In photography an aberration is understood to be an image defect resulting from the divergence between the actual object picture and the ideal optical picture.
chromatic Aberration (the variation of a lens's refractive index with wavelength)
Abnormal dispersion (AD) optical lenses help to reduce chromatic aberrations at high light frequencies. By combining AD elements with different lenses made of normal optical glass, it is possible to control the light dispersion of certain wavelengths.
Analogue photography refers to conventional photography based on photosensitive films rather than sensors as in digital photography.
In contrast to conventional photography, digital photography uses electronic photosensitive sensors. These store an image in the form of an electric charge which is subsequently processed by means of a computer processor.
Angle of view
The angle of view describes the angle with which lenses capture an image with sufficiently low image defects.
In the diagram below (diagram 01) the angle of view is α.
For the angle α/2, tan α/2 = d/f d = focal length for the corner f = focal length
Example: If the focal length is equal to the format diagonal, then tan α = 0.5 and therefore the angle is 53°. This is a standard lens for the respective format.
Lenses can be roughly sorted into the following categories:
Telephoto lenses α < 20°
long focal length 20° < α < 40°
Normal lens 40° < α < 55°
Wide-angle lens α > 55°
The evaluation of a lens can only occur when taking into account the format. For example, a normal lens for a certain format can also be used as a long focal length lens for a smaller format. This is particularly relevant in digital photography, because here sensors are used which are smaller than the 35 mm format. Thus, for example, the angle of view of a focal length of 300 mm with 24 x 36 mm negative film corresponds to an angle of view of 480 mm with a sensor of the size 15,2 x 22,7 mm!
The equivalent focal length for 35 mm would be apx. 1.6x longer, because the diagonal format is also apx. 1.6x longer. It seems as though the focal length is longer, but in reality merely the angle of view with small digital (APS-C) sensors becomes smaller.
The following focal length comparison was shot using a 28 mm focal length setting and from the same position. The first picture was taken with a full format sensor and the second with an APS-C sized sensor. The angle of view of the image shot with the APS-C sensor corresponds to a focal length of apx. 50 mm when converted to full format (although the focal length has physically remained constant).
Anomalous Dispersion glass is a special optical glass that delivers an abnormally large partial dispersion ratio (amount of dispersion at a given wavelength range within visible light) relative to a specific wavelength zone. By combining AD glass elements with elements made of normal glass with different dispersion characteristics, dispersion factors of a specific wavelength can be controlled, resulting in effective compensation of on-axis chromatic aberration on telephoto lenses, or lateral chromatic aberration often associated with wide-angle lenses of conventional optical configuration.
The difference in partial dispersion factors between normal optical glass and AD glass elements (schematic diagram).
The aperture (derived from the Latin word aperire meaning "open") is a device which determines the width of the path for incoming light. The opening is mostly often adjusted with the help of overlapping diaphragm blades which are aligned in a circular shape. The more these blades are moved into one another, the narrower the resulting light path and the less light can enter the system and vice-versa.
The aperture controls the level of lighting and together with the exposure time the exposure of the film or chip is regulated. Apart from the exposure time and the viewfinder the aperture is an important technical means of photographic creativity because it influences the depth of field.
The aperture is expressed as a number without dimension derived by the relation between focal length and the width of the lens opening (more exactly: the focal length divided by the diameter of the entrance pupil). The luminosity of the lens corresponds to the smallest f number, so of the biggest relative opening. The f number of mechanical cameras is adjusted on the lens ring, as opposed to electronic cameras where the adjustment is made per control elements on the camera body.
APS-C was originally a film format of the size 25,1 x 16,7 mm (the crop format of the original negative format APS). Nowadays it is often given as a dimension format for image sensors of digital SLRs, because these have a similar scale. Tamron has a series of lenses designed exclusively for this format called Di II.
The abbreviation ASL (ASpherical Lens) refers to hybrid aspherical lens elements. These correct typical imaging errors of zoom lenses, for example spherical aberrations (focus errors). They are suitable for particularly compact lenses, as they favour a more compact design while maintaining the same high imaging quality.
Aspherical means that a lens element is not derived from a sphere in terms of shape. This complex production technique is used to avoid aberrations. An optimum in terms of image quality and compactness is achieved, as several elements can be replaced by one aspherical element when using this innovative technology. Conventional lens elements usually have a fixed radius (spherical), i.e. they can be thought of as being cut from a sphere (sphere). However, this simple lens shape has the disadvantage of introducing aberrations such as aperture aberration, astigmatism, coma and distortion.
Thanks to innovative production techniques, people are now increasingly using aspherical lenses. Generally speaking, these lenses have a surface that deviates from the spherical shape. Especially the aperture error and the coma correction can be greatly improved with these aspheres. In addition, the distortion of lenses can be compensated by means of aspheres. During production, a special plastic is bonded to the surface of the glass to form the aspheres. Tamron masters this technology perfectly and uses these lenses in many of its lenses.
The image below (aspherical lenses) illustrates the difference between a spherical and an aspherical lens. The part marked in yellow is a high-quality plastic that is bonded to the spherical glass body.
Astigmatism (Greek for "dotlessness") is the term used in photography to describe a type of imaging error. Light beams entering at an angle, which should appear as a point in the imaging plane, are distorted into (elliptical) discs. The reason is the difference in focal length between the so-called meridional beam and the sagittal beam. Astigmatism is largely avoided in Tamron lenses through aspherical lens elements as well as through the clever arrangement and combination of glass elements and their deflection as well as optimised aperture position.
Available Light means refers to photography without any additional lighting i.e. a flash in spite of unfavorable lighting conditions (e.g., at dusk or indoors). Instead, the camera sensitivity/speed is increased or lenses with image stabilizer are used (i.e., Tamron VC lenses).
As shown in the two pictures below, the atmosphere of an image can change considerably or can even be destroyed completely if artificial lighting is used.
The left picture (picture 01) was photographed with a flash, the right (picture 02) without.
Broad Band Anti Reflex
Modern multi-layer coating of the highest quality to prevent stray light and ghost images.
As soon as light hits untreated glass surfaces, part of it is reflected. On average, the degree of reflection on untreated glass surfaces is 5 % - 6 %. This leads to "ghost images" and to loss of light and contrast.
To suppress these reflections, Tamron developed the BBAR (broadband, anti-reflective) coating technology, which also ensures the best possible colour balance. This is found in all Tamron lenses. A further developed BBAR coating ensures even better light transmission in the latest lens developments, both at long and short wavelengths.
This reflection reduction is achieved through interference. The technique used here is based on the fact that reflected light waves with the same amplitude and a path difference of λ / 2 cancel each other out. Consequently, layers of magnesium fluoride in the nanometre range are applied to the glass surface, at whose interfaces the light waves are reflected. If one chooses an appropriate layer thickness, the reflected waves cancel each other out and the reflection energy is converted into transmission energy, so that the reflected light wave passes through the lens instead of being reflected.
However, single-layer coatings only act on a limited wavelength range and are not very effective. Only the application of coatings of different thickness and refractive index shows an effective reduction of reflection over a large wavelength range.
The following diagram (Diagram 01) shows an example of this relationship for a particular glass. The reflectance in % is plotted on the left and the wavelength of the light is plotted below. The reflections decrease significantly over the entire wavelength range with several coatings.
The advanced BBAR-G2 coating has been in use since 2019.
Chromatic aberration is an image defect, reducing the sharpness of an image and originating from the unequal refraction of different light wave lengths. The aberration originates particularly in the edges of an image in the form of color fringes.
There are two types of chromatic aberration: longitudinal (typical at long focal lengths) and lateral (typical at short focal lengths).
LD (Low dispersion) glass is used to minimize this mistake. Particularly the photosensitive sensors of digital SLR cameras are sensitive for chromatic aberration; hence, its minimization is especially important in Di and Di II lenses.
The diagram above (Schematic diagram) shows the difference in chromatic aberration between optical glass and LD glass elements.
Coma is an aberration resulting from beams of light which lie beyond the optical axis. The beams of light pass through an off-axis point causing the lens to focus at different points. The picture points are scattered, and appear as a comet-shaped blur.
With imperfect optical systems this grouping occurs asymmetrically. Instead of a sharp airy disk, a picture point with a tail directed toward the edge of the optics occurs. This appearance can be diminished by fading out the edges of the rays.
Depth of Field
The depth of field is the range of acceptable sharpness in which a motive is illustrated sharply. The depth of field depends on 3 factors: the focal length, the aperture and the focused distance. The rule of thumb is: The longer the focal length and the wider the aperture, the less the depth of field.
Unfortunately, the question regarding the depth of field in lenses used together with digital cameras cannot be answered precisely. In general, in contrast to 35 mm film photography, digital photography is influenced by the geometrical nature of the sensor. Nevertheless, in general the depth of field increases with APS-C format sensors in contrast to film, where it remains constant and roughly the same as with full-format sensors. In this case, there is no difference between Di and Di II lenses.
Unfortunately, we cannot make exact depth of field tables available, because we would have to test every lens with every available sensor on the market.
We have tried to show the approximate circumstances with the depth of field tool on our website.
Please note that the calculations of this tool are merely approximate values and do not represent binding specifications. To get extensive control of the depth of field, we recommend using fast lenses, because they offer more creative freedom.
Digitally Integrated Design - A Generation of lenses designed for optimized use with digital SLR cameras
(APS-C format and full-frame) by means of superior designs and multi-coating techniques. The same outstanding performance is also achieved with conventional cameras.
Di II lenses are constructed for the exclusive use on digital SLR cameras with smaller-size imagers
(not bigger than 16 x 24 mm) and featuring optical systems optimized to meet the performance characteristics of digital SLR cameras including:
Minimization of peripheral light fall-off
Minimization of scattered light behavior
Minimization of chromatic aberration.
One example is the application of highly effective multi-coatings on lens and cemented surfaces to eliminate ghosting and flare, which is otherwise particularly noticeable with digital cameras.
At the same time vignetting was minimized, so that digital images are steadily illuminated from the center to the corners. Di II lenses provide ideal focal lengths to cover the range desired by digital photographers and delivering high definition, high contrast-digital images.
Di III (Digitally integrated design): A designation Tamron gives to lenses engineered specifically for mirrorless interchangeable-lens cameras with no internal mirror box or pentaprism, adopting an optical design that matches the characteristics of the digital camera.
* The lens can not be used with digital SLR cameras with a built-in mirror boxor with conventional SLR cameras.
At Tamron, this designation stands for compact lenses that have been specially developed for mirrorless system cameras with APS-C sensors.
Distortion is a form of aberration in which an image defect ocurrs which does not occur true-to-scale.
If the enlargement increases towards the edges of an image field, a square is captured in a cushion-shaped form.
The opposite way is called barrel distortion.
The distortion can be compensated with the help of aspherical lens elements.
TAMRON lenses with Dual MPU (Micro-Processing Unit) have a powerful dual processor that ensures fast processing of the digital signals from autofocus and VC image stabiliser. The lens responds to the camera's commands at lightning speed. The result is very precise focusing, even in dynamic shooting situations, with highly accurate image stabilisation at the same time.
The Dynamic Rolling Cam mechanism ensures fast and precise automatic focusing even with lenses that have relatively heavy focus groups. The innovative technology ensures reliable autofocus performance even in the most demanding professional shooting situations (e.g. extremely cold or hot environments).
The eBAND coating consists of an extremely thin nanostructure (1 nm = 1 / 1.000.000 mm) with a very low refractive index. In combination with the underlying multi-coating, a remarkable anti-reflective effect is achieved.
Curvature of the "focal plane" - In image field curvature, the edges of images become blurred because the image is produced on a curved surface. The cause of this is astigmatism. It causes rays that are far from the axis to be imaged closer to the lens than rays that are close to the axis. This creates two so-called image shells and the image in the desired image plane becomes blurred towards the edges. By cleverly arranging and combining glass elements and their deflection as well as optimising the aperture position, image field curvature is largely avoided with Tamron lenses.
A film plane is the area inside a camera where the film or digital sensor is positioned during exposure, and the focused image is reproduced on the light-sensitive material.
Fixed Focal Length
A fixed focal length lens is a lens whose focal length cannot be adjusted as with a zoom lens.
In comparison to a zoom a fixed focal length lens is simpler and less expensive to develop and produce. Therefore, fixed focal length lenses generally have a better resolution property, better image quality and a higher luminosity.
Light originating from reflections within a lens is called scattered or stray light. This non-intended light within the optical system reduces the image contrast and results in weak colors. This is particularly a problem with digital cameras, because of the very high reflecting property of image sensors.
Different technologies are combined in lens design to decrease undesirable scattered light:
Tamron employed new BBAR (Broad-Band Anti-Reflection) multi-layer coatingson all Di and Di II lenses. This advanced coating was optimized for the special requirements of digital SLRs. In addition, Tamron employs internal surface coatings (coatings on cemented surfaces of lens elements) for sharpness, high color reproduction performance and superior color balance.
Parts of the lens mount which lie in the beam path have as insofar as possible a matt black finish.
Lens hoods reduce the emergence of scattered light, by avoiding the lateral incidence of light in the optic.
Flex Zoom Lock
The FLEX ZOOM LOCK allows the current zoom position to be quickly fixed by moving the zoom ring.
The fluorine coating protects the front lens from dirt and damage.
Grease and water do not adhere to the surface and can be easily removed.
When parallel light rays enter the lens parallel to the optical axis (= infinity setting of the lens), the outgoing light meets at the focal point. The focal length is the distance between this focus point and the principal plane. The focal length is included in the lens name and is specified in millimeters (mm).
The dimensions of the image sensors of full-frame cameras correspond approximately to the 35 mm format (24x36 mm) of analogue SLR cameras.
HID - Glass Element
The HID glass element minimizes chromatic aberration on the axis and in the image corners, one of the biggest obstacles in high optical quality.
HLD-Autofocus (High/Low torque modulated Drive)
The HLD (High/Low torque modulated Drive) autofocus is based on an energy-saving motor with a high drive torque to enable precise and smooth focusing. The arc-shaped HLD unit can be integrated into the lens assembly to save space and allows the construction of compact lenses.
Hybrid aspherical elements are optical glass elements on which special plastics are compounded to give the element an aspherical form.
The incidence of light on a light-sensitive image sensor produces a signal that can be influenced by unwanted disturbance variables (electric fields, light reflections, etc.). This results in a signal-to-noise ratio (SNR), which is a measure of the quality of a useful signal from a source that is overlaid by a noise signal. The noise leads to undesired colour dots in the image, especially in night shots and longer shutter speeds.
The image plane is the area within a camera where the subject is captured as a sharp image. With analogue cameras the image plane is equal to the film plane, with digital cameras it is equal to the image sensor.
In digital photography images are stored on a digital storage medium using an electronic image converter
(picture sensor). There are two types: CMOS (Complementary Metal Oxide Semiconductor) chip sensors which use less electricity, are quick and generate little heat and CCD (Charge Coupled Device) chips which uses more energy, but however delivers a better image quality.
Lenses of customary design have a front lens group which shifts when focusing. Internal focus lenses reach the sharp position by shifting (an) inner lens element(s). Here Tamron has developed the so-called Integrated Focus Cam which allows quick and exact focusing. Moreover, the MFD can also be reduced with the internal focusing, as well as image defects like vignetting. Another advantage is the stationary focus-ring regardless of the zoom position. The front element of the lens also does not turn which is important when using filters which dependent on direction
(e.g., polarization filters).
Lateral Chromatic Aberration
With this aberration different sized pictures originate for different wavelengths of light. This results in color hemlines in the image border.
Glass has the characteristic to break the different wavelengths of light to a different extent. Short wavelengths are more strongly refracted than long wavelengths. This characteristic is called dispersion and leads to undesirable side-effects such as lateral chromatic aberration. In the construction of lenses, emphasis is placed on keeping the dispersion of the overall system very low.
Tamron uses LD (Low dispersion) and AD (Anomalous dispersion) elements to avoid lateral chromatic aberration. These are glass elements which either have low dispersion properties or anomalous dispersion properties for certain wavelengths.
The graphic down below (graphic 01) clearly shows the concept.
Normal optical glass has a relatively high color dispersion index, so that it comes to color hemlines in the image border.
With Tamron LD glass the dispersion is substantially lower, so that color hemlines are minimized in the edges.
The lens hood is an important accessory in photography which prevents unwanted light from striking the lens and causing image flare.
The form of the lens hood depends on the angle of view of the lens and on the diameter of the front lens. A lens with a narrow angle of view needs a longer lens hood than a lens with a wider angle of view. (See example above).
If the front lens does not rotate while focusing or zooming (IF Lenses), the lens hood can be built a little longer. Because, however, vignetting would first appear in the corners, these are left out. This is how the flower-shaped hood got its form. The advantage of this construction, which is used with many Tamron lenses is the improved protection against stray-light at longer focal lengths.
Longitudinal Chromatic Aberration
With longitudinal chromatic aberration the focal point position on the optical axis varies according to the wavelength. This leads to blurred picture points and poor contrast.
Glass has the characteristic to break the different wavelengths of light to a different extent. Short wavelengths are more strongly refracted than long wavelengths. This characteristic is called dispersion and leads to undesirable side-effects, such as longitudinal chromatic aberration. In the construction of lenses, emphasis is placed on keeping the dispersion of the overall system very low.
Tamron uses LD (Low dispersion) and AD (Anomalous dispersion) elements to avoid longitudinal chromatic aberration. These are glass elements which either have low dispersion properties or anomalous dispersion properties for certain wavelengths.
The diagrams down below (diagrams 01) underline the correlation: the first diagram shows the longitudinal chromatic aberration of normal glass. Only the middle wavelengths focus on the image plane. The second diagram clearly shows the reduction of this aberration through the application of LD glass.
LD Elements are produced of special glass materials which possess an extremely low color dispersion index (a unit which measures the ability of a glass to separate a beam of light in its spectral colors). LD elements compensate for chromatic aberration, which is particularly a problem with telephoto lenses. Chromatic aberration is a form of optical noise which reduces the sharpness and the brilliance of an image.
Macro photography is the reproduction of small objects from a magnification ratio of approx. 1 : 4 up to about 5 : 1 (at which point microphotography begins).
Optical systems (lenses) that image an object do so at a certain scale. This ratio of image size to object size is called image scale.
b = image size / object sizeA scale of 1 : 1 means that the object and the image are the same size. A scale of 1 : 2 means that the image is half the size of the object (etc.).
The luminosity is defined by the maximum effective diaphragm opening divided by the focal length of a lens.
Lenses with wide apertures are especially required under unfavorable lighting conditions (interiors without flash, animal photography in the dusk etc.). In addition, fast lenses offer a wider scope of creative potential. Because the size of the diaphragm opening determines the depth of field, conscious and pleasantly blurred backgrounds can be generated with big diaphragm openings, creating dramatic effects by softening surrounding details so the subject seems to “pop” off the background. As a rule stopped-down fast lenses deliver better results than slower lenses at the same aperture setting.
Minimum Focus Distance
The minimum focusing distance is the distance between the object and the film plane or the image sensor of the camera at which a lens still illustrates sharply. The minimum focusing distance together with the focal length determines the magnification ratio.
Modular Transfer Function (MTF)
An MTF diagram represents the contrast and resolution of a lens from centre to edge in relation to an optimal lens that would transmit 100 % of the incident light. The MTF diagram consists of measurements for the sagittal and meridional lines with 10 lines and 30 lines per millimetre.
The optical axis is an imaginary line through the centre of curvature of a lens.
(Simply: the center of a lens).
OSD-Technology (Optimized Silent Drive)
OSD (Optimized Silent Drive) technology is ideal for situations where absolute silence is required when shooting. The OSD autofocus is also particularly responsive and focuses very precisely even when tracking dynamic subjects.
A distinction is made between linear polarisation filters and circular polarisation filters. Linear polarisation filters consist of mechanically stretched plastics with oriented rod-shaped molecules that have been coloured by a dye. Glass-mounted versions are available for lenses. Large-format films are also available for illumination purposes.
The filters convert unpolarised light into polarised light. The extension factor is about 2 - 3. Circular polarising filters are used with cameras that are equipped with metering via mirrors. These can react with measurement uncertainty, as the measuring light can be additionally polarised during redirection. In addition, a circular polarising filter is necessary for autofocus cameras because the linear polarising filter impairs the autofocus function by blocking out light that reaches the AF sensor at certain angles.
The effect of a polarising filter is best seen on a reflecting water surface. The polarising filter has the effect of greatly reducing reflections at a certain position. In addition, polarising filters increase the saturation of colours of reflecting objects.
The blue of the sky also becomes very intense because disturbing stray light from certain angles is eliminated.
With optical systems the beams of light which come from infinity are broken to a certain focus.
The imaginary plane where this happens is called the principle plane. The principle plane must not
necessarily lie within the lens or the optical system.
PZD (Piezo Drive)
Ultrasonic motors are divided into two categories depending on the principle that generates the energy to move the drive: traveling wave motors and standing wave motors. Traveling wave motors include the ring type ultrasonic motor used in the recently launched 70 – 300 mm F/4 - 5.6 VC USD, as well as other lenses, but this lens employs a newer technology, the PZD (Piezo Drive), which functions on the standing wave principle.
A standing wave ultrasonic motor utilizes high-frequency voltage to extend and turn the piezoelectric (piezoceramic) element, thus moving the entire element in a standing wave movement. A metal tip on the piezoceramic element is elliptically rotated by the rotary movement of the element and in turn drives the rotor by means of friction. Standing wave ultrasonic motors have the distinct advantage of being smaller than their traveling wave counterparts, and therefore allow a more compact SLR lens size.
The Tamron Piezo Drive distinguishes with its precise, fast and silent autofocus.
In photography resolution or resolution property refers to the ability of a lens to be able to return certain small detail structures. The resolution is measured in lines per millimetre and is dependent on the position (for physical reasons the resolution is a little worse at the image edges than in the middle of an image). Tamron lenses reach an optimal resolution property over the entire image field due to their construction by means of modern computer design.
RXD-Autofocus-Technology (Rapid eXtra-silent Drive)
The RXD technology (Rapid eXtra-silent Drive) is based on a stepper motor whose drive element controls the ideal angle of rotation precisely and silently. A sensor continuously determines the focus setting of the lens. The powerful RXD motor keeps even dynamic objects continuously in focus.
In photography a shutter is a light-tight, mechanically movable element which lies within a camera in the optical path in front of the image plane. During the exposure time this element is opened for the duration corresponding to the preset shutter speed, in which the light coming from the lens hits the image plane. After exposure has occurred the shutter closes and protects the photosensitive layer of the film material or the digital image sensor against the unintentional incidence of light up to the next shooting.
Spherical aberration is caused by light rays that fall close to the edge of the optics. These light rays are focused at a different distance than centrally incident light rays; the result is a slightly blurred image: the so-called spherical aberration occurs. Nowadays, spherical aberration is mainly corrected by means of aspherical lenses.
Spray Water Protection
Almost all TAMRON lenses have a weatherproof housing. The robust outer casing is effectively sealed against moisture penetration at all critical points (e.g. between focus ring and barrel or at the bayonet mount). This guarantees reliable functionality even in the most adverse outdoor shooting conditions.
This special Tamron designation identifies lenses with exceptional construction and outstanding optical performance.
TAMRON Lens Utility
The TAMRON Lens Utility - Software was developed by us to configure our own TAMRON lenses. After installing the programme on a computer, compatible lenses can be connected to the computer via a connecting cable in order to individually adjust various functions of the lens or to update the lens firmware. Various functions can be activated via the focus button.
With the TAP-in console and the free TAP-in Utility software, the firmware of compatible lenses can be updated and the functionality of the lenses can be individually adjusted. Among other things, settings can be made that previously could only be done on-site at the TAMRON service department. The configurable parameters include: Focus adjustment, setting of the focus limiter, optimisation of the manual focus function and adjustment of the VC image stabiliser.
Tele-converters are additional devices that are attached between the lens and the camera and increase the focal length of the existing lens. The number given indicates the ratio in which the focal length of the lens used is multiplied, e.g. a 2x teleconverter doubles the focal length of the lens.
Teleconverters are therefore often an inexpensive alternative to an additional lens. The disadvantage is that the light intensity of the basic lens is reduced in the same proportion as the increase in focal length. For lenses with a longer focal length, wide-angle lenses and so-called superzooms, the image quality suffers greatly with converters. The use of converters is not recommended here.
USD (Ultrasonic Silent Drive)
Ultrasonic Silent Drive (USD) is a Tamron proprietary development. The fast focusing is suitable for photographing sports, races, or other fast-moving subjects. With advanced motor technology and newly developed software, the Tamron USD delivers accurate and silent focusing at turbo speed.
Tamron's proprietary USD technology uses high-frequency ultrasonic vibrations generated by a fixed ring called a 'stator'. The energy resulting from the vibrations is used to rotate a moving ring of metal known as the 'rotor'.
Piezoelectric ceramics, an element that generates ultrasonic vibrations when the current voltage of a certain frequency (resonant frequency) is applied, were arranged in ring formation on the stator. This electrode configuration of piezoelectric ceramic causes two ultrasonic vibrations on the stator.
By effectively combining both ultrasonic vibrations, it is possible to convert the energy from the simple movement of the vibrations into an energy known as "deflecting travelling waves", which then moves around the circumference of the ring in the direction of rotation.
The focus lens, which is connected to the rotor, is moved in this way and ensures a fast and smooth autofocus drive.
Vibration Compensation (VC)
The VC (vibration compensation) mechanism is a Tamron development which ensures an effective compensation for camera vibrations. Especially hand-held, low-light and tele photography is susceptible for camera shake and consequent blurred results, due to the required longer shutter speeds. Under these photographic conditions the VC mechanism can unfold to its full efficiency.
The construction principle
The VC mechanism includes a VC lens elements which moves parallel to the image plane merely via electronic control (See illustration 1). The driving coil unit includes a a position detector which assesses the respective position of the element VC and reports to the control unit. The VC element has three magnets which are driven by corresponding driving coils. In the control unit, two gyro sensors are installed, which grasp the horizontal and vertical vibrations and report them to the micro processor. The VC element is free-floating (two degrees of freedom, and parallel to the image plane) and can therefore compensate for vibrations in all directions.
If vibrations occur as shown in illustration 2, a blurred picture originates on the image plane, proportionate to the rotation angle of the vibrations. The gyro sensors grasp the respective vibrations and report the data to the microprocessor. This in turn calculates the rotation angle and passes on the respective control commands to the driving unit which in turn shifts the VC element to counter the direction of the vibration. (The system works at a speed of 4 kHz, meaning that a correction is performed 4000 times a second).
Extremely short response times of the driving unit
The VC driving unit uses a three-coil system developed by Tamron. The VC element is magnetically held in position, stored on three steel ball bearings. Since the VC compensating lens element is held in place solely by contact with these bearings, smooth, virtually frictionless movement is assured, providing stabilized viewfinder images and excellent tracking performance characteristic of VC lenses. The result is an extremely short response time on grasped vibrations. Moreover, since the VC lens element moves parallel to the image plane via electronic control alone, the mechanical structure is simplified, and the lens is more compact. This serves the compact design concepts which distinguish Tamron lenses.
A distinction is made here between natural and artificial vignetting. Artificial vignetting is caused by components such as diaphragms, mounts, etc. that protrude into the optical path. These have to be dimensioned accordingly when building the lens. With natural vignetting, the illuminance decreases towards the edge of the image.
VXD-Autofokus (Voice-coil eXtreme-torque Drive)
The VXD autofocus features the world's first linear focus motor developed by TAMRON and offers superior autofocus performance. Two VXD modules, acting in a floating system and controlled by electronic pulses, ensure lightning-fast, precise and whisper-quiet focusing. The technology also guarantees improved AF tracking, for example in sports shots.
In photography, a wide-angle lens is understood to be a lens with an angle of view greater than 55°. In order to cover more subject area, a wide-angle lens illustrates smaller. A wide-angle reduces the image scale.
XLD (Extra Low Dispersion)
An XLD (Extra Low Colour Dispersion) element is made of special glass materials that have an extremely low colour dispersion index (a measure of a glass's ability to separate a beam of light into its spectral colours).
The dispersion properties are even lower than standard LD (Low Dispersion) lenses, and are about the same as fluorites. The XLD lens in combination with the LD element provides the highest contrast and brilliance. This effectively prevents the chromatic aberration that is problematic in telephoto photography and ensures maximum sharpness even in the peripheral areas. The result is a lens that effectively compensates for longitudinal chromatic aberration and axial magnification errors throughout the zoom range.
XR (Extra Refractive Index Glass)
Extra Refractive Index Glass
XR Glass is a special type of glass with a high index of refraction. XR Glass allows for a more compact lens construction in terms of length and diameter, as compared to a lens made of customary glass with the same luminosity and optical performance. The focal length of an XR glass element is shorter than that of customary glass, so that the barrel of an XR lens can be shortened. As a result of the shortening of the barrel, the actual opening consequently becomes bigger and the lens diameter can also be reduced (see picture). The luminosity of the lens remains the same in spite of the smaller diameter.
Fig.: Looking through two barrels of different length and the same diameter, the apparent opening of the shorter barrel is bigger. Therefore the diameter of the shorter barrel (with a constant apparent diameter) can be reduced.
A lens in which you can adjust the focal length is called a zoom or a zoom lens. The advantage of a zoom lens is that the frame can be varied without changing your location as the photographer. Zoom lenses have become indispensable. Tamron has achieved an image performance in its zoom lenses which comes close to those of fixed focal length lenses through its ongoing efforts in research and development (e.g., LD - AD - as well as aspherical elements).
The zoom lock (ZL) mechanism is an extremely useful and much appreciated mechanical concept developed by TAMRON. This feature prevents undesired extension (creep) of the lens barrel when carrying the camera/lens unit on a neck strap. This enhances responsiveness in the field and helps protect the lens.