8.3 Verifying Zoom Optics Alignment
The system’s zoom optics (if ordered) should be verified regularly to ensure accurate measurement. Parfocality, parcentricity, and squareness verifications are straightforward and can be performed as often as desired. Focus is adjusted as needed by changing the distance between the lens and the surface being viewed. Caution Optical alignment correction should only be performed by an authorized service technician. If alignment discrepancies are found, contact Starrett or your local Starrett representative to schedule authorized service.
8.3.1 Verifying Zoom Optics Parfocality and Focus
Definition
Parfocality is the condition in which the video image will remain 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. A magnification (mag) checker is an ideal part to check parfocality. Refer to “Spare Parts and Accessories” to order a mag nification checker from Starrett.
Procedure
To check parfocality, do the following:
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 Verifying Zoom Optics Parcentricity
Definition
Parcentricity describes the condition wherein a feature will 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.
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