think to see cells, you need at least 700-1000 times
magnification?
optical microscopes can only go up to 1000 times max...but have to
trade between depth of view and field of view...not so good.
for >1000 times up to 500,000 times max...you need an electron
microscope, but samples may need to be conductive, else cannot see
anything...higher mag ones you can use field-emission or high-mag
electron microscopes..
for up to 1 million times and over, use TEM. (can see atoms some
more)! 
