Please explain in detail the differences and characteristics of flat pentaprism.

SLR framing is based on the principle of pinhole imaging, so the phase inversion is obtained on the photoreceptor. In order to facilitate the photographer's observation, it is necessary to reverse the phase into a positive image through a pentaprism. For advanced machines, because the price is relatively high, manufacturers are willing to spend money to put a pentaprism cut from solid glass. For low-end machines, in order to save costs and flip the image at the same time, manufacturers use the principle of light refraction in pentaprism to install mirrors on several reflection points, which is the pentamirror. The pentaprism made in this way is actually empty inside, and the brightness is not as high as that of the pentaprism. The pentaprism made of high-quality optical glass has excellent optical performance, high reflectivity, minimal optical loss in the optical path and bright and clear field of view. But the high-quality pentaprism is expensive and heavy, which increases the cost and weight of the whole camera. In a pentaprism, only two reflecting surfaces actually participate in light turning. Therefore, some manufacturers widely use an optical device called pentaprism (or pentaprism) in low-end digital SLR cameras to simulate the optical path of pentaprism, rather than the function of pentaprism, that is, pentaprism. The pentaprism is solid glass, and there is a cavity in the middle of the pentaprism.