Hitachi S-4800 manual Condenser Lens Setting and Image Quality

3.10.2Condenser Lens Setting and Image Quality

Probe current is adjusted by changing the Cond Lens 1 value.

To increase probe current, select a lower Cond Lens 1 value (larger spot size). Information necessary for setting of Cond Lens 1 is as follows.

(1) Resolution:

The electron beam size is smaller with a higher excitation value of Cond Lens 1. However, image resolution also depends on the S/N ratio of the image and on the ease of focusing and astigmatism correction.

(2) S/N ratio:

The signal to noise ratio is better with lower excitation values of Cond Lens 1.

(3) Charging:

Charging of insulator specimens is greater at smaller excitation values of Cond Lens 1.

(4) Signal source:

Generally the backscattered electron imaging needs higher probe current than the secondary electron imaging. X-ray analysis needs much higher probe current.

3.10.3Objective Lens Aperture Size and Image Quality

The objective lens aperture has four openings: 100, 50, 50 and 30 micrometers (numbered 1, 2, 3 and 4).

For normal operation, use number 2 or 3 (50 micrometers). The electron optical column of S- 4800 is designed to achieve highest resolution with 50 micrometers aperture.

When a larger probe current is required, for example X-ray analysis, use number 1 (100 micrometers). Resolution may degrade with this large aperture.

Use number 4 (30 micrometers) to reduce probe current, for example to reduce charging. Resolution is not improved but the depth of focus is better with the smallest aperture

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