Compound Microscopes

The historians to the Dutch spectacle maker, Zacharias Janssen, around the year 1590, credited the compound microscope. The compound microscope uses lenses as well as light to enlarge the image and is also called an optical or light microscope.  The simplest optical microscope is the magnifying glass and is good to about ten times magnification.  The compound microscope has two systems of lenses for greater magnification, first is the ocular, or eyepiece lens that one looks into and second is the objective lens, or the lens closest to the object.  Before purchasing or using a microscope, it is important to know the functions of each part. The eyepiece lenses are usually ten times or fifteen times power. Tube connects the eyepiece to the objectives lenses. Arm supports the tube and connects it to the base. Base is the bottom of the microscope and used for support. Illuminator is a steady light source used in place of a mirror. Stage is the flat platform where you place your slides. Revolving Nosepiece or Turret is the part that holds two or more objectives lenses and can be rotated to easily change power. Objective Lenses usually have 3 or 4 objectives lenses on a microscope. Rack stop is an adjustment that determines how close the objective lens can get to the slide. Condenser Lens is focusing the light onto the specimen. Condenser lens are most useful at the highest powers. Diaphragm or Iris has different sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide. There is no set rule regarding which setting to use for a particular power. To be able to focus your microscope, you need to start with the lowest power objectives lens first and while looking from the side, crank the lens down as close to the specimen as possible without touching it. If you look through the eyepiece and focus upward only until the image is sharp and you can’t get it in focus, repeat the process again. Once the image is sharp with the low power lens, you should be able to simply click in the next power lens and do minor adjustments with the focus knob. And if your microscope has a fine adjustment, turning it a bit should be all that’s necessary. Then continue with subsequent objective lenses and fine focus each time.