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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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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.

Depth of focus

The vertical distance through which the sample can be moved without affecting the sharpness of the image. This will depend on the magnification.

Focused ion beam technology (FIB)

A high energy (typically 30kV) ion beam (typically gallium ions) is directed onto a hard sample and can be used for imaging or milling. Such a beam can be used in combination with the electron beam in a scanning (dual beam) electron microscope.

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 [