what is the lens under the condenser?

[92111]

new baught a two hand microcsope ,lomo biolam
what is the lens under the condenser? kohler illumination?
picture from internet:

[daruosha]

I guess is't a field extender for low magnification like 1x or 2X objectives.

[apochronaut]

Usually with an average field condenser, that aux. lens is required for anything from about 5X down. Once you get to 2.5X or so, even that isn't enough. They usually need some way of removing the top condenser lens.

[92111]

thanks ,if i don't reply you, that must because my English is poor