, and u < f becomes a virtual image. The focus is:

2. u > 2f is the reduced real image, and u < 2f is the enlarged real image. The double focal length point is the dividing point between the enlarged real image and the reduced virtual image.

3. When a real image is formed, when the object distance decreases, the image distance increases and the image becomes larger; When the object distance increases, the image distance becomes smaller and the image becomes smaller.

4. when a real image is formed, the image and the object are on different sides of the convex lens, and when a virtual image is formed, the image and the object are on the same side of the convex lens.

5. The real image is the convergence of actual light, which can be displayed on the screen, while the virtual image is the intersection of the reverse extension lines of refracted light, which is not displayed on the screen.