How to understand the definition of maximum magnification of SLR lenses? What does it have to do with focal length?

Magnification ratios such as 1:1, 1:4, etc. refer to the ratio of the size of the actual object to the size on the film. 1:1 means that the actual object is the same size as the image on the film. 1:4 is 1/4 of the size of the actual object on the film.

The magnification you use mainly depends on the size of the object you are photographing. For example, if the plum blossom you mentioned is 1:1, it will still fit on the 135 film! So if you want to take micro-focus effects, you should use a micro-focus head! I can only say that I can get a good depth of field effect when shooting for a small amount of time, but there is no mention of micro-focus. There are also telephoto lenses with micro focus.

In addition, if you want to shoot micro focus with a small digital camera or SLR camera, you can also use a close-up lens (poor dispersion control), close-up lens (large light loss), reverse standard (positive standard), leather cavity, etc. method! However, it is still very good to use a good close-up lens (set) for micro-focus photography.