Bellow unit extends the distance between the lens and the film plane / CCD on the cameras, increasing the magnification of the subject on that film plane / CCD. It is a similar concept to moving a slide projector further away from the white screen to increase the size of the projection It is far more convenient than keep staging multiple extension tubes because it requires less fiddling and changing. Next, the amount of extension for bellow is far greater than extension ring set which resulted in higher magnification ratio at will.
Bellows are best used with a tripod for stability and ease of use - allowing you to smoothly and constantly adjust the distance between your camera and the object you want to photograph. There is a UNC 1/4 screw at the bottom. This product is a step up from the macro extension ring and is invaluable for anyone wishing to take extremely close-up pictures, particularly those of plants and flowers. The rail can be extended up to 150mm. Magnify ratio is 0.74-2.86:1 while using an f50 lens, and is 1.32-5.1:1 that of f28 lens.