(1)The focal length can be changed uniformly as well as continuously.  With the increasing improvement of processing and assembling technology, the application of the zoom structure is becoming more and more common, and its function is becoming more and more convenient. In the continuous zoom system, the focal length can be uniformly changed between the maximum and the minimum focal length, and can also take any focal length value within the range. (2)The image plane remains stable during continuous zooming.  The so-called image plane remains stable, usually in two aspects: first, the stability of the position of the phase plane during zooming; second, during zooming, the size of the image formed by the system remains unchanged. (3)The image quality meets the requirements.  The requirement of the continuous zoom system on the imaging quality is not only good imaging quality for some unique focal length positions, but also requires the imaging quality to be as consistent as possible in the entire zoom range. Thus, it requires that the motion of the zoom group and the compensation group be well connected. The motion curve should be smooth, and unnecessary inflection points should be avoided as much as possible.