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Although many photo enthusiasts have been looking forward to Sigma's DP2 since the camera was first revealed at Photokina 2008, we've had to wait almost eight months to see a review unit. Physically and technologically similar to the original DP1 model (which Photo Review reviewed in March 2008), the DP2 comes with a standard-range lens that is considered more suitable for snapshots and portraits.

Like the DP1 (which continues in Sigmas's line-up, the DP2's lens has a fixed focal length. However, instead of being wide-angle, it offers a 24.2mm focal length that equates to 41mm in 35mm format. You can't zoom in with this lens - either optically or digitally. The only zooming provided on the DP2 is playback zoom (up to 10x), whereas the DP1 provided buttons for a 3x digital zoom function (which wasn't particularly useful).

Constructed from seven elements in six groups, this lens is substantially faster than the DP1's lens, covering an aperture range from a wide f/2.8 to f/14. Its aperture range is, therefore, significantly wider than most digicams, which typically stop at f/8.


Front view of the Sigma DP2 with the lens extended. (Source: Sigma.)

The body of the new model is otherwise identical to its predecessor, as is the Foveon image sensor, which appears to be used in all cameras - both compact and DSLR - in Sigma's very limited range (only three models released so far). Naturally, the lens on the new model is a bit larger, although not as much as you might expect. It extends approximately 46 mm from the camera body when the camera is powered up but only 24 mm when power is off (compared with 19mm for the DP1's lens).

What's New?
Apart from the lens, Sigma has implemented a few small - but significant - changes in the DP2. Some are improvements over the DP1; others aren't. One of the best is the re-design of the mode dial, which sees the elimination of the full-auto mode (which no photographer who buys this camera would want) and the addition of Set-up access via the mode dial.

Top view of the Sigma DP2 with the lens extended, showing the redesigned mode dial. (Source: Sigma.)

Unfortunately, photographers shifting from the DP1 to the DP2 will need to accommodate to a number of changes, and the black-on-black labels on the buttons (carried over from the DP1) don't make this easy. The AE lock button is still there, but it now doubles as the delete button. Below it is a new Quick Set button that accesses two sub-menus, each covering four functions. Hitting the QS button toggles between them and each display is colour-coded for easier identification.


Rear view of the DP2 showing the white balance menu displayed on the LCD.

The first (QS1) adjusts flash, ISO, metering pattern and white balance settings, allocating each sub-menu to one button on the arrow pad. The second (QS2) covers image quality, image size, drive mode and colour mode.


Settings accessed via the QS1 interface.


Settings accessed via the QS2 interface.

The colour modes expand the colour settings in the menu on the DP1 to include seven 'style' processing modes: Standard, Vivid, Neutral, Portrait, Landscape, B&W and Sepia, all pretty self-explanatory. Sigma has also added a new Picture Settings function that enables users to adjust contrast, sharpness and saturation in images across five steps up or down.


Colour mode settings.

Both Picture Settings and colour mode adjustments are locked into JPEG files but recorded in the metadata in raw files and can be re-set when raw files are converted in the supplied software. They can also be applied to untagged raw files during the raw conversion process.

Some settings are restricted in different shooting modes. The highest ISO settings (ISO 1600 and ISO 3200) can only be used when recording raw files which, themselves, can only be captured at 2640 x 1760 pixels (no 'small' raw file option exists). B&W and Sepia colour modes are not usable for raw file capture. Embedded JPEG previews can be extracted from X3F.RAW files by some image browsers.

Sigma has also endeavoured to clarify its main menu system by introducing two menu interfaces: List Display and Open Display. List Display is the same as the original DP1 menu. Open Display expands each parameter selection to show the options available. You toggle from one parameter to the next via the digital zoom and playback buttons.


The List Display menu mode.


The Open Display menu mode.

Having moved most of the frequently-used settings to the Quick Set button, the main menu is used primarily for setting up the camera for parameters like preview times, bracketing order, Picture Settings, auto rotation and custom button allocations. It's still difficult to read, particularly in bright outdoor lighting, and the low resolution of the screen doesn't help this situation.

Interestingly, you can only set the white balance manually for JPEG shots via the Capture Settings section of the main menu. This will annoy some potential buyers since all other WB pre-sets can be selected through QS1. If you're shooting raw files this shouldn't be an issue as you can correct colour casts when you convert the files into editable formats (JPEG or TIFF).

The DP2 offers a fair amount of interface customisation and pre-set combinations of functions can be saved for later use.  You can allocate functions like program shift, exposure compensation, shutter speed and aperture value to the horizontal arrow pad keys, digital zoom and playback buttons for each shooting mode. You can also re-set the AE lock button to include both AEL and AFL or just Centre AF lock. You can also decide whether to make half-pressing the shutter double as an AE lock.


The Load My Settings interface that underpins the ability to customise most operations in the DP2.

What's Not
The monitor on the DP2 is a big disappointment for such a highly-priced camera. If Canon can install a 3-inch, 461,000-dot LCD on its $649 (RRP) Ixus 990 IS and PowerShot G10 (RRP $799) models, surely Sigma could do something similar on the $1199 DP2. A higher-resolution screen could also make that almost unusable menu system easier to read.

The lack of an AF-assist lamp is also frustrating as, like the DP1, the DP2 is slow to focus in low light levels. In fact, overall autofocusing is noticeably slower than most digicams whatever the light level. (Fortunately, manual focusing is straightforward and quite effective, although the focus limit of 28 cm restricts the usefulness of this camera for close-up work.)

There's still no decent grip on the camera body. All you get are dimpled areas on the front and rear panels and, although they are well positioned, they aren't as comfortable or secure as we'd like. The plastic lens cap supplied with the camera remains pretty rough-and-ready.

The battery for the DP2 is the same BP-31 lithium-ion rechargeable battery as used in the DP1. Its claimed capacity of 250 shot/charge is more like that of entry-to-mid-level digicams than a sophisticated semi-professional camera. 

Sensor and Image Processing
We've covered the Foveon sensor used in the DP2 pretty thoroughly in our review of the DP1. Measuring 20.7 x 13.8mm, it's roughly 12 times larger than the '2.5-inch' type (5.76 x 4.29 mm) sensors found in most digicams. This factor alone means the light-capturing photodiodes are also larger, boasting a pixel pitch of 7.8 microns.


A comparison of the size of the Sigma DP-series Direct Image Sensor with a typical digicam sensor. (Source: Sigma.)

This chip takes advantage of the fact that red, green, and blue light penetrate silicon to different depths, enabling image data to be extracted at three levels, corresponding with the blue, green and red channels that make up a digital image.

No filtration is required to record colour information and no colour interpolation when the image data is processed. Colours should, therefore, be more accurately and richly recorded with a Foveon chip. We found this to be the case with raw files from the DP1, although JPEGs from that camera looked rather flat.

Since reviewing the DP1, Photo Review has discovered how Sigma has managed to fit such a large sensor into a small camera body. The main engineering issue camera manufacturers must deal with when designing camera bodies for larger sensors is heat. Larger sensors not only generate more heat but also require larger lenses, which require more energy to drive, further increasing operating temperatures.

DSLR bodies provide more opportunities for installing heat sinks to cope with the heat produced by the AF motors and image sensors and some AF motors are located in the lens, rather than the camera body. However, in small slim cameras, all the components are packed in so tightly it's difficult to find any unused space.

In the DP1 - and also the DP2 - the metal front panel of the camera body becomes a heat sink for the sensor and focusing motors. It's a novel approach that has proved successful over time, although the camera becomes warm (but not hot) to the touch when you take a series of shots in a relatively short time.

With the DP2, Sigma has released a new image processing engine, known as the 'TrueII'. According to the company, it has been developed to 'do full justice' to the Foveon X3 sensor's 'uniquely sophisticated 3-D rendering power'. It is also supposed to improve in-camera image processing quality and speed and enhance colour reproduction and dynamic range. (Photo Review didn't notice significant improvements in any of these factors in the course of our tests.)

The DP2 offers the same image size and quality settings as the DP1, with four JPEG sizes: Hi (2640 x 1760 pixels), Wide 16:9 (2640 x 1485 pixels), Med (1872 x 1248 pixels) and Low (1312 x 880 pixels). Raw images are captured in 12-bit X3F.RAW format. Unfortunately, RAW+JPEG capture is not supported. This may be because the TRUEII processor can't handle the extraction of JPEG images from the X3F.RAW files at point of capture.

Unlike the DP1, when you convert the X3F.RAW files to TIFF format, you end up with a 2640 x 1760 pixel image, which equates to 4.65 megapixels (although the software has an option that allows you to create double-sized TIFF files). Image files are, however, the same size in each camera. So Sigma's claim of 14.06-megapixel effective resolution must be based on pixel-interpolation across the three colour-sensitive layers in the chip to increase the image size. 

As in the DP1, movie clips can only be recorded with QVGA (320 x 240) resolution at a frame rate of 30 fps. Quality is as you would expect and similar to clips from the DP1. Roughly 30 minutes of video can be recorded on a 1GB SD card. Users can also add 10- or 30-second voice clips to still images via the voice recording function.  

Playback and Software
Playback modes are fairly basic and include single image (without shooting data, with basic shooting data above and below the frame or as a thumbnail with shooting data plus a small RGB histogram). An over-exposure warning can also be set up in the playback menu.


The histogram plus image data playback display.

Playback zoom enables magnification of images up to 10x. Pressing the lower of the 'zoom' buttons lets you toggle between the nine-frame index view and Jump mode which lets you browse 'pages' of thumbnails via the arrow pad. Shots can be locked to prevent accidental deletion or deleted individually.

Individual shots can also be 'marked' as favourites, for inclusion in slideshows or for group deletion. Both locking and marking can be reversed in the playback menu. Unlike the DP1, the DP2 supports automatic rotation of vertical shots, although this function can be disabled in the main menu.

You can also display images as a slideshow and select all files on the card or only those marked or locked. The time each image appears on the screen can be set to two, five or 10 seconds and you can have the slideshow stop at the end of the sequence or loop to provide a continuous display.

When movie clips are played back, the first frame of the selected clip is displayed as a still picture. Pressing the bottom button on the arrow pad starts movie playback and also pauses playback. The horizontal buttons are used for fast forward and reverse, while the top button stops playback. Playback of sound recordings uses similar controls to the movie playback.

The supplied Sigma Photo Pro software (v. 3.5 for Windows; 3.3 for Macintosh) is the only application provided. It can also be downloaded from Sigma's DP2 website (http://www.sigma-dp.com/DP2/photopro.html). Despite being an update on the application supplied with the DP1, the user interface and capabilities of this file browser and raw file converter are largely unchanged. We covered them extensively in our review of the DP1 but we've included some screen shots here to show readers some of its capabilities.


The browser window of Sigma Photo Pro v. 3.5 for Windows.


The editing window for X3F raw files.


Saving options for converting raw files into TIFF or JPEG format.


Tracking progress when an image is saved.

Performance
Not surprisingly, many aspects of the DP2 were the same as (or very similar to) the DP1. Like the DP1, the new model is not designed for point-and-shoot photographers but for photographers who are prepared to spend a fair amount of time adjusting camera settings before shooting - and also on their computers processing the image files afterwards.

Sigma has made some welcome improvements to the quality of the JPEG files in the new model, although they still look a little flat. Correctly-exposed raw files maintain the depth and potential we found in files from the DP1. The dynamic range in outdoor shots from the test camera appeared to be less than in similar shots from the DP1 and great care had to be taken to avoid even slight over-exposure as highlight clipping was an ever-present issue with both JPEGs and raw files.

We're not sure whether this issue related to the sensor or the image processing system, since we didn't find it to this degree in the DP1.  We suspect the latter as it was present with all metering modes - although more common with evaluative metering. Maybe the in-camera conversion algorithms also play a role.

In Photo Review's user tests, the DP2 proved as sluggish to use as the DP1. Autofocusing was relatively slow on the review camera and also quite noisy, with a low growl emitted each time the camera lens was adjusted.
Focusing also tended to be unpredictable. Although reasonably competent in bright conditions, in poor lighting - particularly with complex subjects that included near and far elements - the AF system often failed to find focus where you wanted it. Focusing manually was the only effective option at such times.

The battery supplied with the review camera, which we charged before commencing our tests, was depleted after only 83 shots in our initial series of tests. However a second charging resulted in more than double this capacity - although, at 196 shots, it was still a little short of the claimed 250 shots.

Interpreting our Imatest tests on raw files was tricky because, unlike the DP1, where the converted raw files showed up as 4528 x 2993-pixel (13.6-megapixel) images, converted raw files from the DP2 were shown as having 2640 x 1760-pixels (4.65-megapixel). This makes it difficult to compare the two cameras - and also to compare the DP2 with other cameras because there were many files for which the Imatest results were in excess of the identified resolution of the sensor.

Suffice it to say that X3F raw files converted into 16-bit TIFF files produced higher resolution than the highest-resolution JPEGs. This difference was lowest at ISO 800, the highest sensitivity available for JPEG files. Resolution was noticeably reduced in raw files taken at ISO 3200. The graph below shows the results of our Imatest tests.

The test camera's lens also appeared to have a 'sweet spot' between f/3.5 and f/6.3, although with raw files, resolution was significantly higher at smaller lens apertures than it was for JPEG files taken with the same aperture settings. The graph below shows the results of our Imatest tests.

Imatest showed most hues to be slightly (but not seriously) off the mark. Colour saturation was relatively low for yellows and oranges but slightly high for reds and blues. Skin tones were shifted slightly towards warmer values. These shifts are correctable when raw files are converted into editable formats with the supplied software.

Lateral chromatic aberration was effectively negligible at all lens apertures and we found no evidence of coloured fringing in test shots from the supplied camera. The graph below shows the results of our Imatest tests.

Low-light performance was only marginally better than we found with the DP1, with a severe loss of colour in long exposures that was reflected in both JPEG and raw files. Noise and colour shifts became increasingly obvious from ISO 400 on and 15-second exposures shot at ISO 800 were almost unusable.

The built-in flash was too weak to illuminate an average-sized room at ISO settings lower than 400. However, flash exposures at high ISO settings showed none of the colour shifts we observed in the long exposures and contained much less image noise.

Distortion was negligible in the lens on the review camera and vignetting was barely visible. Edge and corner sharpness were excellent and bokeh was acceptable for the focal length of the lens and sensor area. Contre-jour shots were often slightly flare-affected but overall performance was good with backlit subjects.

White balance performance was similar to most digicams we have reviewed. The auto setting failed to totally remove the green cast produced by fluorescent lighting and shots taken under incandescent lighting retained s noticeable orange cast. The manual pre-sets over-corrected slightly with both lighting types but the custom setting, although tricky to use, produced close-to-natural colours.

For our timing tests we used a 4GB Class 6 SDHC memory card to maximize the camera's capabilities. For both JPEG and raw files in the P shooting mode we measured a constant average capture lag of 1.2 seconds, which reduced to 0.3 seconds with pre-focusing. Each JPEG image took an average time of 2.2 seconds to process, while it took almost five seconds to process each raw file.

In the continuous shooting mode the review camera was able to record four high-resolution JPEG images in 1.1 seconds. Processing appears to be on-the-fly as it took only 2.3 seconds to process this burst. For raw files, the buffer limit was three files and the buffer memory filled in 0.8 seconds. It took 10.2 seconds to process this burst.

Buy this camera if:
- You're looking for a well-built pocketable camera with P, A, S and M shooting modes - and can afford the relatively high price tag.
- You're prepared to shoot and process raw files.
- You don't mind working with a frustratingly non-intuitive user interface and menus that are difficult to read outdoors.
- You're happy to use the monitor for shot composition.

Don't buy this camera if:
- You want a point-and-shoot digicam.
- You require high-quality images in dim or contrasty lighting - and when shooting under incandescent lights.
- You want to shoot widescreen or high-definition video (the DP2 can't). 

IMATEST GRAPHS

From unedited JPEG files.

From X3F.RAW files converted into 16-bit TIFF format with Sigma Photo Pro software without additional adjustments.

SAMPLE IMAGES

Auto white balance with incandescent lighting.

Auto white balance with fluorescent lighting.

ISO 100; 15-second exposure at f/3.5.

ISO 3200; 15-second exposure at f/14; X3F.RAW file converted into 16-bit TIFF format with Sigma Photo Pro software and then into JPEG format with Photoshop CS4.

ISO 100; 1/3 second at f/2.8; X3F.RAW file converted into 8-bit TIFF format with Sigma Photo Pro software and then into JPEG format with Photoshop CS4.

ISO 3200; 1/60 second at f/3.2; X3F.RAW file converted into 8-bit TIFF format with Sigma Photo Pro software and then into JPEG format with Photoshop CS4.

JPEG image original; ISO 100; 1/400 second at f/9.

The same image after adjustment in Photoshop CS4


X3F.RAW file converted into 16-bit TIFF format with Sigma Photo Pro software and then into JPEG format with Photoshop CS4. ISO 100; 1/400 second at f/9.

JPEG original; 1/400 second at f/9; ISO 100.

X3F.RAW file converted into JPEG format with Sigma Photo Pro software. ISO 100; 1/640 second at f/10.

Crop from corner of the above image, enlarged to 100%,

Backlighting; X3F.RAW file converted into 8-bit TIFF format with Sigma Photo Pro software and then into JPEG format with Photoshop CS4. ISO 100; 1/320 second at f/8.

Contre-jour lighting; ISO 100, 1/160 second at f/7.1.

An example of blown highlights in a converted raw file; ISO 100, 1/100 second at f/5.6.

Skin tones from an X3F.RAW file converted into 8-bit TIFF format with Sigma Photo Pro software with some adjustment to correct colour shifts; ISO 100, 1/80 second at f/3.5.

 X3F.RAW file converted into 16-bit TIFF format with Sigma Photo Pro software and then into JPEG format with Photoshop CS4. ISO 100 1/30 second at f/7.1.

X3F.RAW file converted into 16-bit TIFF format with Sigma Photo Pro software and then into JPEG format with Photoshop CS4. ISO 100 1/640 second at f/2.8.

Image sensor: 20.7 x 13.8 mm Foveon X3 Direct Image Sensor (CMOS) with 14.06 megapixels effective  (2652 x 1768 x 3 layers)
Lens:  24.2mm f/2.8-f/14 (35mm equivalent focal length: 41mm); 7 elements in 6 groups
Zoom ratio: n.a.
Image formats: X3F lossless compression RAW data (12-bit), JPEG (Fine, normal, basic), Movie (AVI) Voice memo to still image (10 sec), Voice recording (WAV)
Image Sizes: Stills - 2540 x 1760, 2640 x 1485, 1872 x 1248, 1312 x 880; Movies – QVGA (320 x 240) at 30 fps
Shutter speed range: 15 to 1/2000 second
Self-timer: 2 or 10 second delay
Image Stabilisation: n.a.
Exposure Compensation: +/- 3EV in 1/3EV steps
Focus system/range: Contrast Detection Type; range – 28 cm to infinity  ; dial type manual focus
Exposure metering/control: TTL Full Aperture Metering with Evaluative, Centre-weighted Average  and Spot Metering
Shooting modes: Program AE, Shutter Priority AE, Aperture Priority AE, Manual
ISO range: AUTO (ISO 100-ISO 200); With Flash (ISO 100-ISO 400); ISO 50, 100, 200, 400, 800, 1600
White balance: Auto, Sunlight, Shade, Overcast, Incandescent, Fluorescent, Flash, Custom
Flash modes/range (ISO auto): Pop-up (Manual) with auto exposure control; GN 6
Sequence shooting:  Just under three frames/second for 3 raw or 4 JPEG frames
Storage Media: SD/SDHC/MMC cards
Viewfinder: n.a.
LCD monitor: 2.5-inch TFT Colour LCD with 230,000 dots
Power supply:  BP-31 rechargeable lithium-ion battery (approx 250 shots/charge)
Dimensions (wxhxd): 113.3 x 59.5 x 56.06 mm
Weight: 260 grams