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Isara 400 CMM - asphere measurement results

The precision optics industry is moving towards increasingly complex optics design and aspheres are becoming an increasing percentage of manufactured optics. However the production and metrology of aspheres remains a challenge.

The German National Metrology Institute run High Level Expert Meetings at which this is addressed and comparisons made between measurement techniques. The Isara 400 coordinate measuring machine has been used to measure a 58 mm apherical lens for this meeting. A grid measurement was performed taking 3800 points at a grid spacing of 0.8 mm over a diameter of 54.5 mm. The measured form error, after subtraction of the theoretical asphere and correcting for radius deviation, is shown above.

Repeatability tests show the difference between three consecutive measurements is approximately 9 nm (2σ). Scanning measurements were performed across the centre line along the X and Y axes at 0,2/0,3 mm/sec and a sample frequency of 2 kHz. A repeatability 2σ<15 nm was achieved.

 

More info:  Isara 400 CMM;  traceable measurement uncertainty; soft materials for CERN