9.3 Zoom Optics Alignment Verification The performance of zoom optics (in zoom systems) should be verified regularly to ensure accurate measurements. Parfocality, parcentricity and squareness verifications are straight- forward and may be performed as often as desired. Focus is set during normal operation by changing the distance between the lens and the surface being viewed.
CAUTION: While optical alignment verification may be performed by an operator, optical alignment correction should only be performed by an authorized service technician. If alignment discrepancies are found, contact SKE or your local SKE representative to schedule authorized service.
9.3.1 Zoom Optics Parfocality & Focus Parfocality is the optical property which allows the video image to remain in focus as magnifi- cation is adjusted from highest to lowest. SKE 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 MAG checker available from Starrett Kinemetric is an ideal tool to check parfocality. Steps to check parfocality: 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 SKE representative for authorized service. 9.3.2 Zoom Optics Parcentricity Parcentricity is the optical property which allows a feature to remain 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. Steps to check parcentricity: 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. Please refer to the M3 manual for details 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 re-center the crosshair on the feature. 6. While observing the feature, slowly adjust the magnification lower. Verify that the feature remains at the center of the crosshair as the magnification is lowered. 7. Report any observed discrepancy. If the error is verified, contact your SKE representative for authorized service.
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