I used to use extension tubes on my 35mm when I was into insect photography. Either with a 50mm or 135mm lens. You can’t easly focus the camera, just move backwards and forwards until it is clear.
I found the best solution to focus, depth of field and ease of use, was to mount two small flash guns one on either side of the lens. For any given magnification or selection of rings you used the same aperture settings, as you got closer the less light gets to the film, but the brighter the effective flash is, and it all evens out. No worries about camera shake either because it’s the flash duration and not the shutter speed that controls the exosure, som you won’t need a tripod.