Light microscopy
This article examine the microscope.
Resolution
.[1]
Where:
- = resolving distance; smaller better.
- = numerical aperture of the objective; typically 0.25 - 1.4, >1.0 is oil immersion, it is usu. inscribed on the lens itself.
- = numerical aperature of the condenser.
- = wave length of light.
Closure of the condenser diaphragm results in a loss of resolution, i.e. R is larger.[1]
Numerical aperture
.
Notes:
- Larger 'D' is better.
- Larger NA = better.
f-number (N)
N = f/D.
Where:
- N = f-number.
- f = focal length.
- D = diameter of entrance pupil.
At infinity:
.
.
.
N ---> smaller number = larger opening.
Numerical aperature
NA = numerical aperature.[2]
.
Where:
- n = index of refraction, n = 1.0 for air.
- theta = half-angle of the max. cone of light
Lenses
- Most lens = 'achromats' -- only correct green.
- 'Apochromatic' lenses - correct all colours; very expensive.
Condenser
- Condenser -- large flattened lens beneath the specimen.
- Iris diaphragm.
- Condenser diaphragm --> incr. contrast for resolution ---- large dia. good resol. bad contrast?
- Field aperature diaphragm --> optical illumination.
- Condenser diaphragm --> incr. contrast for resolution ---- large dia. good resol. bad contrast?
- Iris diaphragm.
Kohler illumination
Rationale
- Maximize resolution. (???)
Procedure
- Any specimen on stage.
- Focus.
- Adj. field aperature (bottom) - to obscure periphery of field of view (FOV).
- Raise or lower condenser until field aperature diaphragm clearly focused.
- +/-Center 'field aperature diaphragm - using condenser centering screws.
See also
References
- ↑ 1.0 1.1 "Principles of Microscopy". http://www.life.umd.edu/CBMG/faculty/wolniak/wolniakmicro.html. Retrieved 21 January 2011.
- ↑ URL: http://en.wikipedia.org/wiki/Numerical_aperture. Accessed on: 21 January 2011.