What is the best aperture value?

The lens can produce the sharpest image aperture value on the CCD (or film) plane with proper focus. For most quality lenses, the best aperture value is to reduce its maximum aperture by one to two degrees. For example, when shooting with a lens with a maximum aperture of f/2.8, the resulting image quality should be optimized for apertures of f/4.0 or f/5.6.

Theoretically, the larger the aperture, the better the image quality will be, but the aberration will increase sharply with the increase of the aperture, which will degrade the image quality. In addition, if the aperture is too small, diffraction will occur (in digital photography, a small aperture will also increase the exposure time and make the image appear noisy), which will degrade image quality. Therefore, the best aperture value is to avoid the balance between the above two phenomena, that is, the maximum aperture value is one to two levels lower.