What are these things called?
Which is the high dry?
Which is the oil immersion?
Which is the low?

What are these called?
The one on the right seems to have a ring around it which the other one doesn't have.  
What is that used for?

What is this part of the microscope called?
 

What are the knobs on the right called?
What about the knobs which are hanging from the top of the picture?