Although Tamron's SP AF 28-75mm f/2.8 XR Di LD Aspherical [IF] lens has been designed for cameras with 36 x 24mm sensors, it is also usable on cameras with smaller, APS-C sized sensors, where it covers a focal length range of 44.8-120mm on Canon DSLRs or 42-112.5mm on all the rest. The fast f/2.8 maximum aperture applies throughout the 2.7x zoom range with both sensor sizes.
Tamron's SP AF 28-75mm f/2.8 XR Di LD Aspherical [IF] lens, shown in side view without the supplied lens hood. (Source: Tamron.)
One of Tamron's SP (Super Performance) lenses, it has been designed and constructed to ‘professional quality' standards. The optical design is relatively complex, with 16 elements in 14 groups, including two XR elements, four hybrid aspherical elements and three LD (Low Dispersion) glass elements. The Di tag indicates it has been designed to meet the performance characteristics of DSLR cameras while covering the image circle of 35mm film.
The above diagram shows the position of the various elements in the lens. (Source: Tamron.)
The inclusion of two XR (eXtra Refractive index) elements, which refract light more efficiently than conventional glass, has enabled Tamron to make this fast lens very compact, reasonably light and affordably priced. No mention is made in Tamron's specifications - or press release - of anti-reflection coatings, although it's safe to assume at least some of the elements are coated to minimise flare and ghosting.
However, some compromises have been made to meet these requirements. There's no built-in stabilisation and focusing is driven by a conventional micro-motor which is noisier than and not quite as fast as Tamron's HSM ultrasonic drives. However, it will be efficient enough for most potential purchasers of this lens.
Build quality is good for the price tag. Most of the barrel is made from high-quality black polycarbonate and the lens has a solid stainless steel mount plus the characteristic gold ring between the focusing and zoom rings. A petal-shaped lens hood is provided, along with front and rear caps. This lens accepts 67 mm diameter filters.
The minimum focusing distance is 33 cm across the entire zoom range. This provides a maximum magnification of 1:3.9 with the 75mm setting. Although this is not true macro performance, it provides adequate scope for close-ups. In addition, the fast f/2.8 maximum aperture provides excellent opportunities for sharp, handheld, close-up photography at slow shutter speeds and gives good control over depth-of-field in close-up shots.
Handling
The review lens felt equally comfortable on the Canon EOS 5D and EOS 40D bodies we used for our tests. Attaching it was straightforward and the solid metal mounting plate fitted very snugly to the camera body. The petal-shaped lens hood, which attaches to the front of the lens via a bayonet fitting, was also a snug fit, which made it tricky to attach at times.
At the 28mm focal length, the lens protrudes 92 mm from the camera body, extending to just under 130 mm at the 75mm focal length position. Internal focusing means the barrel doesn't extend during autofocusing, facilitating the use of angle-critical attachments like polarisers and graduated filters.
The focusing ring is a 23 mm wide band just back from the front of the lens. A distance scale in metres and feet is stamped in white on its leading edge. Behind it is a 13 mm wide ridged rubber band, which provides a secure grip. In manual mode, this ring turns through a very short arc (roughly a quarter of a turn), which leaves little scope for precise manual focusing.
The 42 mm wide zoom ring is located just behind the focusing ring and carries the definitive gold band at its leading edge. Just behind the gold band is a 28 mm wide deeply-ridged, rubberised grip. Five focal length markings (28mm, 35mm, 50mm and 75mm) are stamped in white on its trailing edge. To the right of the 28mm mark lies the zoom lock, which can be set to keep the lens retracted when it's carried on a camera.
A single slider switch on the main barrel close to the camera body allows users to switch between auto and manual focusing. Unfortunately, the focus ring rotates in AF mode, although autofocusing is fairly smooth. However, the micro-motor drive means it's far from silent.
Performance
Although we used both the EOS 5D and EOS 40D camera bodies during the testing period, our Imatest tests were carried out on the EOS 5D body, in line with our other tests of lenses designed to suit the ‘full frame' sensor format. Although our tests showed the review lens suffered from edge and corner softening at all apertures and focal length settings, centre resolution was very high at most apertures (with the exception of the widest and smallest aperture settings).
We measured excellent resolution at all focal lengths between f/3.2 and f/13, after which diffraction began to influence performance, leading to a slow decline to f/22. The graph below shows the results of our tests.
Lateral chromatic aberration was negligible at almost all apertures for the focal length settings, sliding into the ‘low' band for the two shorter focal lengths. In the graph of our Imatest test below, the red line marks the border between ‘negligible' and ‘low' CA.
No significant coloured fringing could be seen in test shots and backlit subjects were competently handled. The only way to make this lens flare is to point it directly into the sun. Vignetting was quite obvious at the widest lens apertures with all focal length settings. Edge darkening was measured at more than 1.5 EV at f/2.8 but stopping down to f/4 effectively eliminated it.
As expected for a wide-angle lens, we found some barrel distortion in shots taken with the 28mm focal length setting but by 35mm the problem was largely resolved. Very slight pincushion distortion was detected at the 75mm focal length setting.
The review lens delivered attractive bokeh for its specifications and price tag. Out-of-focus blurring was mostly smooth. Traces of outlining around the brightest out-of-focus highlights at the widest lens apertures had largely disappeared by f/4.
Test shots taken with the EOS 40D body (which has an APS-C sized sensor) suggest resolution is at least as high with smaller-sensor cameras. However, edge softening was only slightly reduced and vignetting was marginally less.
Buy this lens if:
- You want a fast standard zoom lens with excellent performance for use on ‘full frame' and ‘APS-C' DSLR cameras.
- You'd like a lens that requires no readjustment when you fit polarisers and graduated filters.
- You want attractive bokeh at wide apertures.
Don't buy this lens if:
- You require built-in image stabilisation.
- You want excellent edge-to-edge sharpness.
- You need true macro capabilities.
IMATEST GRAPHS
(based on JPEG files from the Canon EOS 5D)
SAMPLE IMAGES
Vignetting at 28mm f/2.8.
Vignetting at 35mm f/2.8.
Vignetting at 50mm f/2.8.
Vignetting at 75mm f/2.8.
Distortion at 28mm.
Distortion at 75mm.
EOS 5D, 28mm focal length, 1/125 second at f/8, ISO 100.
EOS 5D, 35mm focal length, 1/125 second at f/8, ISO 100.
EOS 5D, 50mm focal length, 1/150 second at f/8, ISO 100.
EOS 5D, 75mm focal length, 1/160 second at f/8, ISO 100.
EOS 40D, 28mm focal length, 1/100 second at f/8, ISO 100.
EOS 40D, 35mm focal length, 1/100 second at f/8, ISO 100.
EOS 40D, 50mm focal length, 1/100 second at f/8, ISO 100.
EOS 40D, 75mm focal length, 1/125 second at f/8, ISO 100.
EOS 5D, 44mm focal length, 1/25 second at f/10, ISO 100.
100% crop from the above image showing edge softening and the relative absence of coloured fringing.
EOS 5D, close-up at 59mm focal length, 1/332 second at f/2.8, ISO 100.
EOS 5D, close-up at 75mm focal length, 1/395 second at f/2.8, ISO 100.
EOS 40D, close-up at 75mm focal length, 1/60 second at f/2.8, ISO 200. Flash fill.
EOS 40D, close-up at 75mm focal length, 1/60 second at f/4, ISO 200. Flash fill.
EOS 5D, 75mm focal length, 1/25 second at f/8, ISO 100.
EOS 40D, 35mm focal length, 1/30 second at f/8, ISO 100.
EOS 40D, 28mm focal length, 1/100 second at f/9.1, ISO 100.
EOS 40D, 75mm focal length, 1/125 second at f/6.4, ISO 100.
EOS 40D, 75mm focal length, 1/166 second at f/4, ISO 200.