The 24.6-megapixel Alpha A900 is Sony's first full-frame digital SLR and is aimed at professional photographers, especially studio-based pros looking for the ultimate in high resolution.
At the heart of the A900 is Sony’s Exmor sensor, scant details of which were made public at the start of the year. It’s a full-frame CMOS chip, with a total count of 25.7MP and an effective output of 24.6MP, and it contains over 6,000 parallel analogue to digital (A/D) converters. This, Sony claims, allows data to be converted quickly to resist noise and other interference, with noise reduction applied on-chip both before and after the signal has been converted. The sensor has been designed to match the capabilities of Sony’s Alpha range of lenses, in particular its G series and those manufacturers under the Carl Zeiss brand.
Images from the camera measure 6048 x 4032 pixels at their maximum resolution, with an average JPEG weighing in at just under 70MB when opened. In addition to the three levels of JPEG compression, the camera supports Raw and compressed Raw (cRaw) formats; this latter setting reduces files by around a third in size, with a supposedly negligible effect on image quality. So much so, in fact, that Sony’s intention is to make it the primary Raw recording option in its future models.
The sensor’s design has also taken into account the image-stabilising Super SteadyShot function. It follows the same sensor-shift principle we’ve seen before, though the system has been redesigned to cater for the larger surface area of the sensor. This makes it the first full-frame image-stabilisation system, claimed to offer up to four steps of usable shutter speeds slower than would be otherwise possible. In comparison with Sony’s previous Super SteadyShot systems, it’s also claimed to be 1.5x more powerful and able to function 1.3x faster, with the vibrating mechanism also serving to combat the effects of dust.
The camera offers a standard sensitivity range of ISO 200-3200, expandable to equivalent settings of ISO 100 and 6400. Noise reduction is optional for exposures longer than a second, while images shot at or above ISO 1600 carry additional options for high, normal or low noise reduction. Driving this and all other operating and processing functions is a take on the Bionz processing technology we’ve seen before. Notably the camera now contains two processors, which apply further dual-step noise-reducing algorithms as part of their image processing. The processor also allows for a sustained burst rate of 5fps at the full 24.6MP resolution, for up to 105 Fine JPEG files or 12 Raw files, or 10 Raw+JPEG files at either full or compressed Raw settings.
As with Nikon’s D700 and D3 models, the A900 offers support for both ‘full-frame’ and Sony’s DT range of lenses, the latter specifically designed for cropped sensors. Any mounted DT optic decreases the effective resolution to 11MP while increasing the focal length magnification factor to 1.5x, though Sony has made it clear that it cannot guarantee exposure when DT lenses are used in certain situations. The reason for this is that the edges of the lens sit inside the sensor’s full-frame area, obscuring the peripheries which can influence metering.
Predictably, we see some features carried on from the A700, and the metering pattern is one of these; this comprises a 40-segment honeycomb pattern and both average and spot options. Dynamic Range Optimisation has also been included, with Standard and Auto Advanced settings, in addition to a further advanced option that allows you to fine-tune optimisation to one of five levels. Meanwhile, the focusing module sports nine standard points and 10 AF assist points, with its central point being the only one of the dual-axis ‘cross’ variety. This is said to enhance accuracy when shooting at apertures of f/2.8 or wider.
The area where Sony has made considerable noise is the A900’s pentaprism viewfinder. The aim was to surpass the performance of the Minolta Dynax 9, and not only does Sony claim to have achieved this, but to have bettered the performance of its competitors, too. Figures provided by Sony claim that the finder exhibits a 0.2 – 0.4EV brightness advantage over competing models, and 20% less distortion than the Dynax 9. This is aided by Sony having redesigned the condenser lens at the prism’s base and the eyepiece optics, while multi-layered, anti-reflective coatings have been applied to help minimise ghosting. What results is a viewfinder with an approximate coverage of 100% and a magnification factor of 0.74x.
Sony’s approach to live view has been a curious one, in that it has developed the most efficient and fluid version we’ve yet seen but only included it on two of its DSLRs. The live view-less A700 was released at a time when every other manufacturer was pushing the technology, and once again the A900 does the same – the logic behind this being that live view isn’t as great a priority as other features. Had its current live view system been implemented in the a900 this would have compromised the performance of the viewfinder (given the extra sensor in the camera’s prism), so essentially we have that impressive viewfinder in its place.
Just as impressive is the camera’s body. Sony has said that making the A900 lightweight was one of its objectives, and at a body-only weight of 850g it’s done well to fulfil this aim. Looking at the camera’s construction, a frame consisting of aluminium has been complemented with magnesium alloy panels around the front, back and top, while a polycarbonate mirror box has been reinforced with carbon fibres. The mirror unit itself has also seen a revised construction, using a ‘parallel-link’ mechanism to adjust the angle at which the mirror is lifted. By doing so, the mirror lifts over two pivots rather than swinging from one, and, given its size, it’s able to travel more efficiently.
One of the more interesting features we see debuting in the Alpha range is the Intelligent Preview function; this allows you to take a preview image, before varying exposure, dynamic range and white balance settings and seeing their effects upon the image. Four small histograms – one for each colour channel and one for exposure – are provided alongside, and once the desired settings have been selected the camera then sets these for you to take the final image. In fairness, this isn’t the first time we’ve seen such a concept, though how comprehensive it is sets it apart from other implementations.
Flash and Battery
There’s no built-in flash, though compatible units include Sony’s innovative HVL-58AM, which features a Quick Shift Bounce system ideal for portrait-oriented shooting. Thanks to its rotating head it provides the same concentration of light whether the camera is held in either a portrait or landscape orientation, and is even capable of adjusting its own white balance. Other units include the cheaper HVL-F42AM flashgun, ring and twin-light options, and third-party units from Sigma, Metz and Sunpak.
Finally, the camera’s InfoLithium battery is claimed to offer up to 880 shots from a single charge, with its charged percentage constantly displayed on the camera’s LCD screen. Considering that the camera has two processors to deal with this is quite an achievement, though the lack of both live view and a video facility helps conserve power.