Camera Accessories

One of the first Carl Zeiss lenses to go on sale for the Sony DSLRA100 camera, the 135mm F1.8 Sonnar T* is relatively large and heavy, with a massive front element. It's also extremely well-built, as you'd expect from a high-quality prime lens with a longish focal length. The T* designation indicates special multi-layer coatings on the lens elements to maximise light transmission and contrast. Claimed as the brightest telephoto lens in its class, it has nine aperture blades which close on a circular aperture, providing outstanding bokeh (out-of-focus blur).

The Sonnar design harks back to 1930 and derives its name from the German word "sonne", meaning sun, the symbol of ultimate brightness. Sonnar lenses have large maximum apertures and the design is frequently used for high-performance medium telephoto lenses with speeds up to f/2.8. Notable for their sharpness, they usually include special types of optical glass - in the case of the Sonnar T* 1.8/135 ZA, two Extra-low Dispersion (ED) elements. They also provide a high level of correction for common aberrations plus very even corner-to-corner illumination. This lens is an excellent example of the type.

Compatible with both the 'APS-C' sensor on the Sony DSLR-A100 camera and future DSLRs with 'full frame' imagers, the Sonnar T* 1.8/135 ZA sits comfortably on the A100 and provides a focal length equivalent to 202.5mm in 35mm format. Its weight is well balanced and the wide focusing ring moves smoothly and positively. Ridges on the ring provide a secure grip and the auto clutch prevents it from moving in AF mode. A distance scale is provided for manual focusing and depth-of-field indicators are included.

The view through the A100's viewfinder is very bright, thanks to the wide maximum aperture and this brightness carries through to images captured with the lens. Comfortably located on the left side of the lens barrel (when the lens is fitted on the camera) is a focus hold button that can be used to lock focus when you wish to measure exposures from off-centre areas in the field of view. Internal focusing allows the Sonnar T* 1.8/135 ZA to be used with angle-critical filters, such as polarisers and graduates. The supplied lens hood is very solid, simple to fit and effective. A neat protective pouch for carrying the lens is also provided.

Performance
Our tests involved both Imatest evaluation and field tests where we used the lens to record a number of different subjects. For the former, we compared the Sonnar T* 1.8/135 ZA with the Sony 75-300mm/F4.5-5.6 zoom lens that is offered in the A100 Twin Lens Kit.

Not unexpectedly, the Imatest MTF50 (resolution) results were lowest for the Sonnar T* 1.8/135 ZA at the widest apertures but improved rapidly to peak between f/4.5 and f/11. Performance remained above average all the way to the minimum aperture of f/22, although diffraction produced a measurable decline in resolution. There was also a very close correspondence between horizontal and vertical resolution, indicating superior imaging performance.

The Sony 75-300mm lens also turned in a surprisingly good performance for its specifications and price at the 135mm setting, especially considering the wide range of focal lengths the lens has been designed to cover. The best resolution came at f/8, with a gradual decline to f/22 and then a steep drop between f/22 and f/32, largely due to diffraction. The graph below shows how both lenses performed.


We recorded the lowest lateral chromatic aberration figures we've ever had with this lens (see below) and found it to be distortion-free. Edge-to-edge sharpness was also excellent and there was no sign of vignetting or unevenness in overall illumination.



In our field tests the major difference between pictures taken with the two lenses was the higher levels of brightness and colour saturation provided by the Carl Zeiss lens. In comparison, shots taken with the Sony 75-300mm lens looked rather subdued and much less 'punchy'. (You could probably adjust the zoom lens shots to look like the shots taken with the Carl Zeiss lens but they wouldn't be quite as sharp.)

Flare was well handled by both lenses but here again the Carl Zeiss lens had a competitive edge and out-of-focus areas were a little more attractively rendered. Autofocusing was very fast and very accurate, even in relatively low light levels, thanks largely to the speed of the lens. This also made the depth of field very shallow at f/1.8 - a fact that must be considered if you choose to use this lens for portraiture or close-ups.

SAMPLE IMAGES

Close-up performance is impressive.

The wide maximum aperture provides plenty of scope for selective focusing.

It also allows you to take shots of fast-moving subjects in dim lighting.

Flare is very well controlled and bokeh is particularly attractive.

 
This lens is great for candid shots with the A100 camera.

LENS PERFORMANCE COMPARISONS

Sonnar T* 1.8/135 ZA .

Sony 75-300mm/F4.5-5.6 zoom
Both the above shots were taken in heavy overcast conditions.

Sonnar T* 1.8/135 ZA

Sony 75-300mm/F4.5-5.6 zoom

Note the differences in contrast and colour saturation.

Maximum aperture: f/1.8

Minimum aperture: f/22
Lens construction: 11 elements in 9 groups

35mm focal length equivalent on A100 camera: 202.5mm

Angle of view (on A100): 12 degrees

Minimum focus: 0.72 m
Filter size: 77mm
Dimensions (Diameter x L): 88 x 114.5 mm
Weight: 985 grams