How to increase the optical magnification of a microscope?

[vtl-dch]

Hello!
I have a microscope with a magnification of 180.
When I reduce the distance between the lens and the object of observation and increase the distance between the eyepiece and the lens, I get an optical magnification of the microscope 800. I can’t get any more, because the lens rests on the object.
Please tell me why the optical magnification is increasing?

I use Google translate. Sorry for the incorrect translation.

 

[swansont]

The magnification of a simple telescope/microscope is the ratio of the focal lengths of the objective lens and the eyepiece. If you have a more complicated system, you are changing the effective focal length when you turn the knob. 
You can change the magnification by changing the eyepiece