The MTF benches of OEG provide fully automatic characterization of imaging quality on- and off-axis for any azimuth and type of object/image conjugates by measurement of the modulation transfer function (MTF).

 

The operational area covers almost all standard optics for the visible and NIR spectral range.

 

The modulation transfer function (MTF) is a recognized control criterion for the optical imaging quality. It characterizes the resolution of optical systems on the axis and in the image field. Beside the MTF a lot of other parameters can be measured, e.g. the focal length, chromatic aberrations, distortion, astigmatism, field curvature, depth of field.

 

Already since 1991 OEG GmbH works in the field of MTF measurement.

 

The OEG-MTF-benches are working satisfactorily with many german and international considerable optics manufacturers in the production control. In addition it is also outstanding suitable for the employment in teachings, research, laboratory as well as goods in and outgoing inspection.

 

 

 

 

Despite the presence of sophisticated design and manufacturing techniques, lenses can still vary considerably in imaging quality because of manufacturing errors. Because of the growing demands in imaging performance of lenses their characterisation by help of the Modulation Transfer Function (MTF) as the premier parameter for objectively evaluating is more and more used.

The optical industry uses this parameter as meaningful quality function for the objective evaluation of optical systems.

The MTF describes how the image contrast varies with spatial frequencies. It is expressed as the ratio of contrast in the image to contrast in the object as a function of spatial frequency of a line grid with cosinus functional transmission. Spatial frequency is expressed in terms of line-pairs per millimeter (lp/mm). The MTF combines image resolution and contrast into a common representation.

Another feature of an MTF measuring instrument is, that it allows system testing in situations similar to actual applications. Field angle positions, spectral ranges, distances between object- and image plane can be replicated or simulated in the test of an optical system.

The MTF measurement is based on the evaluation of the test chart image, provided by the lens under test. As test chart an edge or a gap (haircross) is used.

The test chart image is seized with highest accuracy and evaluated by an image processing system using the according mathematical algorithms.

The fourier transformation of of the line spread function results to the complex optical transfer function. The MTF is the magnitude of the fourier transformation of the line spread function.

 

 

The measurement can be performed interactive or in the automatic mode.

The automatic mode is used for the serial test of specimen of the same type.

The interactive mode is used for the evaluation of special specimen.

In the interactive mode the MTF is shown in real time on the PC screen.

The results of interactive measurements can be stored and represented together with diagrams in measuring protocols.

 

In the fully automatic measuring mode, measuring templates are processed automatically. Measuring templates can be generated freely by the operator.

 

After the start the complete measurement runs off fully automatic.

real time calculation and representation of MTF, ESF (edge spread function) and LSF (line spread function)

fast switching between tangential and sagital MTF measurement

comparison with freely selectable desired MTF-values in the diagram

real time MTF for fine tuning during the objective assembly

simple change between different measuring wavelengths

fast change between measurement on the axis and in the image field

alternatively manual or automatic azimuth-dependent measurement

automatic symmetry measurement

operation and controlling of the hardware by Joystick, mouse and PC keyboard

automatic production of meaningful metrology records (quick report)

diagram of the focus curve (contrast for given spatial frequency)

software controlled or manual focusing

automatic focusing with a user selected spatial frequency

manual or automatic measurement of chromatic aberrations

measuring procedure very easily programmable by user

measurement of focal length (infinite / finite) or magnification (finite / finite)