Current Help System: PC-DMIS Vision (View Core Help)

### Calibrate Optical Center

This procedure calibrates the optical center position of a zoom cell. The optical center is the point in the camera field of view where a feature does not move laterally as the cell zooms. This location information keeps the image view stable as the magnification is changed and minimizes measurement error between features at different magnifications. The optics hardware should be assembled so as to keep this location near the center of the field of view to allow maximum field of view utilization. The optical center calibration is to fine tune the position location is software. Note that it is desirable to measure related features at the same magnification. A zoom cell that changes magnification without a lateral shift in the image is said to be parcentric. A zoom cell that changes magnification without a change in focus is said to be parfocal.

No physical change takes place in the video camera or stage in any way. Any changes you make will appear only in the LIVE View of the Graphics Display window.

Note: Open the Probe Toolbox dialog box, select the Gage tab, and select the cross-hair gage before you begin to calibrate the Optical Center. This will display the cross-hair gage in the Live View.

To calibrate the optical center:

1. Select Calibrate Optical Center from the drop-down list on the Calibrate Vision Probe dialog box.

2. Click Calibrate. The Calibrate Optical Center dialog box is opened.

Calibrate Optical Center dialog box

3. Specify the Calibrated Center. PC-DMIS Vision supports any size of Video Frame, though the most common are 640 X 480 and 768 X 576 pixels. Edit the values in the X and Y Pixel boxes to adjust the position of the optical center of the video frame.

Caution: Your service technician has set the initial displayed values. If you make any physical changes to the optics or camera relative to the optics, the optical center values will need to be re-evaluated.

4. Click the button to go to the highest magnification level. With the lens completely zoomed in, you may need to adjust the lighting to see clearly.

5. Identify a small dust particle, and manually move the stage so the center of the cross hair coincides with the dust particle.

6. Click the button to go to the lowest magnification level. With the lens completely zoomed out, you may need to adjust the lighting to see clearly.

7. If the center of the Cross Hair does not coincide with the "dust", click the arrows in the Manually Moved Center area to align the Cross Hair with the "dust". After the “dust” is aligned, repeat steps 4 through 7.

8. When the result is acceptable (when there is no perceivable shift or the shift is less than one pixel when going from high magnification to low magnification), Click Calibrate to update the Calibrated Center values with the manually adjusted values.

9. Click Close when par-centricity has been established.