An Introduction To Light Microscopy For Younger People and Beginners
by Mol Smith

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  The Microscope
Page 5

In addition to knowing the key points when purchasing a microscope for the first time, it is an advantage to understand a basic or 'starter' level microscope's parts. The microscope is focused using two controls: coarse adjustment and fine adjustment. The eyepiece lens compounded with the objective lens provides the power of magnification, so a 10x eyepiece and a 40x objective will magnify 400 times. A microscope may have 2, 3, or 4 objectives lenses mounted in a turret that turns. This allows for selection of different powers of magnification. Typical powers for objectives are x4, x10, x40, x100. Eyepieces are normally 5x, 10x or 20x. Most microscope retailers will offer eyepieces as accessories purchasable separately, except for the initial one provided with the microscope.

Lighting, both under and over versions, may have a control to adjust the intensity of light. The under-stage light is fixed focus on cheaper microscopes or sometimes can be adjusted by a cruder set of fixed apertures (holes in a disc). On slightly dearer microscopes, but still basic models,  focusing and manipulating the light beam is by means of an iris aperture and a substage condenser. Being able to adjust both the intensity and the focus of the light enables clearer and sharper viewing of a subject on a slide! Specimens are mounted on glass slides placed in the stage clips. On microscopes a little dearer than a starter microscope, the stage can be finely moved by two controls to allow easy viewing of all parts of a subject, or to follow (track)  swimming microscopic forms. Basic microscopes without a moving stage means moving the slide by hand - which is not very easy to do in a useful way, especially by young people.