You can't adjust your F-Stop with dark lenses. F-Stop is not a measure of light coming in, it's a measure of the focal length to the aperture. Light conditions prior to hitting the aperture (Either by flashes, sunlight, or dark lens) are entirely separate from the concept of F-Stop.

For a given focal length on a subject in focus at a reasonable distance (not at infinity), increasing the F-Stop will always increase the DOF.