If you have an FD91 with 14x zoom, the teleconverter will give you 14x2x, or 28x. Other Mavicas have between 3x and 10x. With a 2x teleconverter, you'll be able to get 6x and 20x respectively. To practically go beyond 28x with a Mavica, you'll need to attach a more unconventional device to your camera. Telescopes will give you the most powerful magnification for distant objects.
Telescopes range in power and size.
I know little about them, so I won't get into a discussion beyond that. If you're interested in photo microscopy, then a microscope would be required. Again, I don't have a microscope, and can only rely on my high school education to talk about them. O.K., perhaps you have a pair of binoculars in a drawer somewhere. That's something I know about.