Optical Microscope Flashcards
What is absorption ?
When light passes through an object the intensity is reduced depending upon the colour absorbed. Thus the selective absorption of white light produces coloured light.
Refraction
Direction change of a ray of light passing from one transparent medium to another with different optical density. A ray from less to more dense medium is bent perpendicular to the surface, with greater deviation for shorter wavelengths
Diffraction
Light rays bend around edges - new wave fronts are generated at sharp edges - the smaller the aperture the lower the definition
Dispersion
Separation of light into its constituent wavelengths when entering a transparent medium - the change of refractive index with wavelength, such as the spectrum produced by a prism or a rainbow
Routes of Light
1. Light source •2. Illuminator (light source) •3. Condenser •4. Iris diaphragm •5. Specimen (on stage) • 6.Objective lens • 7.Body tube • 8.Ocular lens (eye piece)
What is the role or what does the iris diaphragm do ?
The iris diaphragm controls how much light enters the specimen.
So if more light enters the specimen , there will be less contrast will be observed leading to less detail to be seen .
What is the role of the condenser ?
The condenser emits light as parallel beams to reduce scattering .
for fine tuning, you may want to lower the condenser slightly under oil immersion
What does the mechanical stage do ?
that allows us to adjust the position of the specimen without touching the slide
Resolution
Resolution is the ability to see two items as two separate things, i.e., two dots as two separate dots
The resolution a microscope is capable of achieving is the smallest distance between two dots such that the two dots may be observed (resolved) as separate entities
Coarse adjustment Knob
The coarse adjustment knob elevates the microscope’s stage up and down quickly
Fine adjustment Knob
the fine adjustment knob should require more revolutions to elevate the stage as much as the coarse
Magnification
Should always be 10X
means the process of magnifying something, usually visually. It also means the magnifying power of an instrument such as a microscope
An object can be focused generally no closer than 250 mm from the eye (depending upon how old you are!)
Objective Turret
holds the objective lenses.
What does the Resolution ?
The higher the NA (numerical aperture) the greater the resolution
– (a) Another thing that can influence resolution (in addition to wavelength and numerical aperture) is refraction
– (b) The occurrence of refraction causes objects to appear fuzzy (i.e., lowers resolution)
– (c) To achieve high resolutions under high magnification, refraction must be minimized
– (d) To do this, one employs immersion oil between objects and lenses
Immersion Oil Index Reraction
the speed with which light passes through a substance) that is identical to that of glass, with both different from that of air
When light passes from a glass slide into air, the light bends; this bending causes a scattering of the light exiting a specimen so consequently there is a reduction in resolution (i.e., there is an increase in fuzziness)
What does the immersion oil do when it posses the same index of refraction ?
Because immersion oil possesses the same index of refraction as glass, light passing out of a specimen and slide will pass through the oil without bending and then will go directly into the immersed lens
How does Focusing work?
focused by moving the objective lenses up and down rather than moving the stage up and down
Light source how is it controlled ?
One controls the level of illumination of an object at the light source
• The level of contrast, on the other hand, is controlled using the iris diaphragm (which also impacts the level of object illumination)
What is a compound Microscope ?
A compound light microscope employs at least two lenses through which light passes going from the specimen to the eye
• Compound light microscopes can be monocular or binocular (one eye piece or two, respectively; we will use binocular scopes exclusively)
Light Microscope
Light microscopy is the use of light as the substance that passes through the specimen (i.e., contrast to electron microscopy)
