The dentist endoscope is a dentist is the use of teeth in the plane mirror into an equal image, by observing the image to observe the teeth, and make a diagnosis. The principle is the reflection of light.
(2) convex lens imaging law:
U>2f, into an inverted, shrunken solid image, made of cameras.
2f>U>f, inverted, magnified solid image, made of slide projector.
U < f, into an upright, magnified virtual image, made of magnifying glass.
The answer is: (1) the first category: periscope, mirror, dental endoscopy, using the principle of reflection of light made.
(2) the second category: cameras, slide projectors, magnifying glasses, using the principle of refraction of light made.