Electron Microscopy
How to correct astigmatism in electron microscopy
The best procedure of correcting astigmatism is by setting X and Y stigmators to zero offset. This is followed by fine focusing the sample in the best possible way. The process advances by adjusting either X or Y stigmators control. It is important not to adjust both controls. The process of adjusting the controls is aimed at attaining the best image and refocusing the image. After obtaining the best image with one stigmator, the other stigmator will be used in getting the sharpest possible image. A process of refocusing the image follows this. It will be possible to notice that the astigmatism has been corrected when there will be no streaking of image during the focusing process (Spence, 2013).
What differences can magnification do to effect the electron microscopy photo? Explain what is in focus – over focus and under focus and how it can happen due to change in magnification in electron microscopy
Magnification in the use of microspores focuses on the extent to which an image under a microscope can be enlarged. The quality of an electron microscopy photo is dependent on the resolution of the microscope. Resolution entails the details that can be seen in an image. It is possible to enlarge a photo indefinitely using powerful microscope lenses. However, the resulting image will be blurry and unreadable. This means that an increase in the level of magnification does not improve the resolution of an image. Magnification from a Scanning Electron Microscope (SEM) affects the electron microscopy photo by producing a three dimensional image of a sample. This is made possible by bouncing electrons off and detecting them using multiple detectors. SEM is effective in the production of high quality microscopy photos because it has a magnification of about *100000 (A Guide to Scanning Microscope Observation, JEOL).
Over focus occurs when the knob of an electron lens is turned clockwise to be above the focal position. Under-focus is when the knob is turned in an anticlockwise manner to be below the focal point. In focus occurs when the specimen is in the same position relative to the lenses. This allows the lenses to focus the beams into a crossover at a point closer to the lens. In electron microscopy, the focusing effect increases with the strength of the magnetic field, this is controllable using the current flowing through the coils (A Guide to Scanning Microscope Observation, JEOL).
What are the advantages of using tomography in electron microscopy in analyzing photo data?
Electron tomography provides an intermediate level between the high resolution offered by the existing averaging methods of analyzing photo data and the lower resolution that is provided by the serial thin section reconstruction (McEwen et al, 2007).
Electron tomography also provides a useful technique of studying irregular cellular structures using moderately high resolution. An additional advantage of this approach to analyzing photo data is that it provides a three dimensional reconstruction methodology where three-dimensional volume can be computed from a series of projection images captured from a range of tilt angles. While providing a better and greater depth resolution, electron tomography can avoid the mechanical limitation defining how thin a specimen can be cut. An additional advantage is that electron tomography does not require the occurrence of a specimen as multiple copies of an identical design (McEwen et al, 2007).
Being the most applicable methodology of obtaining three-dimensional information by electron microscopy, electron tomography facilitates effective investigation of polymorphic structures at high resolution. Through electron tomography, it is possible to provide a complete molecular resolution three-dimensional mapping of cellular proteomes that include detailed interactions (McEwen et al, 2007).

References
A Guide to Scanning Microscope Observation, JEOL.
McEwen, B., Dong, Y & VandenBeldt, K. (2007). Using Electron Microscopy to Understand
Functional Mechanisms of Chromosome Alignment on the Mitotic Spindle. Methods in Cell Biology.
Spence, J. C. H. (2013). High-resolution electron microscopy. Oxford : Oxford University Press