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Glossary terms about Focus

Focus
In scanning electron microscopy: The process of bringing the electron beam to its smallest diameter cross section at the sample surface. The production of a sharp, well defined image, rather than a fuzzy, blurry image.

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22 pages mention Focus

Astigmatism
There are a variety of factors which contribute to form an astigmatism, which distort the image by an amount rast =βΔf, where Δf is the maximum difference in focus induced by astigmatism. 
Background information - What is transmission electron microscopy?
The TEM reveals levels of detail and complexity inaccessible by light microscopy because it uses a focused beam of high energy electrons. 
Electron column
A set of binoculars is attached to the column and can be swung around to focus on a small, movable screen within the chamber. 
Focus/stigmation
Micrograph quality is affected by aperture size, focus, stigmation, and use of image collection software. 
Frequently asked questions
Step-by-step procedures for using TEMs  
Image capture
The binoculars are available for focusing the image. 
Image formation basics
This scattered radiation passes through an objective lens, which focuses it to form the primary image. 
Imaging mode setup
For bright and dark field imaging, it is necessary to adjust the objective lens (focus knob) to produce a crisp image of what is in the plane of the sample (specimen). 
Object/Image planes
The focal plane of the lens is where parallel rays are brought to a focus
Organic sample/physical science specimen preparation for TEM
 
Pole-pieces and Coils
The strength of the field in a magnetic lens controls the ray paths, bringing off axis rays back to focus
Problems with lenses: aberrations
Astigmatism affects the ability to focus an image but is totally correctable. 
Resolution
 
Spherical aberration
Images left of the center column are defocused toward the inside, images right are defocused towards the outside. 
The diffracted beam
These waves interact constructively and are brought to focus at the back focal plane of the objective lens (see  
The Eucentric Position
TEMs are set up so that magnification, camera length, and correct focus are set to this reference position. 
Theory of TEM image generation
 
Using the JEM-1010 Transmission Electron Microscope for physical science material
Use focus knob on x16 (right hand console) to adjust the number. 
Using the JEM-1010 Transmission Electron Microscope for thin resin sections of biological material
Use focus knob on x16 (right hand console) to adjust the number. 
Virtual TEM - Basic imaging
Sample insertion videos:  
Virtual TEM - Diffraction and advanced imaging
Sample insertion videos:  
What content is right for me?
how to use the apertures (both the condenser and objective) to enhance contrast [see Virtual TEM]. how to operate the controls to adjust focus and correct for stigmation [