My recommendation past 5x would be - YES - a microscope objective! Olympus S-Planar objectives are quite nice. As are the Leitz (Wild-Heerbrugg) and Nikon designs. Screw the shutter though. Why would you need it? Any ambient light shots could easily be dealt with by a lenscap - (you're probably looking at 10 plus seconds even in sunlight) or if you're using a strobe - well - I don't need to tell you.