The lens is an optical element with a spherical surface made of transparent material. The lens is composed of several lenses, There are plastic lenses and glass lenses Glass lens is more expensive than plastic lens. Generally, the lens structures used for cameras are: 1p, 2p, 1g1p, 1g2p, 2g2p, 4G, etc. The more lenses, the higher the cost. Therefore, a good quality camera should use glass lens, which has better imaging effect than plastic lens, and plays an important role in astronomy, military, transportation, medicine, art and other fields.
concept
Lens can be widely used in security, vehicle, digital camera, laser, optical instrument and other fields. With the continuous development of the market, lens technology is more and more widely used. (lens) a lens is made according to the refraction law of light. A lens is an optical element made of transparent substances (such as glass, crystal, etc.). A lens is a refractor, and its refracting surface is a transparent body with two spherical surfaces (part of the spherical surface), or a spherical surface (part of the spherical surface) and a flat surface. Its image has both real and virtual images.
Convex Lens: thick in the middle and thin at the edge, including biconvex, flat convex and concave convex;
Concave Lens: thin in the middle and thick at the edge, including double concave, flat concave and convex concave.
Little formula
1. Lens
The lens can transmit light; Middle thick, convex lens; Thin, concave lens in the middle.
Convergent convex lens, divergent concave lens.
The flat light converges to a point, represented by focus F.
The distance from the focal point to the optical center of the mirror is called the focal length of the mirror (expressed by F).
2. Lens in life
The object is far like a close camera, the real image is reduced and inverted.
Object near image far projector, enlarge the real image and stand upside down.
A magnifying glass on the same side of the object image magnifies a virtual image upright.
The real image is inverted, the virtual image is positive, and the virtual image on the opposite side of the real image is the same.
3. Convex lens imaging law and Application
The object is imaged between one and two times (focal length) beyond twice the focal length.
The real image is inverted and reduced. This example is used in the camera.
Things move closer, images move farther, and images get bigger.
The object is imaged outside the double focal length between one and two times the distance.
The real image is inverted and enlarged. This example is used in the projector.
The object is in the focus, and the moving light screen does not see the image.
Look at the object through the lens and enlarge a virtual image upright.
The object is on the same side as the image. This example is used for a magnifying glass.
The near image and the far image of the object become larger, and the far image and the near image of the object become smaller.
Twice the focal length is divided into size, and twice the focal length is divided into virtual and real.
As the object distance decreases, the real image becomes larger and farther, and the virtual image becomes smaller and closer.
Explanation:
When the object is outside the focal length of the convex lens, the convex lens becomes a real image. When the object is outside the double focal length of the convex lens (U > 2f), the convex lens becomes a reduced real image.
When 2F > U > F, it becomes an enlarged real image. The virtual image and real image without reduction are inverted, and there is no inverted virtual image.
expand
The knowledge points about lens and its application expansion in the junior middle school applied physics knowledge competition mainly include:
1. Three principles (three special rays) for lens imaging mapping: ① the light parallel to the main optical axis passes through the main focus after being refracted by the lens; ② the direction of the light passing through the optical center remains unchanged after being refracted by the lens; ③ the light passing through the main focus is refracted by the lens and then parallel to the main optical axis.
2. Convex lens imaging formula: 1 / u (object distance) + 1 / V (image distance) = 1 / F (lens focal length). Understanding of convex lens imaging law:
a) One conclusion: reality is different, deficiency is the same. That is, the real image is always upside down on the opposite side, which can not only be seen, but also be carried on with a light screen; The virtual image is always standing on the same side, which can be seen, but can not be carried on with a light screen.
b) Two dividing points: focus and 2x focal length. Focus is the dividing point between real image and virtual image. When the object is within the focus of the convex lens, it becomes a virtual image; When the object is outside the focus of the convex lens, it becomes a real image. It can be abbreviated as: the focus is divided into internal and external virtual reality, internal virtual and external reality. The point at twice the focal length is the dividing point between the enlarged image and the reduced image. When the object is located between 2 times the focal length and the focus of the convex lens, it becomes an enlarged real image; When the object is located outside the focal length of the convex lens, it becomes a reduced real image. It can be abbreviated as: 2 times the focal length, the point is divided inside and outside, the inside is large and the outside is small.
Three changes: ① changes in image size and image distance: when the object moves closer to the focus, the image becomes larger and the image distance becomes larger. ② Change of image object moving speed: the object is located outside the point at twice the focal length (U > 2f), the object distance is greater than the image distance, the real image is reduced upside down, and the object moving speed is greater than the image moving speed; the object is located between the point and the focus at twice the focal length (f < U < 2f), when the object distance is less than the image distance, it becomes an inverted enlarged real image, and the moving speed of the object is less than the moving speed of the image. ③ distance change between objects and images: when the object is located at 2 times the focal length, the imaging is at 2 times the focal length on the other side, the object image distance is the smallest, which is equal to 4 times the focal length. When the object is located outside the 2 times the focal length, the imaging is between the focal point on the other side and the 2 times the focal length, and the object moves towards 2 times the focal length When the point moves, the distance between objects and images becomes smaller; When the object moves away from the point at twice the focal length, the distance between objects and images becomes larger. When the object is located within the 2x focal length (between the focus and the point at the 2x focal length), the imaging is outside the 2x focal length on the other side, the object moves to the point at the 2x focal length, and the distance between objects and images becomes smaller; when the object moves to the focus, the distance between objects and images becomes larger.
The object lens is a final electromagnetic lens that focuses the electron beam on the substrate [1].
