Microscopes Anton van Leeuwenhoek and his Microscope

Parts of the Microscope ocular stage objective lens rotating nose piece condenser light source fine adjust course adjust head arm base mechanical stage mechanical stage controls Power switch and light control locations vary.

How an image is formed by a microscope

Working distance Working distance is the distance between the specimen and the magnifying lens.

Depth of field Depth of field is a measure of the amount of a specimen that can be in focus.

Magnification Magnification is a ratio of the enlargement (or reduction) of an image (drawing or photomicrograph), usually expressed as X1, X1/2, X430, X1000, etc.

Magnification and resolution are terms used frequently in the study of cell biology, often without an accurate definition of their meanings.

Resolution Resolution is the ability to distinguish between two points. Generally resolution increases with magnification, although there does come a point of diminishing returns where you increase magnification beyond added resolution gain.

How an image is formed by a microscope

How the image appears

Determining field size As the total magnification goes up, field size gets smaller. You can measure field size directly at low magnification. However, at higher magnification you won’t have a sufficiently precise measuring instrument. So then what? You can calculate field size from what you know about the relationship between field size and magnification.

Calculating field size Diameter of field A (known from direct measurement) X Total magnification of field A = diameter of field B (this is the unknown) X total magnification of field B You can rearrange the terms to produce the following equation: diameter of field A X total magnification of field A = diameter of field B total magnification of field B Therefore: If field A = 2 mm in diameter at 50X total magnification And the total magnification of field B = 100X then Diameter field B = 2 X 50 = 100 = 1 mm

But, there is another way! The diameter of the field is inverse to the magnification! (see slide11) What this means is that if you increase the magnification by say a factor of four (four times), the field size will decrease by the same factor. Example: The field diameter at 100X is 2 mm. Go from 100X to 400X, an increase of 4 times. The field diameter is decreased 4 times. (Simply divide by 4!) 2 mm = 0.5 mm 4

Illustrations of microscope observations Drawings of specimens observed under the microscope should always include the following: Title Total magnification Labels of interesting features

Example of a proper illustration Epithelial cells from a cheek Total magnification - 400X nucleus plasma membrane

Parts of the Microscope This is the model of scope used in JH 219

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