Andy Westlake tests Sigma’s unconventional SA-mount mirrorless camera, the sd Quattro
Sigma sd Quattro review: Features
The sd Quattro’s most important feature is its Foveon X3 Quattro image sensor. Unlike conventional sensors, which use a pattern of red, green and blue-coloured filters over their light-sensitive photodiodes to determine colour, it’s based around the fact that the different colours of light can penetrate silicon to different depths. It has a top layer with 19.6 million pixels that’s most sensitive to blue light, with two layers beneath that each use 4.9 million pixels four times in area, and that are sensitive to green and red light. Because of this arrangement, Sigma calls it a 29.5-million-pixel sensor.
This unique approach means that its X3F raw files can only be processed using Sigma Photo Pro (SPP). Unfortunately, this is one of the slowest and least intuitive pieces of software I’ve ever used, and it’s a serious weakness of the entire system. It’s capable of delivering good results, but you’ll need a fast, up-to-date computer and the patience of a saint.
On paper, the sd Quattro looks like a reasonably well-equipped camera. Its output resolution is 19.6 million pixels, although the unusual design of the Foveon sensor promises to capture finer detail and colour gradation compared to a conventional Bayer sensor with a similar pixel count. The sensitivity range covers a decidedly modest ISO 100-6,400, and files can be captured in the 14-bit losslessly compressed X3F raw format. These can now be converted to JPEGs in-camera after shooting, with plenty of control over processing parameters such as brightness and white balance.
Shutter speeds range from 1/4000sec to 30secs, with a bulb option and 1/180sec flash sync speed. Continuous shooting is available at 3.6fps with a 12-frame raw buffer, and files are recorded to a single SD card. In keeping with the camera’s market positioning, only the four key exposure modes – program, aperture priority, shutter priority and manual – are on offer.
As is usual for mirrorless cameras, both autofocus and metering employ the main imaging sensor. According to Sigma, AF uses a hybrid system with both phase detection and contrast detection on board; users can either select from a nine-point mode, or move the focus area freely across a space roughly 75% of the height and width of the frame. The focus area can also be changed in size in three steps, including a fine point for focusing on a precise part of the scene. Face detection is also available.
One unusual addition is Sigma’s new SFD mode, standing for ‘super fine detail’. While this superficially resembles the high-resolution modes found in recent Pentax and Olympus models by shooting a series of exposures and combining them into a single raw file, here it brackets seven shots at 1-stop increments. In essence, this makes it a high dynamic range mode, designed to record extra detail in the shadows and highlights for post-processing. I’ll look into how well it works later.
Other features are notable by their absence. There’s no built-in flash: you can use either a hotshoe-mounted unit or employ the PC sync port on the front plate. Unusually for a modern camera, the sd Quattro has no video mode, and Wi-Fi connectivity is missing too, although support for Eye-Fi cards is included.