Camera Accessories

The Carl Zeiss Vario-Sonnar 24-70mm f/2.8 ZA SSM is a 'prestige' lens resulting from a collaboration between the well-known lens manufacturer, Carl Zeiss, and Sony. Made in Japan, it carries both Zeiss and Sony branding and has the model number SAL2470Z. Its focal length range of the covers an angle-of-view range equivalent to 36-105mm in 35mm format with 'APS-C' sized sensor on the A350 body we used for this review.

Constructed from 17 elements arranged in 13 groups, it includes two aspheric elements and two Extra-low Dispersion (ED) elements to minimise chromatic aberration and rectilinear distortion. Carl Zeiss's T* coating on optical surfaces ensures higher light transmission and, at the same time, reduces flare and ghosting.

The f/2.8 maximum aperture is retained throughout the zoom range and a nine-bladed, circular iris enables photographers to control background blur. This feature makes the lens ideal for portraiture, particularly when the lens is fitted to one of the current Sony Alpha bodies. We'll have to wait to see whether it will be equally successful on a full-frame DSLR.

For its focal length range, the Vario-Sonnar 24-70mm f/2.8 ZA SSM is a large and heavy lens, adding almost a kilogram to the overall weight of the camera (when the lens cap and hood are taken into account). However, it's also very robustly built and elegantly designed.

As with most zoom lenses, the focusing ring is towards the front, while the zoom ring is closer to the camera body. Between them is a distance scale with feet and metre markings at 0.34, 0.4, 0.5, 0.7, 1, 2 and 5 metres plus infinity for manual focusing.  Both the zoom and focusing rings have narrowly-ridged rubber coatings that provide a secure grip, although we found they tended to trap grit. They are relatively wide, with the zoom ring slightly wider than the focusing ring.

Adjacent to the distance scale is a focus mode switch for shifting between auto and manual focusing. (This is used in conjunction with the manual focus switch on the camera body.) A central focus hold button locks focus in AF mode. No depth of field or infrared indicators are provided on the lens barrel.

The lens is supplied with a padded carrying pouch, which has a solid circular base and drawstring closure. It's a rather tight fit when you insert or remove the lens (especially if the lens hood is reversed over the lens barrel) but provides excellent protection. The lens cap, which carries both the Zeiss logo and a discrete Alpha symbol, fits with standard spring clips that are large enough to grip easily when the lens hood is in position. Packaged with the lens is a slip of paper carrying the name of the staff member who inspected the lens before it left the factory; a reassuring touch.

Handling
The review lens fitted very snugly onto the A350 body we used for our tests, with a positive click-in fit. Its weight made it feel slightly out-of-balance on the A350 and we feel it would be more at home on the larger A700 model - and even better on the future 'full frame' DSLR cameras, which Sony promises to begin releasing during this year.
Zooming from the 24mm to the 70mm position required roughly a quarter of a turn. The zooming movement, although rather tight, was very smooth and quiet. No zoom lock is provided and the lens showed no tendency to 'creep' when the camera was held facing downwards.

Moving from the closest focus to infinity required just over a third of a turn, making accurate manual focusing easy. Focusing movements were very smooth and we found no evidence of the 'plastic-on-plastic' sensation we found with the 16-80mm lens. The SSM (Super Sonic wave Motor) was almost silent and autofocusing was both fast and accurate.

Performance
Imatest testing showed the supplied lens to be a very good performer and a good match to the A350's high resolution. The best resolution was obtained between f/4.0 and f/7.1 with the 24mm, 35mm and 50mm settings, while the 70mm setting produced its highest resolution between f/6.3 and f/9.0. Imatest showed a fair amount of edge softening at wider apertures, with the 70mm focal length setting being less affected than wider angles of view.

At smaller apertures, performance tailed off gradually but remained well above average and the differences between centre and edge resolution became less. The graph below plots the centre resolution from our Imatest tests against lens aperture and focal length.

Lateral chromatic aberration was negligible with the 50mm and 70mm focal length settings and only ventured into the 'low' level at the wider focal lengths. At no focal length setting would it be enough to affect normal photographs. A graph plotting the CA values against the focal length setting - with the red line marking the border between 'insignificant' and 'low' - is provided below.

Vignetting (edge darkening) was negligible at all apertures and focal length settings. Rectilinear distortion was barely detectable. Bokeh (out-of-focus blur) was very smooth and attractive, as shown in the sample image below.

 
70mm focal length, 1/320 second at f/4.0

Flare was reasonably well contained in most backlit shots, although we found a series of bright flare patterns in several shots taken with the lens pointing towards the sun (but without the solar disk in the frame). The circular shape of these flare spots reflects the circular shape of the lens iris.

24mm focal length, 1/250 second at f/11

SAMPLE IMAGES

24mm focal length, 1/50 second at f/18

70mm focal length, 1/50 at f/18

24mm focal length, 1/15 second at f/9

26mm focal length, 1/15 second at f/16

50mm focal length, 1/125 second at f/5.6

Focal length range: 24-70mm (equivalent to 36-105mm with APS-C sensor)
Picture angle: 84 degrees to 34 degrees (61-23 degrees with APS-C sensor)
Maximum aperture: f/2.8 throughout zoom range
Minimum aperture: f/22
Lens construction: 17 elements in 13 groups (includes two aspheric elements and two ED elements)
Lens mount: Sony Alpha mount
Diaphragm Blades: 9 (circular iris)
Minimum focus: 34 cm
Filter size:  77mm
Dimensions (Diameter x L): 83 x 111 mm
Weight: 955 grams