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Microscope
a hollow tube with a lens at the top and bottom
an optical instrument that uses lens to bend visible light in order to produce a magnified image of a very small object with enhanced contrast and resolution
Janssen’s Microscope
Zacharias Janssen, 1585, earliest compound microscope, 20x-30x
improved by Hooke, coined the term “cell”
Leeuwenhoek Microscope
1974, Dutch scientist, a draper who taught himself microscopy to inspect fabrics, simple microscope, 200x, living cells “animalcules in pond water, discovery of bacteria, blood cells, and other microorganism
How magnification works?
the larger an object is the greater the angle at which light rays enters the eye and subtends on the retina gets larger
similarly an object brought closer to the eye appears larger because the angle at which the light rays enters the eye and subtends on the retina gets larger
Microscope lens
the lens of a microscope increases the angle at which the light rays from the object enters the eyes
Types of microscopes
simple microscope
compound microscope (Polarized light microscope, comparison microscope)
stereo microscope
Simple microscope
a magnifying glass made from a single convex lens that magnifies 5-10x
one level of magnification
produces virtual image
Compound Microscope
2 lens system that produce 2 levels of magnification, an objective lens above the sample projects a magnified image of the sample into the body tube (intermediate image plane), an ocular lens (eyepiece) near the eye further magnifies the image projected by the objective
higher magnification 40x-1000x, higher resolution
types of Compound Microscopes
polarized microscopes, comparison microscopes, phase contrast microscopes, fluorescence microscopes
Polarized Light Microscope
a special type of high power compound microscope, contains 2 polarizers- a circular rotating stage- and slots for compensators, most useful and versatile, can examine physical characteristics and optical properties, indentification of the item
Comparison Microscope
2 high power compound microscopes joined together with an optical bridge, allows simultaneous viewing of the left and right microscopes, used to compare microscopic items (Q and K) side by side in a circular field that is equally divided into two parts
PLM and Comparison microscopes
requires some sample preparation or mounting in oils, not the RI of the medium
Stereo Microscopes
consists of 2 separate, low power, monocular compound microscopes (one for each eye) w/ in 1 housing
each objective lens is offset by 15 degrees and produces a different image of the object, therefore each eye simultaneously sees the sample from a different perspective (separate image)
the 2 different images are combined to produces a stereoscopic, 3D image (similar to our eyes)
used for screening and sorting, gross class characteristics, preliminary identification (classification) and physical matching examination
provides a greater field of view and greater working distance and greater depth of field
Types of stereo microscopes
Greenough- 2 identical and symmetrical optical systems, contains separate eyepiece and objective in a single housing, lower price
Common Main Objectives- single large objective that is shared between a pair of ocular tubes and lens system, enables longer working distance and continuous zoom system, modern design, most common type
Microscopes V.S. High Power Compound Microscopes
Stereo microscopes have two (2) identical path offset from one
another to mimic the natural offset of the two eyes; produce a 3D
image
– Usually used first for examining evidence
– Use for screening, viewing and locating samples
– No sample preparation
– Provides an upright, unversed, 3D image
– Greater field of view, working distance and depth of field
– True colors with Rx light
High Power Compound Microscopes have one (1) optical path that
is split at the oculars to give the same left and right images
– Produces a 2D image
– Reversed image
– Higher magnification and resolution