Modulation transfer function

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 offaxis angles for characterizing the MTF at the corresponding image fields.

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 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.

Modern MTF- Testers like the ImageMaster® use a single illuminated slit on an 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 Line Spread Function (LSF).

One new technology in the mobile phone market is under-display camera technology – camera optics are almost invisibly hidden under full-screen display surfaces.

Light Diffraction is a complex topic, but at Rainbow Symphony, we take great pride in being a gateway to the joys of science for learners at all levels. We’ll take you step-by-step through the basics and show you how you can do your own fun experiments and learn the science of diffraction.

Another great example of light diffraction in nature are the rings of light (corona) observed around the sun and other celestial bodies. This is caused by light wave diffraction by small particles in the atmosphere. Even the sky’s apparent blue color, is an example of light diffraction at work. When sunlight hits the earth’s atmosphere, colors of longer wavelengths simply pass through. However, blue, which has a relatively short wavelength, diffracts and scatters upon collision with the atmosphere’s molecules.

Light waves are known to behave in one of three ways when they reach the boundary of a medium. That is, the end of one medium and/or the beginning of another. They are either reflected, refracted, or diffracted.

Just as Huygen’s principle states, when a light wave comes in contact with a diffraction grating, the light disperses, forming many point sources with their centers at each slit. Constructive and destructive interference between the ‘new’ light waves occur where their valleys and peaks meet or oppose each other, respectively.

Come see TRIOPTICS consultant Daniel Winters present: Metrology and alignment solutions applied for pancake lenses used in VR systems

The MTF is a tool for optical designers to quantify the overall imaging performance of a system in terms of resolution and contrast. Knowledge of the MTF curves of the lenses and camera sensors involved in an optical system is used for optimization of the optical system performance.

Explore the selection of fun products at the Rainbow Symphony store to continue your exploration of light diffraction, including our diffraction glasses and rainbow suncatchers. We also carry three types of diffraction grating slides: the double axis 13,500 line/in diffraction grating slide, the linear 1000 line/mm diffraction grating slide, and the linear 500 line/mm diffraction grating slide.

TRIOPTICS offers a broad product portfolio in the field of MTF measurement. This also includes model variants for measurement requirements that result from the latest technology trends for smartphone camera optics.

You can observe light’s color spectrum by viewing a light source through a diffraction grating in a dark room. A diffraction grating is used to separate light into its constituent colors. It is an arrangement of a large number of equidistant parallel narrow scratches of equal width which are separated by equal opaque sections.

MTFimage quality

All electromagnetic waves are light, but only light from a certain section of the electromagnetic spectrum is visible to the human eye. Electromagnetic radiation with a wavelength between 380 nm and 760 nm is visible to the human eye. This range is referred to as the visible light spectrum. On the electromagnetic spectrum, the visible light spectrum falls between infrared and ultraviolet waves. The visible effects of diffraction are most pronounced when the length of the opening through which the wave is passing is close to the light’s wavelength.

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.

The modulation transfer function varies in relation to the spatial frequency and 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.

With its ImageMaster® product range, TRIOPTICS is the market leader for MTF (modulation transfer function) measurement equipment for high-precision determination of image quality. The ImageMaster® series has been specially developed for measuring the MTF to enable the precise determination of the imaging quality of lenses and optical systems. For this purpose, in addition to the MTF as the generally accepted method for determining the imaging quality of a lens, a variety of other optical parameters are measured.

Mtf cameranikon

Let’s start with Huygen’s Principle. Christiaan Huygens was a brilliant Dutch physicist, mathematician, inventor, and astronomer, known especially for his contributions to optics and mechanics. The explanations for all three phenomena of light wave behavior are rooted in Huygen’s principle, which states that every point on a wavefront is a source of wavelets, which spread forward at the same speed.

High-resolution, professional photography and the zoom capability of cameras are two further key drivers for the future. All three trends cause new challenges for measurement technology, for which TRIOPTICS is introducing customized measurement solutions for image quality testing.

Constructive interference occurs in different directions for different colors due to the differing wavelengths of the colors that make up the visible spectrum. Based on this, we can point a diffraction grating at a white light source and view the different colors in the spectrum.

MTFchart

This article inspired you? Are you looking for further knowledge transfer? Then you might also be interested in the following topics …

With the three new developments of the ImageMaster® PRO series TRIOPTICS underlines its technology leadership also for the production of future mobile phone camera lenses.

Examples of light diffraction can be seen in nature every day! Take, for instance, a cloud’s ‘silver lining’. This visual effect is a result of sunlight bending around the edge of the cloud. The various colors sometimes observed in clouds is another example of light being diffracted, this time by the clouds water droplets. This is called cloud iridescence and is most often observed in cirrocumulus, altocumulus, lenticular, and cirrus clouds. The different colors illustrate how waves of different wavelengths are diffracted differently and ‘scattered’.

We offer a comprehensive product range for software-supported fully automatic measurement of the modulation transfer function (MTF) for both R&D and production or optics manufacturing.

MTFOptics

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).

MTF is used for a wide range of optics from simple components such as spherical single lenses to complex lenses. Examples include photolithographic optics, intraocular lenses, endoscopes, riflescopes, telescopes, spotting scopes, binoculars, AR/VR optics, cine lenses, automotive lenses and many others.

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 with the design data. Manufacturing errors, assembly and alignment errors in the optics will deteriorate the overall imaging performance of the system.

Contact our team at Rainbow Symphony today for help adding splashes of color to your life and turning experiences from ordinary to extraordinary. Also, keep checking our blog for stimulating discussions on all things relating to light and color.

Mtf cameraexplained

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 also 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. Manufacturers can compare the image quality of the manufactured lenses with the design expectations.

MTFlens

The modulation transfer function (MTF) is the generally accepted and fundamental parameter for the characterization of optical systems worldwide. MTF is a quantitative measure as well as an objective criterion for the imaging quality of optics.

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 the limit of resolution for a given optical system or what is known as the cut off frequency (see figure below). When the contrast value reaches zero, the image becomes a uniform shade of grey.

MTF cameratest

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 the 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 the tangential azimuth.

These phenomena are not unique to visible light waves. In fact, they can be observed for any wave, including sound waves, water waves, or any wave in the electromagnetic spectrum. However, this blog will focus on the wonders of diffraction of visible light waves.

The contribution of each spatial frequency to the LSF can be calculated on the basis of the Fourier analysis. Actually, the amplitude of each spatial frequency is equal to the contrast at this frequency. The Fourier analysis of the Line Spread Function corresponds to the MTF of the sample. Taking a single image of the LSF unveils the complete MTF.

Lenses can vary in their imaging quality during production. To meet the often high demands on imaging performance, lenses are characterized and evaluated using MTF as the most important parameter. MTF provides a meaningful quality function for the objective evaluation of optical systems in the optical industry. When it comes to imaging an object with the desired accuracy, MTF data provide the necessary basis for optical design. Resolution and contrast are of particular importance. MTF data can greatly simplify the selection of the appropriate lens for an application.

For years, the ImageMaster® PRO product family has set the global standard for testing the imaging quality of mobile phone camera lenses in mass production.

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 the 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.