Product

• Lotem^® 400
• Lotem 400 Xpose
• Lotem 200K

Background

The objective of the Focus test is to find the focus stepper motor value that enables the focus of the beams to coincide with the plate surface.

To verify that the calibrated focus value is correct, expose the SDT file from Brisque and examine the plate, see Scitex Digital Target (SDT). If the focus value is not correct, perform the focus test procedure.

Procedure

Before performing the focus test, disable edge detection.

Note: The focus stepper motor value is dependent on the plate type, so repeat this test for each plate type and thickness that the customer uses.

1. Load a plate.
2. Open the Lotem Calibration dialog box:
• For Lotem 400 Xpose—on the Xpose Utilities panel, double-click LotemCalib.
• For Lotem 400—proceed as follows:
1. In Brisque, from the Launch Pad, open the Setup panel, and then double-click Devices.
2. In the Output Device Handling dialog box, in the Device section, select Plate Setter > Lotem > Lotem400.
3. In the Operations section, select Lotem Calibration.
3. In the Lotem Calibration dialog box (example shown for Lotem Xpose), in the Calibration Type box, select Focus. The Current Plate type and Plate Sensitivity parameters of the plate that you loaded are automatically transferred from Lotem Controller.
   
4. Define the Plate Policy:
• Load plate—Automatically loads a new plate before the test begins. If you clear this option, you can reuse the plate for additional calibration tests.
• Unload plate—Automatically unloads the plate after the test. If you clear this option, you can reuse the plate for additional calibration tests.
5. Define the Image offset values:
   
• Horizontal offset—The value around the drum in mm
• Vertical offset—The value along the drum in mm
If you use the same plate for several tests, define different offset values for each test.
Note: The (0,0) offset coordinate is located at the upper-left corner of the plate.
6. In the Intensity for Test box, type the laser intensity.
   Note: It is recommended to use a value 40% lower than the listed default value.
7. In the Focus value box, type the default value or the last-saved value.
8. In the Test Focus Values [steps] area, type the test range for the stepper motor values in the From and To boxes.
   Note: The recommended range is 100–400 motor steps.
9. In the Number of Steps list, select the number of exposures in the test focus value range. The recommended minimum number of steps is 10.
   The Lotem Controller application automatically calculates the size of each step interval.
   Size of step = (To - From)/(Number of Steps -1)
   This interval is displayed in the Size box.
   Note: The interval value cannot be modified. It is intended to be a quick reference for the platesetter operator.
10. Click Test to initiate the focus test. The application performs several exposures.

Note: The Get button enables you to load a previous focus test result from Lotem Controller.

11. When the exposure is completed, develop the plate and examine the results.
12. In the exposed batch, select the target with the highest exposure (the lightest or darkest target, depending on the plate type), and note the focus stepper motor value of the selected target.
13. In the Calibration - Focus Calibration dialog box, in the Focus Value box, type the focus stepper motor value of the selected target. This value is the optimal focus for the tested plate thickness.
14. Click Save. The focus stepper motor value is automatically transferred to Lotem Controller.
15. If required, repeat the test for other plate types and thicknesses.

See also

Technical contact(s)

Content owner: Mario Amir
See the Escalation page for escalation contacts.

Date submitted

09 Nov 2003