Introduction to the Microscope

an optical instrument used for viewing very small objects, such as mineral samples or animal or plant cells, typically magnified several hundred times. 1665 - Robert Hooke (1635-1703)- book Micrographia, published in 1665, devised the compound microscope most famous microscopical observation was his study of thin slices of cork. Named the term “Cell”.

Eyepiece Lens: the lens at the top that you look through Eyepiece Lens:  the lens at the top that you look through.  They are usually 10X or 15X power.  Eye piece Tube:  Connects the eyepiece to the objective lenses Arm:  Supports the tube and connects it to the base Base:  The bottom of the microscope, used for support Illuminator/Light:  A steady light source (110 volts) used in place of a mirror.  If microscope has a mirror, it is used to reflect light from an external light source up through the bottom of the stage. Stage:  The flat platform where you place your slides.  Stage clips hold the slides in place.  If microscope has a mechanical stage, it will be able to move the slide around by turning two knobs.  One moves it left and right, the other moves it up and down.

Objective Lenses:  Usually 3 or 4 objective lenses are present on a microscope.  They almost always consist of 4X, 10X, 40X and 100X powers.  When coupled with a 10X (most common) eyepiece lens, we get total magnifications of 40X (4X times 10X), 100X , 400X and 1000X.  Oil Immersion Lens:  An objective lens (usually 100X or greater) designed to work with a drop of special oil placed between it and the slide.  With oil, an increase in resolution will be noticed.    Also, see "Immersion Oil" above. Revolving Nosepiece or Turret:  This is the part that holds two or more objective lenses and can be rotated to easily change power. Diaphragm or Iris:  Many microscopes have a rotating disk under the stage.  This diaphragm 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.  Condenser: A simple device that condenses and focuses the light coming from the light source. The user can adjust a moveable Condenser, whereas one that is not moveable has a fixed focus. 

How to Focus Your Microscope:  The proper way to focus a microscope is to start with the lowest power objective lens first and while looking from the side, crank the lens down as close to the specimen as possible without touching it.  Now, look through the eyepiece lens and focus upward only until the image is sharp.  If 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.  If your microscope has a fine focus adjustment, turning it a bit should be all that's necessary.   Continue with subsequent objective lenses and fine focus each time. 

Immersion Oil:  A special oil used in microscopy with only the 100X objective lens (usually at 1000X total power).  A drop is placed upon the cover slip and the objective is lowered until it just touches the drop.  Once brought into focus, the oil acts as a bridge between the glass slide and the glass in the lens (the medium ).  This concentrates the light path and increasing the resolution of the image.

Magnification Your microscope has 3 magnifications: Scanning, Low and High. Each objective will have written the magnification. In addition to this, the ocular lens (eyepiece) has a magnification. The total magnification is the ocular x objective

Compound Microscope Dissection Microscope Scanning Electron Microscope (SEM) Transmission Electron Microscope (TEM)

Compound Microscope Compound microscopes are light illuminated. The image seen with this type of microscope is two dimensional. This microscope is the most commonly used. You can view individual cells, even living ones.

Compound Microscope Paulownia Wood c.s. 200x Frog’s blood 1,000x

Dissection Microscope A dissection microscope is light illuminated. The image that appears is three dimensional. It is used for dissection to get a better look at the larger specimen. (also called stereo microscope)

Sunflower with moth in the stem Dissection Microscope Head of a moth Sunflower with moth in the stem

Electron Microscopy Uses electrons instead of light. The shorter wavelength of electrons gives greater resolution. There are two types of electron microscopes: Transmission electron microscope Scanning electron microscope.