Microscopes

Microscopy: The Instruments A compound microscope uses a series of lenses for magnification. Light rays pass through specimen and into objective lens (one of a series of objective lenses). Has one or two ocular lenses Total magnification = magnification of objective lens X magnification of ocular lens. Figure 3.1b

Principles of Light Microscopy Magnification is how much an image is enlarged under a microscope. Resolution is the amount of detail you can see in an image. You can enlarge a photograph indefinitely using more powerful lenses, but the image will blur together and be unreadable. Therefore, increasing the magnification will not improve the resolution. This is also known as the resolving power

Microscope parts and functions Arm - this attaches the eyepiece and body tube to the base. Base - this supports the microscope Body tube - the tube that supports the eyepiece; provides a passageway for light to travel Coarse adjustment –brings object into focus Diaphragm - an adjustable opening under the stage, allowing different amounts of light onto the stage. Eyepiece –contains the first of a series of lenses, the ocular lens, used to magnify an object. Fine focus adjustment –Allows resolution to be adjusted to provide clarity and more detail to the image seen.

Microscope parts and functions High-power objective – longest objective, contains a large lens with high magnifying power. Low-power objective – smallest of a series of lenses with a low magnifying power, contained in the shortest objective. Light source- this directs light upwards onto the slide through the stage opening. Revolving nosepiece - the rotating device that holds the objectives (lenses). Stage - the platform on which a slide is placed. Stage clips - metal clips that hold a slide securely onto the stage.

Focusing Specimens 1. Always start with the low power objective. Use the coarse adjustment knob to focus to bring the stage up. Do not use stage clips, try moving the slide around until you find something. Now switch to High Power. (If you have a thick slide, or a slide without a cover, do NOT use the high power objective). Use the fine adjustment knob to focus specimens. If the specimen is too light or too dark, try adjusting the diaphragm. 7. If you see a line in your viewing field, try twisting the eyepiece, the line should move, it’s a pointer, and is useful for pointing out things to your lab partner or teacher.

Making a Wet Mount 1. Gather a very thin slice/piece of whatever your specimen is. All samples should be paper thickness or thinner! 2. Place ONE drop of water directly over the specimen. 3. Place the cover slip at a 45 degree angle with one edge touching the water drop, and let go.

Making good drawings 100X nucleus All drawings must be in pencil. You may use colored pencils to show contrast. Draw a circle to represent your field of vision In the upper left hand corner of each circle include the specimen name as written on the slide label. In the upper right hand corner, include the magnification (100x or 430x). Label everything you identify! Cheek cell 100X Cell membrane nucleus

Measuring Using a Microscope

How to Measure Diameter Using Different Objectives Focus the metric ruler Line a mm marking with the left side of your f.o.v. Count the number of mm lines you see Estimate the fraction remaining This is your diameter for low (scanning) power Diameter 7.2mm=

Measuring Using a Microscope For medium or high power use the following mathematical formula to estimate the diameter. (scanning power/low power) x diameter of scanning (low power/high power) x diameter of low Remember these are estimates

Measuring the size of a cell Once you have your diameter for each objective calculated you can measure the size of a single cell. Count the number of cells that extend from one side of your F.O.V. and divide the diameter of the field of view you used by the number of cells you counted Example: .45 mm/20cells will tell you the approximate sixe of one cell when viewing 20 cells on high power Convert your answer to micrometers by multiplying by 1000 (1000 micrometers= 1mm)

Plant Cells

Bacteria

Bacteria