Review based on a production SD1 with firmware 1.05, and a production SD1 Merrill with firmware 1.0
Note: Most of the material in this review was prepared using the 'original' SD1 rather than the 'Merrill' model. Sigma assures us that the two cameras are identical in all practical respects, and we've verified this in key areas of image quality, speed and operability using an SD1 Merrill. Because of this, we consider this review to apply equally to both models. In the text we've used 'SD1' to refer to both cameras for the sake of brevity.
The SD1 created a huge amount of interest when it was announced at Photokina 2010. Having used Foveon's original 4.7x3MP sensor in its SD and DP series of cameras, Sigma bought the sensor company in 2008 and instructed it to focus its efforts on high quality stills photography. The result was a 15x3MP sensor of the standard APS-C size (approx. 24 x 16mm, slightly larger than Foveon's previous designs), and it's around this that the SD1 is built.
The SD1's original pricing caused a great deal of dismay; at an RRP close to that of the professional full-frame Nikon D3X and Canon EOS-1Ds Mark III SLRs, it was placed at a level most Sigma users found entirely unattainable. However almost a year on, after what we'd assume must have been disappointing sales, Sigma relaunched the camera as the 'SD1 Merrill' with a dramatically-reduced price tag.
The SD1 Merrill still isn't cheap, though, in fact it's one of the most expensive APS-C SLRs on the market. But at a price of around £1800 / € 2100 / $2300, at least it's now in the same ball park as top end models like the Canon EOS 7D and Nikon D300s. As such, it's graduated from being a distinctly niche product to one that many more professional and enthusiast photographers might plausibly consider buying.
The SD1 is a camera with a solid specification, though not one that particularly stands out in the enthusiast-grade DSLR sector. In terms of size and body design, metering and autofocus systems, and external controls, it's most comparable to the likes of the Canon EOS 7D, Pentax K-5, Nikon D7000 and Sony SLT-A77. What it doesn't offer, though, are two features that have become standard over the past few years - movie mode and live view. We suspect that the omission of video capability may not lose it too many buyers amongst its target market, but for a high-resolution camera that would seem particularly suited to studio work, the lack of live view (and the critical focusing and composition it allows) could be a deal-breaker.
The other potential hurdle for the SD1 is its use of Sigma's own SA lens mount. The company builds a wide range of lenses for the mount, and many of them are very good indeed. But we ask ourselves how many people will be willing to risk spending money building up a collection of lenses for a non-mainstream mount. It's also worth noting that few of Sigma's lenses offer any form of weather sealing to match the camera body.
Foveon sensor
Obviously the Sigma's defining feature is its 15x3MP Foveon sensor. For those of you who haven't come across the technology before, it uses a fundamentally different method for detecting color than any other camera sensor. Almost all other cameras place a pattern of colored filters in front of their sensors so that each individual photo site is only receives either red, green or blue light. To create a full-color pixel in the final image, clever mathematics is applied to estimate the values of the two unmeasured colors, based on the amount of those colors captured by adjacent photos sites.
Foveon's technology doesn't use filters - instead it uses the fact that different colors of light can penetrate silicon to differing extents. Foveon's chip measures the number of photons captured at three different depths corresponding to how well Red, Green and Blue can penetrate the chip. The main advantage of this is that, unlike other digital cameras, the Sigma measures all three colors at every one of its 15 million photo sites, capturing three times as much color data per-pixel as a conventional sensor. (Hence the company's reference to it being a 46MP camera.)
Because the Foveon sensor captures full color data at each pixel location, it's not susceptible to color moiré - false color patterns that are the result of those clever calculations occasionally getting things wrong, for example with finely-woven fabrics. Traditional Bayer-pattern sensors suppress this by using an optical low pass (or anti-aliasing) filter that slightly blurs the image at the pixel level, reducing the camera's resolution. The Foveon sensor doesn't use an AA filter, and is therefore able to resolve substantially more detail than its pixel count alone might suggest - in principle the SD1 has the potential to produce resolution similar to a 30MP Bayer-type sensor.
Sigma SD1 specification highlights
15x3MP Foveon X3 CMOS sensor
ISO 100-6400
11-point AF sensor (all cross-type)
5 frames per second continuous shooting
460,000 dot LCD screen
Shutter capable of 1/8000th second and rated for 100,000 cycles
Per-lens AF fine tuning
Sigma SD1 vs SD1 Merrill - what's the difference?
Sigma says the SD1 Merrill is functionally identical to the SD1, and our experience with the two cameras supports this entirely. The only visible differences between them are that the new model has 'Merrill' written on the back of the camera and on the baseplate serial number sticker. They also require different firmware files with different version numbers, but we suspect that this is purely to accommodate the change in model name within the EXIF data.
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