Parabola in Autocollimation

Optical Setups

Overview

The surface quality of off-axis parabolas and fast parabolas can be verified in an autocollimation setup. This setup is useful when space constraints make a long cavity measurement impractical, and for measuring large astronomical and aerospace telescope optics.

A Twyman-Green interferometer can be used in an autocollimation setup to easily measure small- to large-diameter optics.

Verifying Surface Quality in Autocollimation

parabola in autocollimation, optical setup

Typical setup for measuring surface quality in autocollimation.

Required Equipment

The diagram below shows the equipment needed to measure a flat of a diameter equal to or smaller than the aperture of the interferometer. Standard AccuFiz Fizeau interferometers are available in either 100mm or 150 mm apertures.

Want a convenient reference to this and other optical test setups? Download the Common Optical Testing Setups guide (PDF).

Download the Optical setups guide

Required Components
Twyman-Green Interferometer	More Information
Diverging Optic	Specifications
5-Axis Stand	Specifications
Dovetail Mount	Specifications
Bayonet, 3-Jaw, or Shelf Mount	Specifications
2-Axis Base with Tip/Tilt	Specifications

Measuring in Vibration

With a traditional, phase-shifting interferometer, measurement data is acquired sequentially—a long enough process that vibration and air turbulence will degrade or even prevent measurement. The interferometer and all mounts must be situated on an air table to isolate the system from vibration. Air isolation can be expensive—prohibitively expensive for very large optics or long measurement paths.

4D PhaseCam Twyman-Green interferometers include Dynamic Interferometry^®, which enables all measurement data to be acquired simultaneously. Vibration is no longer an issue, and an isolation is not needed— a huge cost savings for very large optics or long measurement paths.

What is a Twyman-Green interferometer?