1, occlusion

Usually, improper shading bucket will lead to little or no light entering some pictures.

2. The frames of the lens and the SLR don't match.

Usually, zoom lenses in some sub-factories will have this phenomenon, some focal segments can be imaged normally, while others have black edges.

Method of purchasing lenses

Most friends don't change their lenses often. The lenses of digital cameras are generally divided into optical zoom lenses and fixed focus lenses. For consumer digital cameras, the imaging quality of optical zoom lens is much better than that of fixed-focus lens, which is contrary to SLR lens, because in consumer digital cameras, the workmanship and material of fixed-focus lens are generally not as good as that of optical zoom lens.