Product

• Kodak^® Lotem^® 400 FH family
• Kodak Magnus^™ 400 LDA family
• Kodak Magnus 400 II LDA family

Background

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

The focus stepper motor is installed on the carriage and moves the lens tube back and forth according to the thickness of the plate mounted on the drum.

Prerequisites

Preload properly adjusted

Tools

• Densitometer
• Microscope
• Plates

Procedure

The focus stepper motor value is according to plate type. Perform the focus calibration test procedure for each plate type and thickness that the customer uses.

1. Load a plate.
2. From the Kodak Xpo^™ palette, select Tools > Calibration.
   Note: The Plate Thickness parameter of the loaded plate is automatically transferred from the Lotem/Magnus 400 Controller software.
   
   
   
   
3. In the Calibrate dialog box, perform the following steps:
   1. In the Calibration Type list, select Focus.
   2. In the Intensity for Test field, enter a relatively low intensity value—for example, 110.
      Note: The higher the intensity, the more difficult it will be to visually differentiate between the test strips and select the best focus. To obtain best results, start with a value that is 40% lower than the default value.
   3. In the Focus Value field, do not change this value until the optimal focus value has been determined.
      Note: To load the last-saved focus test value, click Get.
   4. In the Test Focus Values [steps] area, in the From and To fields, type the test range for the focus stepper motor values. For example, on 0.3-mm thick plates, enter a range between 150 and 200 motor steps.
   5. In the Number of Steps list, select the number of exposures to perform for the selected test focus value range. For best results, enter a minimum of 10 steps.
      When you type a step value, the Lotem/Magnus 400 Controller software automatically calculates and displays the size of each step interval in the Size field, using the following formula:
      Step size = (To–From)/(Number of steps –1)
      
   6. In the Resoluton list, select the resolution used by the customer.
   7. In the Test File list, select the TIF file that you want to use for the focus test.
      Note: Test files are predefined; the ones that appear in the list are according to the selected resolution.
   8. In the Current Plate list, select the plate size that you are using for the test.
   9. In the Image Offset fields, type a value in millimeters for the horizontal offset (around the drum), and the vertical offset (along the drum).
      Note: The (0,0) offset coordinate is located at the upper-left corner of the plate.
      If you use the same plate for multiple tests, enter the appropriate offset values for each test.
   10. In the Plate Policy section, select or clear the Load and Unload check boxes that apply to focus test:
       • Load: Automatically loads a new plate before the test begins. To perform multiple calibration tests on the same plate, before you start the next test, clear this check box to reuse the plate.
       • Unload: Automatically unloads the plate after the test. To perform multiple calibration tests on the same plate, before you start the next test, clear this check box.
4. Click Test to start the focus test.
   Lotem/Magnus 400 Controller performs a series of exposures on the plate, after which you need to process the plate and examine the results.
   
5. From the batch of exposed target strips, select the best strip:
   • For positive plates (blue), select the clearest strip with the lowest density.
   • For negative plates (green), select the clearest strip with the highest density.
     
     
     

6. In the Focus Value field, type the optimal focus stepper motor value, and click Save.
   Note: If required, repeat the test for other plate types and thicknesses.

Technical contact

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

Date submitted

11 Jun 2008