Define 'PINION'. See more meanings of 'PINION' with examples.

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.

There is some ability to calibrate a camera (which solves the principal distance) at one focus and execute your photogrammetric project at another focus.  The actual discrepancy that is acceptable depends on your accuracy requirements and how much the focus changes.  Generally a calibration done at 2m/6ft focus distance is acceptable for projects up to infinite focus (again depending on accuracy requirements), but may not be acceptable for a project where the focus distance was 50cm/20in.

The Basics: A large depth of field (DOF) means a greater range of the scene is in focus, as opposed to a shallow depth of field when only part of the scene is ...

When you buy a digital camera you will often see the specification “equivalent 35mm focal length”. What does this mean? Most digital cameras have imaging chips that cover much less area than a standard 35mm film frame. Since 35mm film cameras were the standard for so long in photography, much of the techniques and methods were developed around them. A 35mm film camera has a negative that is about 36mm wide by 24mm high (the “35” comes from the physical width of the film stock that is exactly 35mm wide).  A ‘normal lens’ (has a field of view that appears ‘natural’ to humans) on a 35mm film camera has a focal length of 50mm.

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.

Modulation transfer function

Note: A technical photogrammetry term that you may come across is the “Principal Distance”.  Strictly, the Principal Distance is the distance mentioned above (i.e. distance from imaging plane to the lens optical sensor), and the focal length is the principal distance when the lens is focused at infinity. See below for more information on focus vs focal length. When PhotoModeler lists focal length for a camera, it is actually the Principal Distance that is shown.

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.

In many cases though, the advantages of using focus (i.e. crisp targets and distinct features) with subtle effects on principal distance/focal length, outweigh the advantages of keeping focus and principal distance constant (i.e. potentially causing blur in some photos taken at a different distance).

Focal length is a number that is vital to photography and photogrammetry but often misunderstood. What is focal length?

PhotoModeler is one of the leading tools for photogrammetry (the science of generating measurements and accurate 3d data from photography).

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MTFimage quality

A camera typically has focal length in a range of 10mm to 500mm.  Different types of camera can have different ranges and speciality lenses can extend outside this range as well.  A 10mm focal length would be a very wide lens (capturing a lot of the scene), and 500mm would be a very narrow lens (capturing only a small part of the scene – giving a large magnification like binoculars or a telescope).

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.

Mtf cameranikon

All lenses have a stated or specified focal length value (or range of values for a zoom lens). This printed number is actually its nominal length or the principal distance when the lens is focused at infinity. As you focus on objects that are closer to the camera, the principal distance changes.  So for example, a 50mm lens focused on an object a few feet away might have a principal distance of 55mm lens at that time. The most extreme example of this is with a macro setting (a lens setting that allows you to focus on very close, very small objects, under 5″ in size for example). A lens that has a 50mm nominal focal length (so a 50mm principal distance when focused at infinity) might in fact have a 100mm principal distance when focused at a few inches! This is why it is good with photogrammetry (where precise geometry is needed) to calibrate a camera at the distance you will be working with.

Cameras can have fixed lenses (sometimes called ‘prime’ lenses) which have just one focal length, or zoom lenses which allow the focal length to be varied (for example between 18mm-55mm, or 55mm-200mm). For high accuracy photogrammetric work in PhotoModeler, a fixed (or prime) wide lens (such as a 20mm lens on an APS-C frame camera) is recommended as the primary option, but different applications may require different focal lengths, and cameras with adjustable zoom lenses can still be used to achieve very good results with some extra procedural care over the focal length.

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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.

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Depth of field refers to the range of distance that appears acceptably sharp. It varies depending on camera type, aperture and focusing distance, although print ...

MTFchart

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.

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.

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.

Modern digital cameras can have imaging chips that are as small as 6mm by 4mm; some Smartphone cameras are even smaller, and then up to full 24mm by 35mm size.  A very common size is the APS-C format at 16mm by 24mm. This smaller size affects what is considered to be a ‘normal’ focal length.

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Mtf cameraexplained

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).

A strict technical definition of focal length is difficult without providing a lot of background in lens theory, so we will use a simplification. You can think of focal length as the distance between the imaging plane (e.g. the image chip in a digital camera) and a point where all light rays intersect inside the lens (the ‘optical center’). So a focal length of 20mm means that the distance from the optical center to the imaging plane is 20mm long (about ¾ of an inch). What does the focal length number mean?

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

MTFOptics

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.

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.

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.

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.

Learn how to use PhotoModeler with your camera to create detailed digital models: www.photomodeler.com/products/why.html

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.

MTFlens

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The symbol, f, represents the focal length. F/ number is a measure of the speed and clarity of the optical system. It is the ratio of the focal distance to the ...

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

Camera manufacturers sometimes list these equivalents because some photographers are more familiar with 35mm cameras and they want to make it easier to understand. It also gives us a standard of reference for all the different format sizes. They may also list the multiplier factor. For example, the APS-C multiplier is around 1.6x.  So a 32mm lens on an APS-C camera (like the Nikon D3200) would act like a 50mm lens on a 35mm film camera. Does focusing affect the focal length?

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.

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.

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.

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 cameratest

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.

Let’s say you take a picture of an automobile with two cameras, a 35mm film camera and a smartphone camera. You stand in the same spot and take two photos, one with each camera. In both cases you want to take a photo of the automobile that fills the frame. If the 35mm film camera lens has a 50mm focal length, the digital camera’s focal length might be 4mm. So even though they are very different numbers they produce the same result because of the size of the imaging surface. So the “equivalent 35mm focal length” for this smartphone camera at 4mm is 50mm.

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.

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.

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.

Above we mention that focal length is related to focus distance.  Focal length is the principal distance of a camera when it is focused at infinity. In photogrammetry we are interested in the camera’s internal geometry at the time photos were taken – so it is the principal distance that we want to know precisely in photogrammetry.

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.

The focal length number tells us how much of the scene is captured in the picture. The lower the number the wider the view, and the more we can see.  The higher the number, the narrower the view, and the less we can see.   This is illustrated below – where the camera is stationary and the focal length (in white numerals) changes:

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