What is sharpness detection?

Brightness sharpness, also known as freshness sharpness and sharpness, is the ability of a photographic lens to vividly reproduce the low contrast shadow details, weak brightness contrast and subtle color changes in the middle and deciduous layers of a scene. With high-definition lens, the image has clear outline, sharp edge, normal contrast, rich layers, delicate texture, clear tone, strong texture, soft color transition and true and natural color restoration. Obviously, these characteristics are indispensable qualities of high-quality photographic lenses. However, it is difficult to simply express the brightness and sharpness of the photographic lens with data, and it is also difficult to test it with ordinary instruments. People usually make qualitative comments only on subjective feelings. The comprehensive performance of resolution and clarity is called clarity. Obviously, resolution and sharpness are two important factors to comprehensively evaluate the imaging quality of a photographic lens. A lens with high resolution and low Ming Rui produces an image with dim outline, sharp edges, gloomy contrast and dull tone, which gives people a vague visual experience. Some mid-range lenses in Japan, many lenses in Russia, and most domestic lenses are like this. Some lenses in Germany, although the resolution is not high, but the sharpness is quite high, are still an excellent lens. Of course, if the definition and resolution are high, it is indeed an ideal photographic lens. However, this kind of lens is very rare. Only the German famous brand fixed-focus photographic lenses and a few Japanese famous brand photographic lenses that have been strictly tested and repeatedly selected can have these two qualities at the same time. The optical performance of the lens generally increases with the decrease of the aperture. When the aperture is large, most of the surface of the lens glass should be used, so the inevitable processing errors in the manufacturing process will cause slight image blur. Narrowing the aperture means using only the middle part of the lens glass, so the imaging is more accurate and the resolution can be improved. As the rising curve in the figure, the starting point is 40, which is called "optical" or theoretical brightness. However, in fact, things are not so simple. A phenomenon called diffraction will make things worse.