ImageMaster^® HR

Fully or semi automated, ultra-accurate, multi functional MTF-Test Station

ImageMaster^® HR is a fully equipped though compact R&D quality MTF test station for medium sized sample lenses. Its design is kept modular and upgradeable allowing for almost unlimited optical test applications today or in future. The instrument is used in the R&D laboratory as well as in the quality control or in production. The unique vertical setup of ImageMaster^® HR is space saving in the measurement room and ensures the most convenient and accurate positioning of the sample lens mounts. For the majority of lenses this vertical measurement with the gravitational force along the optical axis is advantageous. This way the lens can be kept in the sample holder in a precise and stable position supported by its own weight.

For the object generator a high quality refractive collimator is mounted above the sample table on a motorized pivoting arm equipped with a backlash free transmission gear. The collimator projects the MTF test target to the entrance pupil of the sample.

Optimal design prevents vignetting

To prevent vignetting the location of the entrance pupil can be precisely adjusted to the collimator's center of rotation depending on the sample height. This unique feature is ensured by the precise height adjustment of the complete sample holder assembly into the appropriate position.

Largest off-axis angles for ultra-wide field angles

A precision swinging arm for the object generator equipped with a backlash free rotation gear allows for ultra-wide field angles of +/-120°. The standard high accuracy of the angular positioning provided by the stepper motor can be further increased by a high precision angular encoder. TRIOPTICS is using only high quality Heidenhain encoders providing excellent absolute accuracy and resolution of 0.18 arcsec. For accurate distortion measurements of lenses with short focal length the use of the angular encoder is a prerequisite.

Motorized finite conjugates stage for long conjugate distances

An additional linear stage with a target generator consisting of a reticle changer and illumination unit is optionally available for the finite-finite imaging configuration. For operator convenience the distance setting of the conjugate distances is motorized. The distance setting for a certain sample can be saved to a file and used for future measurements.

The finite conjugates assembly features both long conjugate distances (up to 1 m) and very large object height (standard +/-500 mm, as special version up to +/-1 m).

High quality image analyzer

The centerpiece of ImageMaster^® HR is the high-quality image analyzer including relay optics of negligible residual aberrations, selected and tested CCD camera and perfectly aligned optical head assemblies.

The high-quality image analyzer with an exchangeable high-NA microscope relay lens is located beneath the sample table. It is mounted on precision motorized linear stages for focus and image field positioning. For the ultra precise distortion and EFL measurement the object generator arm and the image field stage can be optionally equipped with precision encoders assuring the accurate position feedback needed in these measurements.

Precision Sample holder

The measurement accuracy of a MTF-Test Station is significantly influenced by the quality and stability of the sample holder. The sample holder integrated in ImageMaster^® HR includes an ultra accurate rotary bearing, precision reference surfaces square and parallel to the optical axis, rotation facilities over 360° and fine adjustment in X, Y direction. The rotation of the sample holder is alternatively available in manual or software controlled motorized version.

State of the art software

The most comprehensive software on the market extends the measurement capabilities and allows for the complete characterization of optical systems:

• MTF on-axis and off-axis
• Though Focus characteristics
• EFL
• FFL
• Distortion
• Astigmatism
• Field curvature
• Chromatic aberrations
• Chief ray angle
• F/#
• Vignetting
• Field of View
• Relative illumination etc.

The state of the art software features advanced capabilities for the detailed analysis of all aspects in imaging quality evaluation. The high resolution (0.01 MTF) and accuracy (0.02 MTF) of ImageMaster^® HR is individually verified and certified for each instrument using PTB certified samples. The measurement results are thus directly traceable to national and international standards.

Simultaneous MTF measurement in the sagittal and tangential planes with a crosshair target

Features and Measurement Configurations

• Vertical set up
• Automated angle setting for off axis measurements with collimator on pivoting arm and motorized by a stepper motor
• Autofocus function using stepper motor stage
• Automated field position stage using a stepper motor stage
• Measurement in the CCD spectral range
• Optional finite-finite imaging stage available
• Optional encoder set for precision distortion and EFL measurements available
• Exchangeable high-NA relay lenses
• Broad range of collimator focal lengths from 25 mm up to 500 mm available to adapt to the sample EFL.
• Filter changer for quick measurement wavelength selection and chromatic aberration measurements.
• Software includes a script language for user defined measurement procedures and Microsoft Excel export.
• Classical and reverse imaging configuration possible

Classical Configuration

In this test configuration the collimator on the pivoting arm projects the test target towards the entrance pupil of the sample. The sample is imaging the target to its focal plane. This image of the test target is magnified by the microscope relay lens and projected onto a CCD sensor. The instrument can be configured for testing optical systems with:

• object at infinity using the collimator on the pivoting arm
• object and image at finite conjugates using the finite object stage with illuminated target reticle

Reverse Imaging Configuration

In this configuration the illuminated target reticle is placed in the image plane of the sample lens. The parallel beam emerging from the sample's entrance pupil is collected by a precision telescope and focussed onto the CCD.

For certain sample types and test conditions this is a very economic solution for saving the expensive relay lens. Furthermore, the target reticle can be designed and precisely manufactured with test patterns at fixed image field positions to be tested, thus saving the field stage, too. Both is possible without sacrificing the measurement accuracy. This makes this configuration the preferred solution for production testing where the somewhat limited flexibility is acceptable. TRIOPTICS was the first company to introduce this MTF measurement method to high volume MTF production test equipment (refer to ImageMaster^® PRO series).

Two possible configurations are possible:

• image at infinity using the telescope on the pivoting arm and the test object in the focal plane
• object and image at finite conjugates using the test object at the shorter conjugate and a linear stage with CCD camera at the longer conjugate