These rugged lenses provide several advantages thanks to their wide, and constant, f/2.8 maximum aperture and VC stabilizer.

Article & Images By Peter K. Burian

Because most digital SLR camera owners demand compact, lightweight lenses, the vast majority of zooms feature a small maximum aperture. A typical zoom lens is designated as f/3.5-5.6 indicating that the maximum aperture is quite small at the short end and becomes very small at longer focal lengths. The larger the numeral, the smaller the opening in the lens and the less light that will reach the camera's digital sensor. In practical terms, that translates to moderate light gathering ability for significant advantages as discussed in a moment.

Some zoom lenses feature a wider maximum aperture of f/2.8; ideally, that should be constant, not diminishing as you zoom. For a long stock photography trip through Europe with a full-frame Nikon D800 DSLR, I took three such lenses: the pro-calibre Tamron f/2.8 Di USD VC zooms equipped with an image stabilizer: the 15-30mm, 24-70mm and 70-200mm model. In addition to the availability of f/2.8 at all focal lengths, this trio features very rugged construction and a moisture-resistant design. The latter aspect was certainly useful whenever I was shooting in rain, as I did for an entire evening in the historic centre of beautiful Prague, Czech Republic.

Wide Aperture Benefits

Serious photographers appreciate wide aperture lenses for their greater light-transmitting ability particularly in low light situations. When shooting indoors without flash for example, an f/2.8 lens allows for using faster shutter speed without the need to set a very high ISO level. That's why lenses of this type are called "fast". They can be valuable in producing sharper photos with less blurring from camera shake and/or subject motion. Autofocusing is also quicker and more reliable in dark locations because a wide aperture lens transmits more light to the AF sensor.

An image made at a lower ISO level will exhibit less digital noise: the "grainy" pattern of random, coloured specks that can obliterate intricate detail. While Noise Reduction processing (in the camera or in software) can provide smoother high ISO images, the effect is achieved by blurring the "grain" pattern. That also smudges fine detail reducing resolution. On the other hand, a low ISO image will be "cleaner" with greater resolution of intricate detail.

In addition to providing a brighter view of the subject in the viewfinder, f/2.8 also allows for images with shallower depth of field (selective focus). Especially at focal lengths of 135mm or longer, it's possible to render a cluttered background as a soft blur of color which is less distracting. The effect is most obvious when the subject is no more than two meters from the camera. When it's sharply framed against a soft backdrop, the centre of interest immediately attracts and holds the viewer’s attention.

The "Fast" Tamron Trio
All three f/2.8 lenses offer fast Ultrasonic Silent Drive AF, manual focus override in AF mode, high-grade optics and advanced multi-layer coatings to resist flare. Models in the Canon and Nikon mount are also equipped with a Vibration Compensation stabilizer to minimize the effects of camera shake. Since a tripod is not allowed in cathedrals and palaces, such as Stephansdom and Schönbrunn (Vienna, Austria), the roughly 4 shutter speed step stabilization was a definite asset. This f/2.8 trio was designed for full-frame DSLRs but the lenses are also compatible with DSLRs using the more typical smaller sensors.

Tamron SP 70-200mm f/2.8 Di VC USD
Slightly smaller than others in its class, this tele zoom with solid construction boasts one piece of Extra Low Dispersion glass and four Low Dispersion elements. A removable tripod mounting collar is included. The high tech optical elements minimize chromatic aberrations so even my images made at f/2.8 exhibit no apparent colour fringing, as well as very high sharpness in the central 70% of the image area. At most focal lengths, stopping down to f/4 or a smaller aperture ensured that edge sharpness was also outstanding. For stunning, pro calibre sharpness across the frame at 200mm however, I stopped down to f/5.6 or f/8. While there is some vignetting (darkening at the corners) as with nearly all zooms, this is minimal by f/5.6. Note too that most current imaging software provides a feature that can correct vignetting.

Tamron SP 24-70mm F/2.8 Di VC USD
A relatively portable "standard" zoom with internal focusing and the most popular focal lengths on a full-frame DSLR, this was my most frequently-used lens in Europe. It includes three Low Dispersion elements, three Glass Molded Aspherical plus a Hybrid Aspherical lens and two pieces of Extra Refractive Index glass to compensate aberrations and distortion.

At maximum aperture, sharpness in the central area is high, and by f/4 edge sharpness is equally impressive. There's some vignetting at wide apertures (easily solved later in software) but disappears by f/5.6. The 24mm focal length provided a wide field of view, adequate for most interiors. Some barrel distortion was visible at the shortest focal lengths, as with most such zooms, also easily corrected with software. The 70mm end was perfect for portraits. All in all, this lens provided versatility and fabulous image quality, at a price that's lower than those of its camera-brand competitors.

Tamron SP 15-30mm f/2.8 Di VC USD

This is a true rectilinear lens (well corrected for linear distortion), and boasts an expansive 110° field of view at 15mm. Mechanically and cosmetically, this is clearly a pro-calibre product. Since the front element protrudes, filters cannot be used but there's a built-in hood -- as well as eBAND and BBAR coatings -- to minimize the risk of flare. The optical formula includes an XGM Aspherical plus three pieces of Low Dispersion glass to minimize optical aberrations and distortion.

I often used f/2.8 while recording the vast, dark interiors of Gothic churches in Holland and my images exhibit outstanding sharpness even at the edges of the frame. At longer focal lengths, the central 70% was very sharp but for greater edge sharpness, it was worth stopping down to f/4 for superb results across the frame. Darkening at the corners (before correction with software, such as Silkypix that's included with this lens) is visible in images made at f/2.8 in the 15-20mm range, especially. By f/5.6 however, that's minimal. My best images made for excellent 16x24" custom prints with impressive definition of intricate detail.

The Bottom Line

Experienced photographers appreciate the advantages of a fast lens especially one with professional attributes in build and optics. If you fall into that category, or if you're a budding enthusiast who is ready for superior quality, check out these zooms at a nearby photo retailer. Though not inexpensive, they offer great value, with dividends that will definitely pay off.