light microscopy Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of micr ...

, a water immersion objective is a specially designed

objective lens In optical engineering, the objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image. Objectives can be a single lens or mirror, or combinations of several optical elem ...

used to increase the

resolution Resolution(s) may refer to: Common meanings * Resolution (debate), the statement which is debated in policy debate * Resolution (law), a written motion adopted by a deliberative body * New Year's resolution, a commitment that an individual ma ...

of the microscope. This is achieved by immersing both the lens and the specimen in water which has a higher

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, o ...

than air, thereby increasing the

numerical aperture In optics, the numerical aperture (NA) of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light. By incorporating index of refraction in its definition, NA has the propert ...

of the objective lens.

Applications

Water immersion objectives are used not only at very large magnifications that require high resolving power, but also of moderate power as there are water immersion objectives as low as 4X. Objectives with high power magnification have short

focal length The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative foca ...

s, facilitating the use of water. The water is applied to the specimen (conventional microscope), and the stage is raised, immersing the objective in water. Sometimes with water dipping objectives, the objective is directly immersed in the solution of water which contains the specimens to look at. Electrophoretic preparations used in the case of

comet assay A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are ...

can benefit from the use of water objectives. The refractive index of the water (1.33) is closer to those of imaged materials or to the glass of the cover-slip, so more light will be collected/focused by this type of objective comparing to air-immersion ones, leading to a range of higher numerical apertures (NA).

Correction collar

Unlike oil, water does not have the same or near identical refractive value as the cover slip glass, so a correction collar is needed to be able to variate for its thickness. Lenses without a correction collar generally are made for the use of a 0.17 mm cover slip or for use without a coverslip (dipping lens).

References

{{DEFAULTSORT:Water Immersion Objective Microscopy

Applications

Correction collar

See also

References