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Glossary terms about Objective lens

Objective lens
The lens nearest to the specimen and used to focus the electron beam onto the specimen surface.

8 pages mention Objective lens

The BSD is mounted below the objective lens pole piece and centered around the optic axis. 
Electromagnetic lenses, apertures and beam size
The condenser lens is at the top and the objective lens at the bottom. 
Magnetic lens system
The condenser lens controls the intensity of the electron beam reaching the specimen. 
Recommended reading
Sample preparation
Magnetic materials can be investigated, but care is needed so that the powder is not attracted to the objective lens pole piece where it could disrupt the  
Spot size
A smaller objective lens aperture produces a smaller spot size. 
What is astigmatism?
An image is generally regarded as free of astigmatism when it does not streak in one direction or the other when the objective lens is adjusted to under or over focus at around 10,000X magnification. 
What is resolution?
NA is the numerical aperture of the objective lens