There are several companies that are known for manufacturing microscopes, and it is difficult to determine which one is the largest. Some of the major players in the microscope industry include:

• Olympus: This Japanese company is a leading manufacturer of microscopes and other scientific instruments. They offer a wide range of microscopes for different applications, including biological, material science, and industrial microscopes. 

• Nikon: This Japanese company is a well-known manufacturer of optical instruments, including microscopes. They offer a wide range of microscopes for different applications, including biological, material science, and industrial microscopes.

• Leica Microsystems: This company is based in Germany and is known for producing high-quality microscopes for a variety of applications, including research, industrial, and educational settings.

• Zeiss: This German company is a leading manufacturer of microscopes and other scientific instruments. They offer a wide range of microscopes for different applications, including biological, material science, and industrial microscopes.

It's worth noting that there are many other companies that manufacture microscopes, and the market is constantly evolving. It's also worth considering that some companies may specialize in certain types of microscopes or have a strong presence in certain regions or industries.