Lens-field center alignment for high resolution electron microscopy

In the objective lens alignment in transmission electron microscopy, there is usually some discrepancy between the incident beam directions required to satisfy the voltage-center condition or the coma-free condition. This is because an incident beam direction is found for the reference point conjugate to the screen center, while the reference point is usually not located along the lens-field axis. In this report it is demonstrated that the voltage-center alignment keeping the coma-free condition can be carried out by finding an object point on the lens-field axis. We propose to call this technique a lens-field center alignment. Since most microscopes have the deflector below the objective lens needed for this technique, the lens-field center alignment can be used in most microscopes.