Well, I actually did end up getting a diopter. Although I can auto focus from within 4" from the subject, the images captured at that distance all came out blurry for some reasons. I guess this is what is called narrow depth of field? But, at about 8" from the subject, I could get some OK shots. The macro is quite as "macro", but is doable for me. Here's a few samples.
No flash on the first shot and built in flash on the second shot. Still difficult to get a good shot as lighting is still a challenge since I am not using an off body flash. So, I can't capture any fish as they are always moving, and I can't speed up the shutter speed as the pic will under expose.
The diopter I got is a B+W 77mm +5.
BTW, these are Nick's famous shrimps.