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Difference between revisions of "Light microscopy"
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Closure of the condenser diaphragm results in a loss of resolution, i.e. R is larger.<br> | Closure of the condenser diaphragm results in a loss of resolution, i.e. R is larger.<br> | ||
<math>R = 1.22 * {gamma \over ( D/2*f )}</math> | <math>R = 1.22 * {gamma \over ( D/2*f )}</math>. | ||
Notes: | Notes: | ||
*Larger 'D' is better. | *Larger 'D' is better. | ||
*Larger NA = better | *Larger NA = better. | ||
f-number (N) | f-number (N) | ||
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At infinity: | At infinity: | ||
N = 1/(2*NA_i) | N = 1/(2*NA_i). | ||
f/D = 1/(2*NA_i) or 2*NA_i=D/f | f/D = 1/(2*NA_i) or 2*NA_i=D/f. | ||
N ---> smaller number = larger opening | N ---> smaller number = larger opening. | ||
==Numerical aperature== | ==Numerical aperature== | ||
http://en.wikipedia.org/wiki/Numerical_aperture | NA = numerical aperature.<ref>URL: [http://en.wikipedia.org/wiki/Numerical_aperture http://en.wikipedia.org/wiki/Numerical_aperture]. Accessed on: 21 January 2011.</ref> | ||
NA = n*sin(theta) | <math>NA = n*sin(theta)</math>. | ||
Where: | Where: | ||
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*theta = half-angle of the max. cone of light | *theta = half-angle of the max. cone of light | ||
Most lens | ==Lenses== | ||
' | *Most lens = 'achromats' -- only correct green. | ||
*'Apochromatic' lenses - correct all colours; very expensive. | |||
==Condenser== | ==Condenser== | ||
*Condenser -- large flattened lens beneath the specimen | *Condenser -- large flattened lens beneath the specimen. | ||
**Iris diaphragm | **Iris diaphragm. | ||
***Condenser diaphragm --> incr. contrast for resolution ---- large dia. good resol. bad contrast? | ***Condenser diaphragm --> incr. contrast for resolution ---- large dia. good resol. bad contrast? | ||
****Field aperature diaphragm --> optical illumination. | ****Field aperature diaphragm --> optical illumination. | ||
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#Focus. | #Focus. | ||
#Adj. field aperature (bottom) - to obscure periphery of field of view (FOV). | #Adj. field aperature (bottom) - to obscure periphery of field of view (FOV). | ||
#Raise or lower condenser until field aperature diaphragm clearly focused | #Raise or lower condenser until field aperature diaphragm clearly focused. | ||
#+/-Center 'field aperature diaphragm - using condenser centering screws | #+/-Center 'field aperature diaphragm - using condenser centering screws. | ||
==See also== | |||
*[[Basics]]. | |||
*[[Microphotography]]. | |||
==References== | ==References== | ||