Microscope Flashcards
Important Features of Objectives
Focal point
•Working distance
•Resolving power / Resolution
•Numerical aperture
•Parfocal
- a measure of its ability to gather light and resolve fine specimen detail at a fixed object distance; a number that expresses the ability of a lens to resolve fine detail in an object being observed
numerical aperture
the ability of a microscope to stay relatively in focus as the user switches among the objectives
parfocal
the distance between the front of the microscope objective lens and the surface of the specimen or slide coverslip at the point where the specimen is completely in focus. As a general rule working distance decreases and total magnification increases due to the higher numerical apertures associated with high power objectives
working distance
the ability of a microscope to distinguish details of a specimen or sample; the smallest distance between two points on a specimen that can still be distinguished as two separate entities
resolution
principal focus of the lens
focal point
Passes light directly through specimen; unless cell is naturally pigmented or artificially stained,
image has little contrast.
Brightfield (unstained specimen).
Staining with various dyes enhances contrast, but most staining procedures require that
cells be fixed (preserved).
Brightfield (stained specimen).
Shows the locations
of specific molecules in the cell. Fluorescent substances absorb short- wavelength, ultraviolet radiation and
emit longer-wavelength, visible light. The fluorescing molecules may occur naturally in the specimen but more often are made by tagging the molecules of interest with fluorescent
molecules.
Fluorescence.
Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining living,
unpigmented cells.
Phase-contrast.
Like phase-contrast microscopy, it uses optical modifications to exaggerate
differences in density.
Differential-interference-contrast (Nomarski).
Uses lasers and special optics for “optical sectioning.” Only those regions within a narrow depth of focus are imaged. Regions above and below the selected plane of view appear black rather than blurry. This microscope is typically used with fluorescently stained specimens, as in
the example here.
confocal
What is a Microscope
•An OPTICAL instrument used to observe tiny objects, often objects that cannot be seen at all with the unaided human eye
Commonly used in a wide variety of laboratory applications as the
standard microscope; produces an image on a bright background.
brightfield
Increases contrast without staining by producing a bright image on a darker background; especially useful for viewing live
specimens.
darkfield
