- the ability to distinguish closely spaced points as separate points.
- Resolution Limit
- smallest separation of points which can be recognized as distinct.
- Resolving Power
- resolution achieved by a particular instrument under optimum viewing conditions.
- the image must be properly focused, and
- the image must have adequate resolution
The left image shows low resolution and the right image shows high resolution. The left image is an enlargement of a low magnification image whereas the right image is taken at the higher magnification. Both images are of a cell nucleus (rat’s liver cell).
Magnification is simply the process of enlarging an image. Once a TEM is calibrated then it is possible to determine exactly how much enlargement has occurred. This can be recorded on an image as a scale bar. The use of ‘times magnification’, e.g. 50,000x, will only be accurate for an image of set/ fixed dimension and so can lead to errors.
Higher magnification will not necessarily give higher resolution. Unless a microscope is equipped to deliver higher resolution images, higher magnification will only achieve 'empty' images.
Resolution in a microscope is determined primarily by the wave nature of light or electrons according to Abbe's equation:
Illumination with a smaller wavelength results in better resolution (the two spots can be seen as distinct) and this is why the electron microscope produces higher resolution images than the light microscope; because the wavelength of an electron is smaller than visible light.
Illumination with a smaller wavelength results in better resolution.
|d||resolution (minimum resolvable distance)|
|λ||wavelength of the energy source|
|n||refractive index of the medium|
Note: The term nsinα is named numerical aperture.
For more on resolution see the Scanning Electron Microscope (SEM) module.