|XR (eXtra Refractive index glass)|
Extra Refractive Index
More compact lenses with superior image quality
XR (Extra Refractive Index) glass can bend light rays at steeper angles, thereby decreasing the physical length of the lens while enhancing imaging performance by minimising optical aberrations. With its superior light-bending power, XR glass makes it possible to design a short-barrel lens with the same light-gathering ability (aperture value) as a long-barrel lens – even with a smaller lens diameter. By using this principle Tamron has been able to shorten the length of the entire optical system and produce lighter, more compact lenses of the same speed, and also to provide greater zoom ranges in lenses that are much more convenient to carry and hand-hold.
XR glass is costlier than conventional glass but it yields enhanced optical power distribution, making the innovative XR lens designs possible.
Focusing elements inside the optical design make for better handling
In many lenses, the front elements move back and forth to alter the focus distance. With an internal focusing (IF) mechanism, the focusing elements are inside the optical design. Because the front lens elements remain static, the lens’ actual length does not change. This provides several benefits both to the image and during photography:
- The barrel is not subject to stray light entering from external helicoids that can adversely affect image quality
- A non-rotating front filter thread makes it easier to use filters such as graduated filters and polarisers
- A flower-shaped lens hood will remain in the correct position to most effectively shield the lens from stray light
- Better balance and more predictable handling because the lens length does not change during focusing
- Generally, a much closer minimum focusing distance throughout the zoom range
- Improved optical performance by minimising loss of illumination at the corners of the image field (vignetting)
- Suppression of other aberrations that become more troublesome at different focusing positions.
Integrated focus cam optimises internal focusing
Tamron's Integrated Focus Cam is a precision mechanical component that optimises the co-ordinated movement of the Internal Focusing (IF) system with the Multiple Cam Zoom Mechanism. This ingenious mechanism ensures accurate and seamless positioning of all the internal elements within the lens and coordinates them with the external zoom and focus controls.
Far superior image quality – while reducing lens size and weight
Tamron uses several hybrid aspherical lens elements in its lenses bearing the Aspherical designation. The benefits are two-fold: first, their non-spherical shapes virtually eliminate spherical aberration and image distortion. Second, as one hybrid aspherical lens element can take the place of multiple elements without compromising performance, they allow the lens to be much more compact.
As a result, these innovative optics have played a crucial role in delivering uniformly high image quality across all apertures and focal lengths of extraordinarily compact ultra-zoom lenses.
Sharpens edges by reducing 'colour fringing'
Chromatic aberration occurs when a lens element refracts different wavelengths of a ray of light – its rainbow colours – at very slightly different angles. This results in the 'colour fringing' that reduces the sharpness of an image. LD elements are made from special glass materials with extremely low dispersion indices (i.e. the refraction of a ray of light into rainbow colours is extremely narrow). Thus they effectively compensate for chromatic aberration at the centre of the field (on axis), a particular problem at long focal lengths (the telephoto end of the zoom range), and for lateral chromatic aberration (toward the edges of the field) that often occurs at short (wideangle) focal lengths.
Although costly, LD glass materials result in clear, vivid image quality.
Internal surface coatings reduce ghosting and flare
Tamron has adopted various countermeasures against the problem of ghosting and flare caused by aberrations. Internal surface coatings (i.e., multiple-layer coatings on cemented surfaces of plural elements) and new multiple-layer coating technology on ordinary elements, minimise reflections as light enters through the front element and reduce image-degrading effects caused by the imaging sensors themselves.
Dedicated for digital SLR cameras
By incorporating an optical design for exclusive use with digital SLR cameras with smaller-size imagers, this high-power zoom lens provides the same focal length, when converted to a 35mm format, equivalent to Tamron's 28-300mm. Therefore, you can meet virtually every photographic opportunity with this single zoom lens without changing lenses. When paired with a wideangle zoom, you can thoroughly enjoy digital SLR photography with a combined equivalent focal length coverage of 27-300mm.
Enhanced peripheral illumination
Peripheral light fall-off is minimised when compared with that of conventional lenses for film cameras so that images are uniformly bright from the centre to the periphery.
Since the lens is designed exclusively for digital SLR photography, it provides high image quality in terms of resolution, contrast and flatness of image field.
Revolutionary minimum focus distance – 45cm (17.7") for 1:3.7* macro capability
It is important for a multi-purpose zoom lens to be able to get close to small subject. The new optical/mechanical design configuration of this lens allows an MFD (Minimum Focus Distance) of 45cm (17.7"). At 200mm the maximum magnification ratio is 1:3.7*, close-up photography is easy and convenient.
* The Maximum Magnification Ratio of this lens is 1:3.7 while the Maximum Magnification Ratio of the AF28-300mm (Model A061) is 1:2.9. However, the 18-200mm can fill the frame with almost the same scope as the A061 does when shooting with a 35mm SLR camera, since the new lens is exclusively designed for digital SLR cameras with smaller-size imagers. The Maximum Magnification Ratio of 1:3.7 is equivalent to 1:2.8 when converted to 35mm film format.
High power, yet compact and lightweight thanks to newly developed mechanisms
New and complex mechanisms are hidden in this lens' compact construction. Several engineering innovations were required to downsize the design, produce high-precision parts and increase durability, imbuing this multi-purpose zoom lens with excellent portability and ease of use.
Flower-shaped hood is supplied with the lens to shield stray light
Included as a standard accessory, the flower-shaped hood matches the rectangular shape of the image sensor to most effectively block the interference of superfluous light rays entering from outside the borders of the image area, helping to ensure sharp, clear, flare-free images with crisp detail in the shadow areas.
Useful when carrying the lens/camera over the shoulder
Another original Tamron mechanical engineering concept is the zoom-lock mechanism, which prevents the weight of the lens barrel from extending the lens when carried on the camera pointing downward. This eliminates the danger of accidentally knocking the lens while walking around and enhances responsiveness in the field. Simply zoom the lens out to its widest focal length and use the sliding zoom-lock switch to lock the barrel in place.
New external design on the Di-II series conveys "high-performance, high-precision" image
The external appearance has been enhanced with a gold-coloured band between the focus and zoom rings, marking it distinctively as a Tamron Di II lens. New rubber patterns of the zoom and focus control rings complement the digital camera design style and provide improved handling.
|Angle of view||75° 33' - 7° 59'|
|Lens construction||15 elements in 13 groups|
|Minimum focus distance||0.45m (17.7 in.)|
|Maximum magnification ratio||1:3.7 (at f=200mm MFD 0.45m)|
|83.7mm (3.3 in.)*|
|Maximum diameter||φ73.8mm (2.9 in.)|
|Weight||398 grams (14oz)*|
|Standard accessory||Flower-shaped lens hood|
|Mounts available||Canon AF, Sony (Konica Minolta), Nikon AF-D, Pentax AF|