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Long Path Measurements


To measure the entire optical surface of a large optic, or an element with a long radius of curvature, the measurement system may need to be positioned far from the test piece—in some cases tens of meters away. Such a large cavity between the test and reference optics will almost inevitably lead to vibration and air turbulence that will significantly distort the measurement data.  Large scale airflow and temperature control systems can be prohibitively expensive or impractical over long measurement paths. Vibration is difficult to isolate in long path test setups as well.


4D’s PhaseCam dynamic laser interferometers are used by the world’s premier large optics manufacturers and telescope integrators to ensure excellent performance after installation. Their ability to measure optics despite vibration and to thrive in environments with significant turbulence makes PhaseCam laser interferometers perfectly adapted to long stand-off measurements without vibration isolation.

Added Technical Resources

Measuring Large Mirrors With Secondary and Tertiary Support Structures

Challenges of measuring a mirror or system that is partially obscured by structural members. This app note demonstrates an original method of acquiring contiguous data of the surface(s).


Measuring Transmitted Wavefront Error with the FizCam 2000

A new technique for vibration-insensitive measurement of transmitted wavefront error (TWE) improves repeatability by more than 7X.

Products for Measuring Long Path Optics


Vibration-immune metrology for convex and aspheric optics, from millimeters to meters in diameter.

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(520) 294-5600


3280 E Hemisphere Loop, Ste 146
Tucson, AZ 85706


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