The zoom ratio is the ratio between the maximum focal length and the minimum focal length in an optical device such as a lens or microscope. This parameter is one of the most important indicators of the performance of a lens, and directly determines the angle of view and the size of the image that can be captured by the lens.

In a zoom lens, the zoom ratio is particularly important because it determines the lens' magnification ability and range of application at different focal lengths. For example, a lens with a zoom ratio of 6.5:1 means that its maximum focal length is 6.5 times its minimum focal length. This design allows the lens to zoom over a wide range of focal lengths, thus adapting to different shooting scenes and subject distances.

For the exact value of the zoom ratio, it may vary from one lens series and product to another. The 6.5X series of zoom lenses, for example, has a 6.5:1 zoom ratio, which usually means that the lens has a wider range of focal lengths to choose from, and is able to cover different shooting needs from wide-angle to telephoto.

The zoom ratio is a parameter to focus on during the selection process. A larger zoom ratio usually means a wider range of focal lengths to choose from, but at the same time, it may also bring some challenges, such as the control of image quality and the complexity of lens design. Therefore, when choosing a zoom lens, the relationship between the zoom ratio and other parameters needs to be balanced according to specific application scenarios and needs.

In addition to the zoom ratio, zoom lenses have other important parameters to consider, such as resolution, working distance, aberration, and so on. Together, these parameters determine the performance and scope of application of the lens. Therefore, in the selection process, these factors need to be considered comprehensively in order to choose the most suitable zoom lens for your needs.