Tamron Di Lenses
Just What Does Di Mean

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The 28-75mm Di zoom focused very quickly, particularly when used with a camera with an advanced AF system. That combination makes this lens ideal for capturing a fleeting moment, without the frustration produced by some equipment that often hunts for focus. (Canon EOS 10D; at 75mm; f/2.8 at 1/125 sec; ISO 100; image cropped slightly.)
© 2003, Peter K. Burian, All Rights Reserved

Tamron's New SP AF 28-75mm F/2.8 XR Di LD Aspherical [IF] Macro And SP AF 180mm F/3.5 Di LD (IF) 1:1 Macro Lenses

First announced at the photokina show in October 2002, Tamron's "Digitally Integrated" series of lenses began shipping in the summer of 2003. Developed to solve some of the problems caused by conventional lenses when used with digital cameras, the Di series is equally appropriate for use with 35mm SLRs. Initially, five lenses will be available: the SP AF 17-35mm f/2.8-4 Di LD Aspherical [IF], the SP AF 70-200mm f/2.8 Di LD [IF], the SP AF 200-500mm f/5.6-6.3 Di LD [IF], and the two that I tested. During trips to New York, Ottawa, and Quebec City, I worked extensively with the SP AF 28-75mm f/2.8 XR Di LD Aspherical [IF] Macro zoom and the SP AF 180mm f/3.5 Di LD (IF) 1:1 Macro.

Di Lens Technology
Before discussing my evaluation of the two lenses, let's consider the technical issues that led to the development of the Di series. With most conventional lenses, light reflected from the subject strikes the image plane at an increasingly oblique angle as you move toward the edges of the image. This can produce some darkening at the edges of the frame when film is used, and is most noticeable with wide angle lenses used at wide apertures.

Although the Di technology was developed for improved performance with digital SLRs, the sophisticated optical formula produces excellent results with film cameras as well. Most of my 35mm slides are razor sharp across the entire frame and exhibit high contrast and resolution of fine detail. (Canon EOS-3;
28-75mm Di zoom at 28mm; f/8 at 1/250 sec; Hoya polarizer; Fujichrome Velvia 100F film.)

The CCD and CMOS sensors used in digital cameras are designed for optimum results with light that strikes all pixels at a 90Þ angle. Because of peripheral light falloff, less light reaches the pixels at the edges of the sensor. This can produce uneven brightness or vignetting. The problem is minor with some conventional lenses and more serious with others.

While Tamron will not release proprietary information as to the Di technology, a tech rep provided some specifics, summarized as follows. The optical design increases peripheral light gathering capability for increased "corner luminosity." The Di lenses also include new optical configurations and superior anti-reflection coatings. These measures compensate for another problem identified by Tamron engineers: flare, including ghost images in extremely bright situations.

In order to maximize overall image quality and convenience of operation, the Di series offers other useful features. Depending on the specific lens, at least one type of special glass is used to compensate for optical aberrations and distortion, to optimize color rendition and to focus all wavelengths of light accurately, for sharpness across the entire frame. To minimize weight, the barrels include components of engineering plastics said to "excel in dimensional stability and strength." The three telephoto models include a bonus: a Filter Effect Control (FEC) ring on the barrel. This ring can be used to rotate a polarizer while the lens hood is attached, a highly convenient arrangement in outdoor photography. Naturally, all of the optical and mechanical amenities are beneficial with any type of camera, making the Di lenses highly appropriate for use in film-based photography as well.

At both 28mm and 75mm, the Tamron Di zoom produced excellent image quality. Even at a wide f/5.6 aperture, the images exhibit high sharpness across the frame and no visible darkening at the edges. (Canon EOS 10D in raw capture mode; ISO 400; Hoya polarizer; at f/5.6 at 1/500 sec.)

The 28-75mm Di Zoom
Billed as the "world's lightest and most compact fast standard zoom lens" the new Tamron SP AF 28-75mm f/2.8 XR LD Di Aspherical [IF] Macro zoom is surprisingly small for an f/2.8 model. When zoomed to 75mm, the internal barrel extends by 1.5", but the overall length is still shorter than average. Nicely finished in matte black, the barrel features a rotary zoom mechanism, wide, rubberized focus and zoom rings, and a focal length and distance scale. The manual focusing ring is quite well damped, with enough friction for convenient operation. Zooming action is adequately stiff so I found no need for the lock mechanism that can prevent the barrel from extending when the lens is pointed upward or downward. Although the focus ring rotates during AF operation, focus response is fast and fairly quiet; thanks to the wide maximum aperture, the system was reliable even in the low light.

As noted in our Specs chart, the 28-75mm Di zoom incorporates three types of special glass elements for optimum image quality at all focal lengths.

At all focal lengths and all f/stops, this lens produced digital images and color slides with very high contrast, sharpness, clarity, and resolution of fine detail. Particularly in the mid range of focal lengths, and especially at f/4-f/11, image quality is superlative. Edge sharpness matches central sharpness, impressive performance with any zoom lens. Flare was very well controlled, a real benefit on sunny days in extreme sidelighting. In all of my images, brightness is consistent across the entire frame, at all focal lengths, from f/4-f/22. My best digital images made for exhibition quality 11x17" ink jet prints and my Velvia 100F slides are also technically exceptional.

Evaluation: All in all, I considered this 28-75mm Di lens to be an ideal "standard" zoom with the EOS 3 because of its compact size, modest weight, and high-tech optical formula. When mounted on the EOS 10D, with an image sensor smaller than a 35mm film frame, the effective focal length was 45-120mm. That's still useful, but I would also want the 17-35mm f/2.8-4 Di zoom for subjects that would benefit from a wider angle of view.

Take steps to prevent camera shake and subject motion, and the 180mm Di lens will produce impressive image quality in high-magnification photography. Even at maximum magnification, sharpness is high across the entire frame and resolution is uniformly excellent. (Canon EOS 10D in raw capture mode; f/11 at 1/4 sec; ISO 400; tripod.)

The 180mm Di Macro Lens
A large and moderately heavy lens, the new SP AF 180mm f/3.5 Di LD (IF) 1:1 Macro offers a more professional look and feel. This one includes two low dispersion glass elements to correct chromatic aberration, the Filter Effect Control ring, plus internal focusing to ensure consistent length and balance, important with a long lens. The focus ring does not rotate during AF operation. Models in Canon and Nikon AF mount can be switched between AF and manual focus by sliding a ring on the barrel; with Minolta Maxxum cameras, the AF/MF switch on the camera must be used. The lens hood is very large and long, shading the front element effectively.

A true macro lens, the 180mm Di can reproduce a tiny subject life size on film, and even larger on a digital sensor that's smaller than a 35mm frame. Maximum magnification is available at a focusing distance of 18.5", so there's no need to get excessively close to a subject, an advantage especially in nature photography. In order to maximize the lens' potential in high-magnification work, it's important to use a very sturdy tripod to prevent camera shake. With a moving subject a high ISO setting is also required for fast shutter speeds to prevent motion blur.

To eliminate any vibration or movement, I used a large Bogen/Manfrotto tripod, an ISO 400 setting, and reflex mirror lockup to photograph stamps and currency fastened firmly to a wall. Manual focusing allowed for pinpoint control and the mechanism offered plenty of friction for a familiar feel. The resulting EOS 10D images--made at various levels of high magnification--are razor sharp at all apertures from f/5.6-f/16. They exhibit snappy contrast and remarkable resolution of the most intricate detail even at the edges of the frame; no vignetting is visible in any of my images.

Although this is a macro lens, it's just as useful as a telephoto for more distant subjects. When used with a digital camera with an image sensor smaller than a 35mm film frame, the equivalent focal length is a full 270mm or 280mm. My Velvia slides and EOS 10D images of people, go-carts, and statues exhibit consistent brightness. They're also incredibly clear, contrasty, flare-free, and sharp across the frame even at the wide apertures that I used for fast shutter speeds.

Evaluation: In terms of its construction, mechanical components, and optical design, this is a professional-caliber lens with only one drawback. Autofocus is a bit slow when changing from close to distant focus because the internal mechanism must rotate a great distance; this is typical of many true macro lenses. In all other respects, the 180mm Di is a very desirable lens with great potential in macro and telephoto photography.

Final Evaluation
Both of the Tamron "Digitally Integrated" lenses produced 35mm slides that I would be proud to submit to my stock agency. But did the Di lenses produce better results than conventional lenses when used with the EOS 10D? Most of my digital images are technically superb, but I cannot provide a definitive conclusion based on field testing. Frankly, that determination could only be made with a fully equipped optical lab. It would require scientific comparison testing with several similar lenses--with and without the Di technology--particularly wide angle zooms used at wide apertures.

Nonetheless, I can offer the following assessment; it's based on my testing of the first two lenses, briefly handling the others, and reviewing their impressive technical specifications. The "Di" series should prove to be the best that Tamron has ever produced, helping to enhance the reputation of the brand. Whether you own a 35mm or digital SLR camera, you should certainly check out the Di lenses if you're a serious photographer who insists on top quality and the latest technology.

For more information, visit Tamron's website at www.tamron.com.

Technical Specifications
SP AF 28-75mm f/2.8 XR Di LD Aspherical [IF] Macro
Optical Construction:
16 elements in 14 groups; includes XR (Extra Refractive Index) element, four hybrid aspherical elements, and three LD elements
Mechanical Design: Internal focusing; seven-blade diaphragm; zoom ring lock mechanism
Minimum Focus Distance: 13"
Maximum Magnification Ratio: 1:3.9 at 75mm
Dimensions/Weight: 3.6x2.9"; 18 oz
Filter Mount: 67mm
Street Price: $329 with lens hood
Available AF Mounts: Canon, Minolta, Nikon-D, Pentax

SP AF 180mm f/3.5 Di LD (IF) 1:1 Macro
Optical Construction:
14 elements in 11 groups; two LD elements
Mechanical Design: Internal focusing and floating element; one-touch AF/MF switching (Canon and Nikon mount); filter rotating ring on barrel; seven-blade diaphragm
Minimum Focus Distance: 18.1"
Maximum Magnification Ratio: 1:1
Dimensions/Weight: 3.3x6.5"; 2 lbs
Filter Mount: 72mm
Street Price: $699 with lens hood and tripod mounting collar
Available AF Mounts: Canon, Minolta, Nikon-D

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