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Focus Test

The objective of the Focus test is to find the focus stepper motor value that brings the beams' focus to coincide with the plate surface. The focus stepper motor value depends on the type of plate, therefore, this test should be repeated for different plate types. It is recommended to perform the test for each plate type and plate thickness the customer intends to use.

1. Load the plate you intend to use for this test.
2. From the Brisque Launch pad, or from the Setup panel, double click the Calibration icon; the Lotem calibration window opens.
3. Choose Focus from the Calibration Type menu.
   


Figure 5-1: Lotem Calibration window - Focus test

4. The Current Plate type is automatically read from the PC Controller.
5. Unload policy:
• choose User request if you do not want the plate to automatically unload when the test is finished. This enables you to reuse the plate for additional calibration tests.
• choose Each test if you want the plate to automatically unload when the test is finished. In this case, you will need to load another plate for additional tests.
6. Image Offset: when the plate is used for several tests, you need to enter the position on the plate from which the current test is to begin. Enter the vertical and horizontal offset, in mm, from the upper left corner of the plate.
7. Plate thickness is automatically loaded from the PC controller, according to the plate currently loaded.
8. Intensity for test: enter the laser intensity to be used in the test. Recommended: 40% lower than the listed default value.
9. Focus value: the value listed is a default value or the last saved value.
10. Test focus values (steps): enter the desired test range for the stepper motor values. Recommended: enter a range of 100 - 300 motor steps.
11. Number of steps: enter the requested number of exposures in the above range of Test focus values. Minimum one step is 20.
12. Press Test to initiate the focus test according to the above setting.

Note: Press Get to load a previous focus test result from the PC controller.

13. The application performs several exposures, according to the settings in the above window.
14. When the exposure is completed, develop the plate and examine the results.
15. In the exposed batch, select the rectangle of the highest intensity. This rectangle is the lightest or darkest rectangle, depending on the plate type.
16. Mark the focus stepper motor value of the selected rectangle. This value is the optimal focus for the tested plate thickness.
17. Enter the above optimal focus value in the Focus value field of the Focus calibration window.
18. Press Save to save the new focus stepper motor value in the PC controller.
19. If required, repeat the test for other plate types and plate thickness values.
20. Press Exit to exit from this window, or continue to another calibration test.

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