Why am I transparent when I shoot people with multiple exposures?

When exposed for many times, the black part, that is, the unexposed part, will produce an image again when exposed for the second time! Is that clear?

Generally speaking, it can be said that the larger the aperture, the smaller the depth of field, and the closer to the subject, the smaller the depth of field. This depth of field is not necessarily the background, but the distance you focus.