Measurement of lens focal length

Measurement of lens focal length, sun light focusing method (rough measurement focal length method): Place the convex lens facing sunlight and place a piece of paper on the other side, changing the distance between the lens and the paper until the light spot on the paper becomes the smallest and brightest. This spot is the focus of the convex Led Lighting Lens. Measure the distance between the minimum spot and the convex lens using a ruler, which is the focal length.

The principle of convex led lens imaging: When an object is placed outside the focus, an inverted real image is formed on the other side of the convex LED Lens, which can be reduced, equal in size, or enlarged. The smaller the object distance, the larger the image distance, and the larger the actual image. The object is placed in focus, and the convex lens forms an upright magnified virtual image on the same side. The larger the object distance, the larger the image distance, and the larger the virtual image. Will not image in focus. When the focal length reaches twice, an inverted real image of equal size will be formed.

In optics, the image formed by the aggregation of actual light is called a real image, which can be carried by a light screen; On the contrary, it is called a virtual image and can only be felt by the eyes. Experienced physics teachers often mention the method of distinguishing between real and virtual images: inverted real image and upright virtual image. Compared to the original object, the so-called upright and inverted are of course relative.

The three types of virtual images made of flat mirrors, convex mirrors, and concave lenses are all upright; The real images made of concave mirrors, convex lenses, and small hole imaging are all inverted without exception. Of course, concave mirrors and convex lenses can also become virtual images, and both virtual images are also in an upright state.