Dr. Lee is using an electron microscope and Dr. Murphy is using a light microscope.
An electron microscope has higher magnification and higher resolution than light microscopes. That's why the person who is using it , Dr. Lee, can see smaller structures(endoplasmic reticulum, the ribosomes, and the mitochondria) with same type of cell under the microscope.
This is achived by using beams of electrons instead of rays of visible light, like light microscopes do, to form highly magnified and high-resolution images of tiny areas of the cell.