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Difference between revisions of "Light microscopy"
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*<math>R</math> = resolving distance; smaller better. | *<math>R</math> = resolving distance; smaller better. | ||
*<math>NA_{obj}</math> = numerical aperture of the objective; typically 0.25 - 1.4, >1.0 is oil immersion, it is usu. inscribed on the lens itself. | *<math>NA_{obj}</math> = numerical aperture of the objective; typically 0.25 - 1.4, >1.0 is oil immersion, it is usu. inscribed on the lens itself. | ||
*<math>NA_{cond}</math> = numerical | *<math>NA_{cond}</math> = numerical aperture of the condenser. | ||
*<math>gamma</math> = wave length of light. | *<math>gamma</math> = wave length of light. | ||
It follows from the above equation that, closure of the condenser diaphragm results in a loss of resolution, i.e. R is larger.<ref name=pom/><br> | |||
Stated differently:<ref>URL: [http://www.microbehunter.com/2008/12/18/the-condenser-aperture-diaphragm/ http://www.microbehunter.com/2008/12/18/the-condenser-aperture-diaphragm/]. Accessed on: 21 January 2011.</ref> | |||
*Opening the condenser --> increases resolution & brightness -- but -- decreases depth of field (DOF) & contrast. | |||
*Closing the condenser --> increases DOF & contrast -- but -- decreases resolution & brightness. | |||
===Numerical aperture=== | ===Numerical aperture=== | ||
NA = numerical aperature. | |||
General formula for NA:<ref>URL: [http://en.wikipedia.org/wiki/Numerical_aperture http://en.wikipedia.org/wiki/Numerical_aperture]. Accessed on: 21 January 2011.</ref><br> | |||
<math>NA = n*sin(theta)</math>. | |||
Where: | |||
*n = index of refraction, n = 1.0 for air. | |||
*theta = half-angle of the max. cone of light | |||
===NA and f-number=== | |||
N = f/D. | N = f/D. | ||
Where: | Where: | ||
*N = f-number. | *N = f-number, e.g. f 1.2, f 1.4, f 11. | ||
**Smaller N = larger opening. | |||
*f = focal length. | *f = focal length. | ||
*D = diameter of entrance pupil. | *D = diameter of entrance pupil. | ||
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<math>N = 1/(2*NA_i)</math>.<br> | <math>N = 1/(2*NA_i)</math>.<br> | ||
<math>f/D = 1/(2*NA_i)</math>.<br> | <math>f/D = 1/(2*NA_i)</math>.<br> | ||
<math> | <math>2*NA_i = D/f</math>. | ||
====Numerical aperture==== | |||
If one substitutes the above into the equation at the top:<br> | |||
<math>R = 1.22 * {gamma \over ( D/2*f )}</math>. | |||
Notes: | |||
*Larger 'D' is better. | |||
*Larger NA = better. | |||
* | |||
==Lenses== | ==Lenses== | ||