There are three objective lenses attached to the rotating nose piece on this microscope.
Each lens has a different level of magnification. On this microscope the lenses are 4x, 10x and 40x.
When an object is viewed under the 4x lens, the total magnification is actually 40x.
The ocular lens (10x) is multiplied by the objective lens (4x) to give the total magnification (40x).
When observing an object under the microscope,
you should always begin by looking at the object under the lowest power (4x).
Once you have located and focused on the object using the coarse focus at 4x you may then increase the magnification to 10x.
Once you have refocused on the object using the coarse focus you may then use the fine focus.
The last lens you may use is the 40x lens, which requires the use of the fine focus.
Choosing an objective lens is the fourth step in using a microscope.