Product Overview
Software
Technical Data
Upgrades & Accessories
Knowledge Base
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ImageMaster HR IR brochure
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ImageMaster HR brochure – Options and Upgrades
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ImageMaster® HR/Universal

Image quality testing for small and large lenses

The devices ImageMaster® HR and Universal provide an outstanding level of accuracy and flexibility when testing the MTF (modulation transfer function). The equipment is modular and upgradeable to allow for custom configuration as test requirements change. The instrument can be configured for testing optical systems with the object at infinity or object and image at finite conjugates. The accuracy of the measurement is traceable to international standards.

The ImageMaster® HR offers versatile functionality for testing the image quality of small and medium-sized lenses, e.g. for smartphone, photo and film cameras. For medium and larger lenses, e.g. in camera lens manufacturing and the development of aerial lenses or lenses for space exploration, the horizontally mounted ImageMaster® Universal offers the highest accuracy and maximum stability.

Product Overview ImageMaster® HR

ImageMaster® HR UltraPrecision

Ultra-precise image quality testing
ImageMaster® HR UltraPrecision

For ultra-precise measurement of MTF and other optical parameters TRIOPTICS has developed the top model among the MTF test stations of our HR product series – the ImageMaster® HR UP.

  • High-precision air bearing sample holder

  • Increased mechanical stability

  • Enhanced measurement reproducibility

  • Accuracy traceable to international standards
  • Fully or semi-automated, ultra-accurate, multifunctional MTF test station
  • R&D MTF test station for medium sized samples
  • MTF measurement at finite and infinite conjugates
  • Instrument available for NUV / VIS / NIR
  • Vertical set up for most convenient and easy lens positioning
  • Optimal design prevents vignetting

ImageMaster® HR

The preferred MTF test station worldwide
ImageMaster® HR

The ImageMaster® HR fulfils the high customer requirements for accuracy and flexibility in the measurement of image quality.

  • Fully or semi-automated, ultra-accurate, multi-functional MTF test station

  • Accuracy traceable to international standards

  • MTF measurement at finite and infinite conjugates

  • For small and medium sized samples
  • Available for NUV/VIS/NIR/LWIR spectrum
  • Vertical set up for most convenient and accurate lens positioning
  • Ultra-wide field angle of ± 110°
  • Optimal design prevents vignetting

ImageMaster® HR MAX

Testing with mirror collimators
ImageMaster® HR MAX

ImageMaster® HR MAX has been developed for high-precision MTF testing in the VIS and IR range.

  • Available for NUV/VIS/NIR spectrum

  • Includes a high-quality mirror collimator, halogen light source and high resolution camera sensor

  • Accuracy traceable to international standards

  • Fully or semi-automated, ultra-accurate, multi-functional MTF test station
  • For medium sized samples
  • MTF measurement at finite and infinite conjugates
  • Vertical set up for most convenient and easy lens positioning
  • Ultra-wide field angle of ± 70°
  • Optimal design prevents vignetting

ImageMaster® HR MAX IR

High End MTF testing in the IR range
ImageMaster® HR MAX IR

The ImageMaster® HR MAX IR is designed for the measurement of MTF and other optical parameters of today’s high-end IR optics in R&D and production.

  • Available for NUV/VIS/NIR/MWIR/LWIR spectrum (SWIR on request)

  • Includes a high-quality mirror collimator, broadband IR light source and IR focal plane array image sensor

  • Accuracy traceable to international standards

  • For small and medium sized samples
  • MTF measurement at finite and infinite conjugates
  • Time-saving area sensor method for LWIR and MWIR
  • Vertical set up for most convenient and easy lens positioning
  • Ultra-wide field angle of ± 70°
  • Optimal design prevents vignetting

Product Overview ImageMaster® Universal

ImageMaster® Universal

Horizontal MTF measurement in a wide spectral range
ImageMaster® Universal

Innovative design, high quality and long-life components are combined in the ImageMaster® Universal with user-friendly software. Its horizontal construction facilitates testing of large lenses.

  • Accurate measurement of virtually any existing lens system: infinite, finite, afocal

  • For high performance photographic imaging lenses up to high resolution telescopes

  • Spectral range of the MTF measurement from UV to visible spectrum to IR (NIR/SWIR/MWIR/LWIR)

  • On-axis and off-axis-measurement of the MTF
  • Modular and upgradable design
  • Module exchange within a few minutes (e.g. changing from VIS to IR)
  • MTF values traceable to international standards
  • Cover for collimators protects from ambient light and air turbulences

ImageMaster® Universal 3D

Full field MTF measurement system for infinite and finite object distances
ImageMaster® Universal

The ImageMaster® Universal 3D enables the full field measurement without rotating the sample under test. The sample remains in a fixed horizontal position while the automated target generator and the image analyzer scan the complete target respectively image plane.

  • Full field measurement for infinite and finite measurement situations

  • Measurement of the modulation transfer function (MTF) off-axis and on axis

  • MTF values based on international standards

  • Fully automated, ultra-accurate, multi-functional MTF- Test Station

  • Optimal design prevents reduction of the image brightness
  • Motorized finite conjugates stage for long conjugate distances
  • High quality image analyzer
  • Collimator rotates around two axes to cover an object angle of ±60° over the full field azimuth
  • The reticle including illumination unit cover a rectangular object field of ±1100mm (horizontal) and ±800mm (vertical)
Request ImageMaster® R&D
ImageMaster® HR Anwendung

Applications

ImageMaster® HR

The ImageMaster® HR MTF test station measures visual and infrared lenses:

  • MTF on-axis and off-axis
  • Effective Focal Length (EFL

  • Distortion

  • Field curvature

  • Lateral and longitudinal chromatic aberrations

  • Astigmatism

  • Chief Ray Angle

  • PSF (Point Spread Function)

  • Veiling Glare

  • Depth of focus

  • Field of view

  • Flange Focal Length (FFL) relative

  • Relative transmission

  • Relative illumination

All MTF measurements can be performed with the ImageMaster® HR in finite and infinite measurement position.

ImageMaster® Universal / Universal 3D

With the MTF test station ImageMaster® Universal lenses can be measured in all spectral ranges from UV to LWIR.

The ImageMaster® Universal 3D enables MTF measurements in the visible spectral range (VIS):

  • MTF on-axis and off-axis
  • Effective Focal Length (EFL

  • Distortion

  • Field curvature

  • Lateral and longitudinal chromatic aberrations

  • Astigmatism

  • Chief Ray Angle

  • PSF (Point Spread Function)

  • Depth of focus

  • Field of view

  • Back focal length (absolute/relative)

  • Relative transmission

  • Relative illumination

All MTF measurements can be performed with the ImageMaster® Universal in finite, infinite and afocal measurement position.

The ImageMaster® Universal 3d enables measurements in finite and infinite measurement position.

Software

ImageMaster® MTF Lab Software

User-friendly software for research and development as well as laboratory work.

The versatile functionality and high performance make the user-friendly ImageMaster® MTF-Lab software package the preferred choice for R&D and laboratory work. High-performance functions help the user to optimize the measurement processes.

The software offers high flexibility for measurements in the NUV-, VIS- and NIR spectrum. Automatic measurement sequences ensure easy operation and the data can be output in CSV/MHT.

Several useful functions are integrated which help the user to scan and perceive the correct image position of the sample under test. Changing the measurement mode is easy and time-saving. All important measurements for the imaging properties are quickly accessible.

One main feature key feature when using the software with the ImageMaster® Universal is the support of UV or IR detectors employing the scanning aperture method.

  • Easy to handle graphical user interface makes the most important functions only one mouse-click away
  • Customizable arrangement of graph windows
  • Measurements of MTF, EFL and a range of other parameters using special target patterns and dedicated software routines
  • Functions for easy alignment of the sample under test
  • Conventional MTF measurement using a single slit or a crosshair as a target
  • Optionally automated selection and positioning of the suitable reticle (target) and filter for the current application
  • Configuration files with optimized process parameters and password protected access for operator and supervisor
  • Script tools for custom programming and analysis
  • Intuitive user interface and time-saving lens test routines
  • Logging of successive measurements
  • Data export to a variety of file formats
  • The certificate in HTML format can be imported into MS Excel

Technical Data

ParameterImageMaster® HR VISImageMaster® HR IRImageMaster® HR MAXImageMaster®® HR MAX IRImageMaster® HR UltraPrecision
Optical set upInfinite conjugates
(finite optional)
Infinite conjugatesInfinite conjugates
(finite optional)
Infinite conjugates
Max. off-axis angleUp to ±110°Up to ±110°Up to ±70°Up to ±70°
Spectral range450 nm … 750 nm, halogen (NIR/NUV optional)LWIR: 8 µm … 12 µmVIS /NIR
NUV optional
NIR, NUV, LWIR: 8 µm … 12 µm
VIS: 0.4 µm … 0.9 µm
MWIR : 3 µm … 5 µm
SWIR: 0.9 µm … 1.7 µm on request
Azimuth range360°360°360°360°360°
Max. image height±23 mm±23 mm±23 mm±23 mm±23 mm
Clear apertureup to 100 mmup to 100 mmup to 100 mm
Collimator range50 mm … 500 mm50 mm2)50 mm … 1,000 mm50 mm … 1,000mm2)50 mm … 1,000 mm
EFL range of the sample1 mm … 150 mm 1)1 mm ... 10 mm1),2)1 mm … 200 mm 1)1 mm … 200 mm 1)1 mm … 200 mm 1)
Spatial frequency
(in specification)
Max. spatial frequency
0 lp/mm … 500 lp/mm
1,000 lp/mm
(depending on sample)
0 lp/mm … 60 lp/mm0 lp/mm … 500 lp/mm
1,000 lp/mm
(depending on sample)
VIS/NIR/LWIR: 0 lp/mm … 60 lp/mm
MWIR: 0 lp/mm … 100 lp/mm
0 lp/mm … 500 lp/mm
1,000 lp/mm
(depending on sample)
Accuracy
(MTF on-axis and off-axis)
±0.02 MTF±0.03 MTF±0.02 MTF±0.03 MTF±0.02 MTF
Repeatability
(MTF on-axis and off-axis)
±0.005 MTF±0.02 MTF±0.005 MTF±0.02 MTF±0.005 MTF

1) Depends on mirror collimator
2) Larger on request

Download Technical Data

ImageMaster® R&D Universal

ParameterImageMaster® Universal
Optical set upFinite, infinite or afocal
Max. off-axis angle±180
Spectral rangeUV: 250 nm … 450 nm
VIS: 450 nm … 700 nm
NIR: 700 nm … 1.000 nm
SWIR: 1.000 nm … 2500 nm
MWIR: 3 µm … 5 µm
LWIR: 7 µm … 13 µm
Azimuth range360°
Max. image height±50 mm
Spatial frequency
(in specification)
Max. spatial frequency
UV: 100 lp/mm
VIS / NIR: 500 lp/mm
SWIR: 120 lp/mm
MWIR: 80 lp/mm
LWIR: 60 lp/mm
Accuracy
(MTF on-axis and off-axis)
±0.02 MTF on axis
±0.03 MTF off axis
Repeatability
(MTF on-axis and off-axis)
±0.01 MTF
EFL (Effective Focal Length)
Accuracy
±0.2 %
Distortion
Accuracy (without / with encoder)
Repeatability (without / with encoder)
±0.7 % / ±0.25 %
±0.3 % / ±0.1 %
Lateral chromatic aberration
Accuracy
Repeatability
±0.5 µm
±0.3 µm
Longitudinal chromatic aberration
Accuracy
Repeatability
±1 µm
0.2 µm
CRA
Accuracy
Repeatability
±1°
±0.4°
FFL (relative)
Accuracy
Repeatability
±2 µm
±1 µm
Astigmatism
Accuracy
Repeatability
±4 µm
±1 µm
Field curvature
Accuracy
Repeatability
±2 µm
±1 µm
Download Technical Data
Request ImageMaster® R&D

Upgrades & Accessories

ImageMaster® HR

The ImageMaster® HR is adapted to customer-specific measurement requirements by means of versatile upgrades.

  • Motorized ultraprecise sample holder with a radial runout better than 3 μm / 6 arcsec for more accurate measurements of tilt sensitive samples
  • Additional filters and reticles for all measurement applications: Filters for NUV, VIS, NIR / reticles extendable, e.g. for PSF and veiling glare measurements
  • Extensions of nearly all stages to suit the customer’s needs

• Motorized finite conjugate stage with manual or motorized object generator. The motorized object generator illuminates the reticle in the direction of the sample
for off-axis measurements. This is needed for small samples or low light conditions
• Various collimators with focal length and clear aperture for high flexibility
• Motorized reticle and filter changer for infinite conjugate to measure with least interaction of an operator. The lateral chromatic aberration can be measured more accurately as the filter will be changed automatically with no vibration of a manual change
• With the veiling glare upgrade for ImageMaster® HR it is possible to measure the Glare Spread Function (GSF). By off-axis measurements and rotation of the specimen around its center, the GSF can be measured over the entire field of view of the sample.

ImageMasterHR_VIS

Upgrade ImageMaster® HR to CamTest R&D

TRIOPTICS provides customers maximum versatility offering a combined test system. The three exchangeable measurement heads offer the following possibilities:

ImageMaster® HR
Image quality measurement of lenses with following parameter:

  • MTF on-axis and off-axis
  • Effective Focal Length (EFL)
  • Distortion
  • Field curvature
  • Lateral and longitudinal chromatic aberrations
  • Astigmatism
  • Chief Ray Angle
  • PSF (Point Spread Function)
  • Veiling Glare
  • Depth of focus
  • Field of view
  • Flange Focal Length (FFL) relative
  • Relative transmission
  • Relative illumination

ProCam® Test R&D
Image quality measurement of camera modules with following parameter:

  • Line Spread Function (LSF)
  • MTF
  • Distortion
  • Effective Focal Length (EFL)
  • Shift, tilt and defocus of the sensor
  • Image field curvature of the lens
  • Lateral and longitudinal chromatic aberrations

ImageMaster® Universal

Enhance the functionality of your ImageMaster® Universal system with comprehensive upgrades and accessories.

Light sources for different wavelengths are available for the ImageMaster® Universal:

  • UV
  • VIS / NIR / SWIR
  • MWIR/LWIR
ImageMaster® Universal Light sources

MWIR/LWIR Light Source for ImageMaster® Universal

Various camera based or scanning based detectors are available as image analyser for different wavelength ranges:

  • UV (scanning based)
  • VIS (camera/scanning based)
  • NIR (camera/scanning based)
  • SWIR (scanning based)
  • MWIR (kamera-/scannerbasiert)
  • LWIR (kamera-/scannerbasiert)
Camera VIS for ImageMaster® Universal

Camera VIS for ImageMaster® Universal

Upgrades_Holder_Adjustable_Holder

Detector MWIR for ImageMaster® Universal

Sample Holders for various diameters and a lifting table for large samples are available for the Image Master® Universal.

ImageMaster® Universal Upgrades & Accessories

Sample Holder for ImageMaster® Universal

Upgrades_Holder_Adjustable_Holder

Lifting table for ImageMaster® Universal

For finite conjugate measurements a finite stage is available as upgrade in two different stage lengths for all wavelength ranges:

  • Finite Stage 2m
  • Finite Stage 3m
ImageMasterUniversal_Finite-Stage

Finite Stage for ImageMaster® Universal

For different measurement requirements various reticles and filters are available. With the motorized reticle and filter changer they are changed easily and within short time.

  • Reticle and filter changer
  • Reticles
  • Filter
ImageMaster® Universal Upgrades & Accessories Reticles and Filters

Reticle and Filter Changer

Upgrades_Holder_Adjustable_Holder

Reticles

Upgrades_Holder_ClampFixture

Filters

The automated ultra-precision afocal unit is available as upgrade for afocal samples. With different autocollimator lenses for the afocal unit measurement in different wavelength ranges can be executed.

Afocal unit with

  • Decollimator lens for VIS
  • Decollimator lens for MWIR
  • Decollimator lens for LWIR

ImageMasterUniversal_Afokaleinheit

Afocal unit

Knowledge Base

MTF and image quality

MTF Testing / Measurement / Inspection – Modulation Transfer Function

The Modulation Transfer Function (MTF) is an important aid to objective evaluation of the image-forming capability of optical systems. Not only that the MTF provides a means of expressing the imaging quality of optical systems objectively and quantitatively, but it can be calculated from the lens design data. In this way it allows optical and systems designers to predict reliably the performance of the optical systems. The manufacturers can compare the image quality of the manufactured lenses with the design expectations.

The MTF measurement is an important tool for the objective assessment of the imaging performance of optical systems. Moreover, the MTF can be calculated from the lens design data giving designers of optical systems the ability to predict system performance reliably. The manufacturer can then compare the image quality of real lenses with the expectations from the design phase.

MTF-Modulation Transfer Function

The Modulation Transfer Function (MTF), describing the resolution and performance of an optical system, is the ratio of relative image contrast divided by relative object contrast MTF = Relative Image Contrast/Relative Object Contrast. When an object (illuminated target or reticle) is observed with an optical system, the resulting image will be somewhat degraded due to inevitable aberrations and diffraction phenomena. In addition, a real lens will not fully conform to the design data.

More knowledge for experts

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ImageMaster R&D KnowledgeBase

Perfect grid pattern is imaged through the sample into the image plane

ImageMaster R&D KnowledgeBase

Contrast vs spatial frequency. This figure shows the MTF of the diffraction limited optics and a measured MTF referring to Fig. 1

TRIOPTICS ImageMaster R&D KnowledgeBase

The image of a perfect slit is called “Line Spread Function”

Manufacturing errors, assembly and alignment errors in the optics will deteriorate the overall imaging performance of the system. As a result, in the image, bright highlights will not appear as bright as they do in the object, and dark or shadowed areas will not be as black as those observed in the original patterns. In general an illuminated target can be defined by its spatial frequency (number of bright and dark areas per millimeter) and the contrast (the apparent difference in brightness between bright and dark areas of the image).

By convention, the modulation transfer function is normalized to unity at zero spatial frequency. For low spatial frequencies, the modulation transfer function is close to 1 (or 100%) and generally falls as the spatial frequency increases until it reaches zero. The contrast values are lower for higher spatial frequencies as shown above. As spatial frequency increases, the MTF curve falls until it reaches zero. This is limit of resolution for a given optical system or the so called cut off frequency (see figure below). When the contrast value reaches zero, the image becomes a uniform shade of grey.

ImageMaster R&D KnowledgeBase

Typical setup for off-axis MTF measurements.

The grids shown are actually no longer used in order to measure the MTF. Modern MTF-Testers like the ImageMaster® use a single illuminated slit on opaque background as the object. From a mathematical point of view a single slit can be regarded as the sum over all spatial frequencies (Fourier synthesis). All frequencies contribute with the same amplitude (=1) to this slit not taking the finite slit width into account for this description. This single slit will be imaged into the image plane of the sample. Due to diffraction and aberrations there will be no perfect slit image in this plane, instead the slit image is broadened. It represents the so called Line Spread Function (LSF). On the basis of Fourier analysis the contribution of each spatial frequency to the LSF can be calculated. Actually the amplitude of each spatial frequency is equal to the contrast at this frequency. The Fourier analysis of the Lines Spread Function corresponds to the MTF of the sample. Taking a single image of the LSF unveils the complete MTF. Alternatively it is also possible to use a cross (i.e. two perpendicular slits) for the target. This enables the ImageMaster® to measure the MTF in two image directions simultaneously provided a CCD camera is used for the image analyzer. And finally a pinhole target can be used as the object, too. The image of a pinhole target is called Point Spread Function. This function contains the complete MTF information in all image directions. The basic terms and mathematical relations used for MTF are described in the ISO 9334 standard.

The modulation transfer function varies not only related to the spatial frequency but also with the position in the field of view. The MTF measurement along the axis of symmetry of the optical system is known as on-axis measurement.

To completely characterize the imaging performance of an optical system, the MTF must be measured at different positions within the field of view. The MTF measurement within the field of view is known as off-axis measurement. In order to achieve an off-axis measurement, the target is moved in the field of view at the desired object position and the image analyzer to the corresponding image position.

The MTF measurement can be accomplished at a single wavelength or in a spectral range covering a finite band of wavelengths. The resulting measurement data are known as monochromatic or polychromatic MTF values, respectively.

Usually the MTF is used in its one-dimensional form, calculated for one azimuthal section through the image plane. The azimuth (section plane) of the object pattern is called sagittal azimuth when the prolongation of the slit or object passes through the reference axis. When the prolongation of the slit pattern is perpendicular to the reference axis, the azimuth is called tangential azimuth.

In this so-called finite-finite imaging condition the illuminated slit or crosshair target is directly moved in the object plane of the sample. In the more common infinite-finite imaging condition, the illuminated slit or crosshair is part of a collimator projecting the target to infinity. The collimator is then oriented at different off axis angles for characterizing the MTF at the corresponding image fields. Figure 4 shows the typical setup for this imaging condition.

ImageMaster R&D KnowledgeBase

Typical setup for off-axis MTF measurements.

EFL

The Effective Focal Length (EFL) or equivalent focal length is the distance from the focal points of the lens to the respective principal planes. The EFL determines the magnification of a lens and hence the image size. Because the principal planes are usually inside the lens at unknown locations, the direct measurement of the EFL is difficult.

However, the EFL can be measured quickly and with sufficient accuracy using the method of measuring the magnification of a double bar target. Certified master lenses from PTB (National German Standard Institute) are available at TRIOPTICS and are used for the calibration of the measurement setup. The measurement data are thus directly traceable to international standards.

EFL and Distortion

Distortion is the percentage of change in magnification between the center of the field of view and off-axis positions in the field of view. In order to determine the distortion a different method of measuring the EFL is used:

  • A MTF measurement on axis (at a selected frequency) is carried out. The paraxial focal plane is determined using the MTF measurement at a frequency of interest. To achieve a high accuracy monochromatic light and MTF curve fitting are used while the aperture of the lens is reduced by a diaphragm.
  • An angular field range and a number of measurement points are selected. The object generator will automatically move to the selected field positions.
  • At each position in field the image height is measured. A table with value pairs image height vs. field angles is provided.
  • The EFL is calculated with the formula
  • h/(tan α ) and drawn into a curve vs field angle. A polynomial fitting of the EFL close to α =0 allows the accurate and independent calculation of the paraxial focal length.
  • The distortion is calculated as the ratio between paraxial and field focal length following the ISO 9039:2008.

This procedure requires a comparatively large number of measurement points with accurately known object angles and field positions. For this reason ImageMaster® instruments with dedicated distortion measurement option feature a high precision angular encoder for the object generator (accuracy 5 arcsec) and a high precision linear encoder for the image field stage (accuracy 0.2 μm). This way, the EFL is calculated as an absolute quantity, not depending on calibration parameters.

Depth of focus

The depth of focus is the extent of the region in front of and behind the image plane in which the image will appear to be sharp.

The depth of focus can be determined using a “through focus scan” of the MTF and setting appropriate tolerances for the drop in MTF. The depth of focus between the set tolerances will be measured and displayed.

A more complex measurement can be done simulating the range of object distances covered by the lens and measuring the MTF at the corresponding image distances.

Field Curvature

Field curvature is an optical aberration in which the focus position changes from the center to the edge of the field of view. The curvature of the image field is a lens aberration that causes a flat object surface to be imaged onto a curved surface rather than a plane.

In the presence of the astigmatism, there are two separate astigmatic focal surfaces in orthogonal directions.

To determine the field curvature a set of through focus measurements at different positions in the field are taken. The MTF maxima and the corresponding positions in field are determined. The values are collected by a software routine and displayed in graphical and tabular form.

 

Relative Illumination

Relative illumination in an optical system is the gradual reduction of the image brightness with increased off-axis angle. This phenomenon results from the fall of, which is approximated by the cos4 or “cosine four law of the illumination falloff. Additionally there is the effect of the apparent limitation of the clear aperture depending on the field angle. Relative illumination is defined as the ratio of the central transmission and the transmission at the edge of the field of view.

The ImageMaster®-Software measures continuously the light intensity of the test pattern in order to avoid saturation. In this way the necessary data is available for determining the relative illumination following ISO 13653:1996.

Chief Ray Angle (CRA)

A chief ray is the ray from an off-axis object point which passes through the center of the aperture stop of an optical system. The chief ray enters the optical system along a line directed towards the midpoint of the entrance pupil, and leaves the system along a line passing through the center of the exit pupil. To measure the angle between the optical axis and the chief ray on the image side the following method is used: The lens under test is illuminated by the collimator at different angles corresponding to the object sided chief ray angles. The detector head is moved to the image field position at which the lens focuses the image. Now the detector head is moved towards the lens in small steps while the software registers the lateral movement of the focused spot. From these lateral movements the CRA is calculated.

ImageMaster R&D KnowledgeBase

Measurement procedure of chief ray angle

F-number

The F-Number of a lens is defined by the ratio between the EFL and the diameter of the entrance pupil. The ImageMaster® series instruments use the ISO-517 method to accomplish the measurement: First the EFL is measured according to the procedure described before. Then the sample is turned around with the entrance pupil facing towards the detector head. The diameter of the entrance pupil is measured by first focusing on the left, then on the right edge of the pupil. The travelling distance of the image field stage represents the diameter of the entrance pupil. By choosing the proper head lens of the detector head even pupils positioned far inside of the system under test can be measured.

Blendenzahl

Measurement procedure of F-number

Chromatic Aberrations

Due to the dispersion of refractive optical systems the image position and also magnification of an optical system depends on the wavelength of the light. The dependence of the axial image position on the wavelength is called Chromatic Focal Shift. The dependence of the magnification on the wavelength is called Lateral Chromatic Aberration. Both aberrations can be measured with the ImageMaster®. The collimator of the ImageMaster® is equipped with different narrow bandwidth color filters. Together with the highly corrected relay optics this enables the system to focus in axial direction to the different image positions for different colors. The image position measurement can be done with submicron accuracy. Measuring the lateral image position for different object angles enables the system to measure the lateral chromatic aberration.

chromatische Felder

Principle of the measurement of the axial chromatic aberrations