AVR200 and AVR300 User Guide
8.3.1 Zoom Optics Parfocality and Focus
Definition
Parfocality is the condition in which the video image remains in focus as the magnification is adjusted from highest to lowest. Starrett zoom optics are designed to maintain parfocality throughout their magnification range. To check parfocality, always reference a flat, sharp edge. Do not select a rough or sloping feature. The magnification (Mag) checker provided with the system is an ideal part to check parfocality.
Procedure
To check parfocality, perform the following steps:
1. Place the MAG checker or other suitable inspection part on the stage and secure properly.
2. Backlight the image as necessary. Set light levels as needed to avoid blooming.
3. At low magnification, select a flat, sharp edge in the center of the field of view (FOV).
4. Select highest magnification, and carefully refocus the image by physically changing the viewing distance.
5. While observing the feature, slowly adjust the magnification lower. Verify that the feature remains focused as the magnification is lowered.
6. Report any observed discrepancy. If the error is verified, contact your Starrett representative for authorized service.
8.3.2 Zoom Optics Parcentricity
Definition
Parcentricity describes the condition where a feature remains at the optical center of the video image throughout the magnification range. Like parfocality, parcentricity requires that the feature be first located at highest magnification.
Procedure
To check parcentricity, perform the following steps:
1. Place the MAG checker or other suitable inspection part on the stage and secure properly.
2. Select the crosshair image tool and verify that it is at its defined center position. Refer to the MetLogix M3 Video and FOV Inspection Software User’s Guide for detailed information on centering the crosshair. The crosshair is to remain at this position during the parcentricity test. 3. Zoom to low magnification and adjust the stage position so that the crosshair is centered on the X-Y axis of the calibration standard (or another suitable feature if the standard is not used).
4. Change to high magnification and refocus the image.
5. Adjust the stage position as needed to recenter the crosshair on the feature.
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