Sigma dp1 Quattro Review

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dp1 Quattro
Specifications
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Basic Specifications
Full model name:	Sigma dp1 Quattro
Resolution:	19.61 Megapixels
Sensor size:	APS-C (23.5mm x 15.7mm)
Lens:	Non-Zoom (28mm eq.)
Viewfinder:	No / LCD
Native ISO:	100 - 6400
Extended ISO:	100 - 6400
Shutter:	1/2000 - 30 sec
Max Aperture:	2.8
Dimensions:	6.4 x 2.6 x 3.4 in. (161 x 67 x 87 mm)
Weight:	15.0 oz (425 g)
Availability:	10/2014
Manufacturer:	Sigma
Full specs:	Sigma dp1 Quattro specifications

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Sigma dp1 Quattro

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19.61 Megapixels	Non-Zoom	APS-C size sensor

Sigma dp1 Quattro Review -- First Impressions

by Mike Tomkins
Preview posted 02/10/2014

At the 2006 Photokina tradeshow, Japanese third-party lens manufacturer Sigma announced development of its first compact digital camera. A year and a half later, the Sigma DP1 -- the camera that started the trend for large-sensor, fixed-lens compacts -- hit the market. Although there have been many followups in the six years since, they've all shared that one most important hallmark of Sigma's camera line: the Foveon X3 image sensor. (Sigma went on to acquire Foveon in November 2008.)

A radical change. But now, the status quo has gone out the window. With the Sigma dp1 Quattro and its simultaneously-launched siblings, the dp2 Quattro and dp3 Quattro -- the company uses a brand-new image sensor that's fundamentally different to those of its forebears. It's still a Foveon chip, and in fact still carries X3 branding, but the Foveon X3 Quattro image sensor is a huge departure from the sensors which have preceded it.

Before we go any further, a recap of the Foveon X3 sensor would probably be appropriate. Since it's only ever been used in Sigma's SD-series DSLRs and DP-series fixed-lens cameras, one quickly-discontinued, Polaroid-branded small-sensor compact camera, and a variety of industrial / scientific cameras, the X3 sensor line has likely flown under many photographers' radars. It has a pretty devoted following from a small subset of the photographic community, however, who've shunned more established name-brands in favor of Sigma's cameras.

How the others do it. Traditional CMOS and CCD image sensors can't differentiate between the wavelengths of light being collected by their photodiodes. Instead, they use a color filter over the surface of the sensor to reject most of the light before it reaches the photodiode, permitting only a limited range of frequencies to be gathered. That color filter array -- most typically a 2x2 pixel Bayer array with two green, one red, and one blue pixel that's repeated across the sensor surface -- allows color data to be recreated for the image.

Unfortunately, it also greatly reduces light-gathering efficiency, and reduces resolution -- especially color resolution. For any given pixel location, two thirds of the color information must be interpolated (read: guessed) by looking at the values of surrounding pixel locations. This can result in color moiré and false color artifacts. The process of demosaicing to recreate the final image requires battery-sucking processor power. Alternate color filter arrays such as RGBW, and Fuji's EXR / X-Trans exist and can mitigate some of these issues, but in turn can be even more computationally intensive.

Foveon 1.0. Foveon's X3 sensor works in a completely different manner, taking advantage of the fact that light of different wavelengths will penetrate to different depths in the silicon from which the sensor is constructed. Photodiodes aren't just spread across the sensor surface, but also stacked vertically. The result is that the sensor can record full color information at every pixel location -- there's no demosaicing to do, color moiré and false color are avoided, and no valuable light is turned away by a color filter array.

There's no free breakfast, though. Foveon sensors have had issues with cross-contamination of colors between channels, higher noise levels (especially color noise) and limited ISO sensitivity, drastically reduced saturation at higher sensitivities, reduced dynamic range, and modest performance (since they must read and process three times as much data for any given pixel count, compared to a Bayer camera). And although they are resistant to color moiré and false color, they can still suffer from luminance moiré, albeit at higher frequencies.

Still full color? The Foveon X3 Quattro aims to deal with some of these issues. The manner in which they're addressed is at once interesting, and quite a departure from the way in which they've worked in the past, something that may cause concern for Foveon-faithful fans. The reason? Although technically full color information is still being gathered at every pixel location, a variance in the pixel size and pitch between the top layer and those below it means that, if you count the resolution of the top layer as that of the camera, the layers beneath have significantly lower color resolution.

The top layer, which responds most strongly in the blue channel, has an effective 19.6 million photodiodes. Both layers beneath have just 4.9 million photodiodes, however. That brings up the potential for color moiré and false color artifacts, the very thing Foveon sensors have until now managed to avoid.

Forget the concept of megapixels. Ever since we first heard of the X3 Quattro chip, we've been debating precisely how to describe it on our site. Foveon's chips have always defied categorization in terms of the not-so-humble megapixel, but more than ever that's true with the Quattro image sensor.

In the past, we've always reported a resolution of one-third that claimed by Foveon and Sigma, who both count every photodiode as contributing to the megapixel number. Neither approach has felt entirely fair, though. Taking the example of the flagship Sigma SD1 digital SLR, its manufacturer would count it as a 44 megapixel design in terms of output images, where we classify it as 14.8 megapixel. In truth, its performance lies somewhere in the middle -- resolution of the SD1 is similar to that we'd expect from a 25-30 megapixel camera.

But now, things have taken an even more complex turn. Sigma and Foveon still add the number of photodiodes from all three layers. In their opinion, the sensor in the Sigma dp1 Quattro is a 29.4-effective megapixel chip, a number they round down to 29 megapixels. Given that it no longer has identical pixel grids on all three layers, it feels more unfair than ever to simply divide this by three, and call this a 9.8-megapixel camera. At the same time, though, referring to a camera that has only 4.9-megapixel resolution on two of its three color channels as being a 29-megapixel camera seems just as far from the truth.

We now have, essentially, no meaningful way to describe this sensor or the cameras on which it is based in terms of pixel resolution. You'll see it described at the top of this page as a 19.6 megapixel sensor, but realistically until we get it into the lab, we have no idea how it will correspond to a typical, Bayer-filtered camera in terms of pure resolution. It could, conceivably, still better a 19.6-megapixel Bayer chip in terms of luminance resolution, or it could go the other way.

So why the change? Reducing the resolution of two out of three layers so radically, however, bring some advantages. For one thing, there's now a whole lot less information to read off the sensor and process for every shot. That should translate to greater performance -- although Sigma has yet to provide any spec for burst shooting speed.

Also, with larger photodiodes for the lower layers, noise levels should be reduced in two out of three channels. (Specifically, the red and green channels.) And although color resolution will certainly be reduced compared to a standard Foveon X3 chip of equal pixel count, luminance resolution will hopefully suffer less, with much of the information able to be reconstructed from the higher-resolution top layer.

Of course, this is all theory so far. Suffice to say, we're keen to get a Foveon X3 Quattro-based camera into our labs to see how it performs in the real world.

But enough sensor talk. There's a new camera here, too -- well, three of them, actually. And we're going to go on record as saying that the new body they share is going to prove just as controversial as the sensor that lies inside them. To call this body design radical would be to downplay just how unusual it is.

Walkaround. Where most cameras are either relatively box-like, or have a handgrip of some kind projecting from the front, perhaps accompanied by a smaller thumbgrip on the rear, the Sigma dp1 Quattro takes a different route. There's a small projection on the front, angled outward about 20 degrees, and finished in a sharp 90-degree corner around which your fingers will grip. On the rear, there's a much larger projection on which is control pad and focus button. This, too, finishes at a fairly sharp edge that then angles back towards the camera body and curves to meet it. The control pad, however, sticks out of the side of this angled surface.

Jumping to the front of the unusually wide dp1 Quattro camera body for a moment, it's almost entirely smooth and featureless, save for the angled grip, lens, a two-hole microphone port at the far left end (as seen from the rear), and a small leatherette grip pad at the base of the grip. Unusually, the autofocus assist lamp can be found not in the camera body, but in the top right corner of the lens barrel. We do have concerns about the width in terms of handling comfort, incidentally, because it shifts the center of gravity a long way out from the already quite controversial handgrip. This is a camera you'll be shooting two-handed, we're fairly certain, if for no other reason than to reduce wrist strain.

A fair few controls are to be found on the unusual, reverse L-shaped top deck. Sitting right of the flash hot shoe -- and note that there's no built-in flash at all -- you'll find the Power button, a Mode button, and two flat-topped dials, neither of them ergonomically angled. The shutter button sits inside the front dial. A sensor plane mark at the far left end of the body shows just how close to its front the sensor sits, just a tiny fraction behind the rear of the lens barrel. One remaining control -- the manual focus ring -- sits around that barrel.

On the rear, once you get past that grip, the remainder of the dp1 Quattro's back panel is relatively flat, accommodated only by the 3.0-inch, 920K-dot LCD monitor and a handful of controls. One of these -- the Play button -- sits snug between the leatherette rear surface and the cover plate that tops the LCD. The others -- Display mode, Quick Set, AE-lock / Delete, and Menu -- sit in a column just a little further right. The SD card access lamp sits at the very bottom left corner, adjacent to the SD card slot and USB port, which live under a small door on the left end of the body.

On the bottom, you'll find a battery compartment door with dummy battery cable cutout in the base of the unusual grip, and a small projection for the tripod mount beneath the lens. While some tripod mounting plates may not prove ideal with the arrangement, it does look to place the tripod socket not only on the central axis of the lens, but also very close to the focal plane as well, which has advantages for panorama shooters.

The difference is in the lens. The key difference between the Sigma dp1 Quattro and its siblings, the dp1 Quattro and dp3 Quattro, can be found in their lens. The Sigma dp1 Quattro is based around a 19mm f/2.8 prime lens, equivalent to a 28mm lens after taking into account the focal length crop of the APS-C sized X3 Quattro imager's 23.5 x 15.7mm surface area. Both of the dp1 Quattro's siblings also have f/2.8 prime optics, but that of the dp2 Quattro is a 30mm (45mm equivalent) lens, while the dp3 Quattro has a 50mm (75mm equivalent) optic.

The Sigma dp1 Quattro's lens has nine elements in eight groups, and a nine-bladed iris aperture. Focusing is possible to as close as 20 centimeters, and maximum magnification is 1:8.3. With lens, the dp1 Quattro has a body depth of 3.4 inches. Weight hasn't yet been disclosed.

Processor. Handling output from the new image sensor, there's also a brand-new TRUE III image processor. We don't yet have any information as to how much of a performance improvement it brings.

Autofocus. The dp1 Quattro uses a nine-point contrast-detection autofocus system. Three AF point sizes are available, and the focus point can also be moved freely around the frame. Face detection is provided, as is a focus lock function.

Sensitivity. The Sigma dp1 Quattro offers sensitivities ranging from ISO 100 to 6400 equivalents in 1/3 EV steps. The whole range is available under automatic control, courtesy of configurable high and low limits.

Exposure. There are a choice of just four exposure modes in the dp1 Quattro, just the way experienced shooters like it-- Program, Aperture-priority, Shutter-priority, and Manual.

Exposures are determined using evaluative, center-weighted average or spot metering, and +/-3.0 EV of exposure compensation is available in 1/3 EV increments. There's also a three-stop auto-bracketing function within the same range. An AE lock function is available.

Shutter speeds vary from 1/2,000 to 30 seconds, although the entire range may not be available depending on your chosen aperture, suggesting that the iris itself is used to time the exposure.

Creative. Among the dp1 Quattro's creative options are a choice of 11 color modes and 10 white balance modes, with the latter including Color Temperature, Flash, and Custom modes.

Connectivity. The Sigma dp1 Quattro's connectivity options couldn't be much simpler -- USB data (presumably 2.0 High Speed), and a cable release switch.

Power. The dp1 Quattro draws power from a BP-51 lithium-ion rechargeable battery pack. Battery life is rated at 200 shots on a charge. Two batteries as well as a dedicated battery charger are included in the bundle.

Price and availability. The Sigma dp1 Quattro ships from mid-October 2014, at a list price of about US$1,000.