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We've been waiting for Sigma's DP-1 digital camera for approximately 18 months. First announced at Photokina in September 2006, it has been withheld from the market through what Sigma describes as "unforeseen image quality problems which resulted in a requirement to change the specification of the camera's imaging pipeline". But it's here now - and a very interesting camera it has turned out to be.

The DP-1's metal camera body is sturdy with an angular styling and clean lines that are reminiscent of Ricoh's GR Digital models.  Although the dimpled areas on the front and rear panels are well positioned, we'd have liked a slightly better grip. A small moulded protrusion would have provided greater comfort and (perhaps) allowed a few more components to be packed into the camera. Unfortunately, the plastic lens cap supplied with the review camera didn't match its build quality and couldn't be used when the lens hood was in place.

One of the most impressive features of this camera is just how much Sigma has packed into its compact body. The sensor is between five and seven times larger than the sensors used in other digicams, which would put the DP-1 in a class of its own were it not for the fact that it's also a very special type of imager (see below).

Not surprisingly, the lens on the DP-1 is substantially larger than the lenses on most digicams. The 16.6mm prime lens has a focal length is equivalent to 28mm in 35mm format.  It extends almost two centimetres from the camera body when power is off and more than doubles its length when the camera is turned on. Its aperture range of f/4-f/11 is not particularly fast but appears to be a good match for the DP-1's sensor.

No optical zooming is possible but the camera has buttons for a digital zoom function that applies up to 3x magnification. Manual focusing is provided via a dial that is inset into the top rear panel just behind the shutter button. It's very well positioned, turns easily without any click-stops and is easy to use for fast manual focusing.

 
The on-screen display for manual focusing, showing the distance indicator and selected AF point.

The 2.5-inch LCD screen is non-adjustable and covers roughly half of the rear panel. Its 230,000-pixel resolution is half the resolution of the display on the new Ricoh R8 camera and lacks its clarity.  We found the screen on the review camera to be quite susceptible to fingermarks, requiring regular cleaning. The camera itself has no viewfinder but the optional VF-11 accessory finder is reasonably bright and easy to use. 

An on/off button, mode dial and shutter release button are the only controls on the top panel. The mode dial carries auto, P, A, S and M shooting modes plus settings for video and audio capture. No scene modes are provided (this is definitely not a camera for point-and-shoot photographers). The mode dial is well positioned and you're unlikely to set the wrong mode accidentally.

Just above the LCD on the left side of the rear panel is a slider switch that raises the pop-up flash. This tiny flash is pretty feeble, with a guide number of 6 (ISO 100/m), which makes it about half as powerful as most digicams' flashes. (See Performance below for the results of our flash tests.) An accessory flash (EF-1400G) with a GN of 14 is available when more power is needed and is 2.3 times brighter than the built-in flash.

Right of the LCD are buttons for the AE lock, exposure compensation/delete, wide/tele zoom controls and an arrow pad with a central Menu/OK button. The top button on the arrow pad doubles as a focus mode controller, while the bottom button controls flash modes. Below the arrow pad are quick review and display buttons.

The metal tripod socket is centrally located on the optical axis on the bottom panel. A sliding plastic cover beside it lifts to reveal the battery and memory card compartment. This cover fits snugly when it's shut. Two small metal strap loops are located at the top of the side panels for the neck strap supplied with the camera. A lift-up rubber cap covers the USB and video-out ports.

The DP-1 with HA-11 lens hood and VF-11 viewfinder fitted and the pop-up flash raised.

Although the camera only comes with battery and charger, neck strap, cables, instruction manual and software CD, the review camera was supplied with the three main accessories that are available as options: the VF-11 optical viewfinder (RRP $189), the HA-11 lens hood (RRP $29.95) and the EF-1400G flash (RRP $129). The flash requires two AAA batteries (not supplied). Both the viewfinder and the flash fit snugly onto the camera's hot shoe, so you can't use them together.

The Sigma DP-1's video capture capabilities look pretty ordinary when compared with other recent digicams. But we were surprised to find the Foveon sensor could record video at all. QVGA resolution is supported, although the user manual claims the actual image area per frame is 320 x 212 pixels. However, frames can be recorded at 30 frames/second and clips are stored as AVI files (with sound). You can record up to 30 minutes of video on a 1GB memory card.

The maximum amount of video data that can be recorded in one movie shoot is 2GB and recording will be terminated when this point is reached. Recording also stops when battery power runs low. While clips are being recorded, the camera displays both available recording and elapsed times on the LCD. 

Sensor
The DP-1 differs from all other digicams in two respects, both related to its image sensor. For starters, its sensor is roughly seven times larger in area than the sensors in similarly-sized digicams. Secondly, it's a Foveon imager chip, which captures colours in three layers in a manner similar to film. The diagram below shows how the chip's structure differs from other digital sensors but resembles the structure of film.

 
Source: Foveon.

The Foveon sensor takes advantage of the fact that red, green, and blue light penetrate silicon to different depths. Image data can, therefore, 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.

In the DP-1's  specifications Sigma lists its sensor as having '14.06 million output pixels (2652 x 1768 pixels x 3 layers)'. It appears to be the same imager as (or very similar to) the chip used in the company's SD14 DSLR, although the image data is handled differently in the DP-1. There's no Super High JPEG setting and the results we obtained from the DP-1 were quite different from those we obtained from the SD14 (see Performance below).

The surface area of each photosite is approximately 7.8 microns, which is considerably larger than any digicam on the market and larger than the photosites on many DSLRs. We believe it also has a new microlens overlay. The larger sensor has several advantages over small sensor digicams that also support high resolution. For starters, it can record a much wider dynamic range. It also captures more image data and, therefore, more pictorial information.

The illustrations below show the differences between the DP-1 and the Ricoh R8 (which has a 10-megapixel sensor that measures 6.16 x 4.62 mm).

The photograph above of an outdoor concert in very contrasty lighting originated as an X3F.RAW file taken with the DP-1. Compare it with the shot below of the same subject, taken with the Ricoh R8, noting the greater dynamic range in the DP-1 shot (clouds are visible in the sky and detail is recorded in the awning over the stage). More details is also recorded in the grass in front of the stage in the DP-1 and the colours are more natural-looking.

Enlargements (below) show more detail was recorded in the shot taken with the DP-1 than in the shot from the R8. Edges are also sharper. The advantages of the larger photosites on the DP-1 are clearly shown in these shots.

An enlarged version of the photograph taken with the Sigma DP-1 above.

A similar enlargement of the photograph taken with the Ricoh R8 shows how much more detail is captured in the raw file from the DP-1.

Image Processing
Coupled to the imager chip is Sigma's TRUE (Three-layer Responsive Ultimate Engine) image processor, which has been designed specifically for the Foveon chip and claims to provide high-speed image processing. The maximum image size the camera can produce is actually 2640 x 1768 pixels - and that's what you get when shooting JPEGs. This equates to 4.67 megapixels, which is pretty small for a modern digicam - and a deterrent against using this camera to shoot JPEGs.

In its shooting menu, the DP-1 supports four JPEG sizes: Hi (2640 x 1768 pixels), Wide 16:9 (2640 x 1485 pixels), Med (1872 x 11248 pixels) and Low (1312 x 880 pixels). You can only record raw files at the camera's default 3:2 aspect ratio.  

Four Image Quality settings are provided for JPEGs: Fine, Norm, Basic and Raw. RAW + JPEG shooting is not supported but raw files contain a JPEG, which is extracted for monitor playback. Typical in-camera image file sizes are shown in the table below.

Interestingly, when you convert the X3F.RAW files to TIFF format, you end up with a 4573 x 3048 pixel image, which equates to 13.94 megapixels. So Sigma's claim of 14-megapixel resolution for the DP-1 is valid. Obviously, the conversion involves pixel-interpolation to increase the image size. (It took 5.47 seconds to process each X3F.RAW file with the supplied Sigma Photo Pro software.)

Menus
Pressing the central button on the arrow pad opens the DP-1's menu system, which has two sections: shooting and setup. There are 15 pages in the shooting menu, some of which are shown below. Essentially, the DP-1 provides the same options as a typical digicam, although with the addition of raw file capture and the ability to select between the standard sRGB colour space and Adobe RGB. In-camera adjustments are provided for contrast, sharpness and saturation, with +/- one EV in 1/3EV steps for each parameter.

The setup menu is somewhat more extensive that most digicams provide, with 17 items covering the standard date/time, language, preview/review, LCD brightness and contrast, auto power off, format, key sound, video and USB connection settings. It also provides an easy way to access the firmware settings and updating.

We'd like to have seen a more user-friendly menu design as the DP-1's menus can be difficult to read in bright lighting. We'd also like to have had a Function menu, similar to that in the SD14 for quicker access to frequently-used settings like ISO, exposure compensation and white balance.

Using manual focusing is also somewhat hampered by the size of the on-screen icons and the general difficulties associated with the LCD display. The same difficulties are found when adjusting brightness contrast and sharpness settings in the camera. There's a lot of unused real estate on the screen that could be better allocated to larger, more easily read icons.

Playback
Playback capabilities are fairly basic and include single image (with basic shooting data above and below the frame or as a thumbnail with shooting data plus a brightness histogram), playback zoom with a magnification up to 10x, nine-shot index viewing, playback of images with sound and a rudimentary slideshow option. 

Playback with shooting data.

Playback with data plus histogram.

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. The DP-1 does not support automatic rotation of vertical shots but users can rotate selected images for display on the LCD.

The slideshow function lets users show all files or a selection consisting of all marked or locked files. 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 video playback.

Software
The DP-1 is supplied with the latest version of Sigma Photo Pro (v2.4 for Windows, v3.1 for Mac), which is currently the only raw file converter that can open X3F.RAW files from this camera. Its user interface is almost identical to the version supplied with the SD14. This application combines a fairly average file browser with a better-than-average raw file converter.

The browser interface of Sigma Photo Pro.

You can choose to view only the JPEGs or X3F raw files or have both displayed together, along with TIFF files that have been created from the raw images. You can also rotate, mark and lock selected images when you want to identify or protect shots you really want to keep.

The software also contains a magnifying loupe for inspecting images and you can display highlight and shadow alerts. Facilities are also provided for renaming individual shots and batch renaming as well as selecting one or multiple images. You can also open multiple review windows to compare selected shots.

Double-clicking on an image opens the file in the editor/raw converter, which provides three adjustment modes: X3F (for raw files), Auto and Custom. With X3F selected each image is displayed as it was captured by the camera. Moving the selector to Auto automatically adjusts the shot while Custom allows you to make your own adjustments by clicking on the Adjustment Controls tag at the upper right corner of the pane.

The Adjustment Mode window contains sliders covering exposure, contrast, shadow and highlight detail, saturation, sharpness and an X3 Fill Light setting. Groups of settings can be saved for subsequent use on other raw shots. A colour wheel is provided for tweaking image colour and an eyedropper lets you display RGB values for any point in the image or neutralize the hue of a neutral colour with a colour cast. There's also a small RGB histogram and adjustments to set the shadow and highlight values for the warning masks (which can be turned on and off via a checkmark box).

The conversion interface showing the white balance adjustment window.

To adjust white balance settings, you must use the dropdown menu in the Edit section on the toolbar. The settings provided replicate the settings provided in the camera but provide no further adjustments. The custom setting is replaced by an Original setting which restores image colours to the 'as shot' values. The Monochrome setting in this menu is non-destructive and you can restore colour and adjust white balance after processing an X3F file to create a B&W image.

Clicking on Save Image As opens a window that allows you to select the source images, adjustments modes, processing settings (output image size, colour space, file type and JPEG quality) and the destination folder. There's also a button on the main window that lets you replace the stored settings in an X3F file with adjusted values.
Sigma Photo Pro 2.4 also provides an Image Info window for viewing image metadata. It's accessed by clicking on either a thumbnail in the browser or an image in the review window. The Image Information Window remains open and floats above the Main and Review Windows until you close it, or until you exit the program.  You can copy the metadata from this window to the clipboard for pasting into word processors or similar applications.

Performance
The stand-out feature of the DP-1 is its ability to record a much wider dynamic range that any digicam we've reviewed - and also than many DSLRs. Although both JPEG and X3F.RAW files looked rather flat when viewed on both the camera's LCD and our computer screen, it was possible to obtain very good results from the test camera - but only when we worked with raw files.

The apparent 'flatness' of the DP-1's image files also showed up in Imatest testing, where both JPEGs and converted raw files showed significantly lower saturation levels than we've seen in the past. This isn't a problem for photographers who shoot raw files with this camera. It's usually better to have converted TIFF files with low contrast and saturation as a basis for subsequent editing. You can easily boost both parameters without reducing image quality.

We obtained very good results by converting images in Sigma Photo Pro 2.4 and only making minor adjustments in the raw file processing interface.  Subsequent levels adjustments and tweaks to contrast and saturation could then be done when the converted 16-bit TIFF files were opened in Photoshop. This enabled us to obtain accurate colours and a similar depth of colour to the SD14 files.

Resolution remained high throughout the test camera's ISO range, with a slight decline - that was greater with JPEG files than X3F.RAW files - at the higher ISO settings. The graph below shows our test results.

The test camera's lens showed slight edge softening in our Imatest tests but delivered consistently high resolution throughout its aperture range and excellent sharpness in shots. The graph below plots the results of our Imatest tests.

Lateral chromatic aberration was consistently low and we found no evidence of coloured fringing in test shots. The auto white balance setting on the test camera had the usual problems with incandescent lighting but delivered an almost neutral colour balance with fluorescent lighting. The presets tended towards slight over-correction but the manual measurement system produced neutral results with both types of lighting.

Low-light prformance was mediocre, with a severe loss of colour in long exposures shot as JPEG files. Raw fiels fared only a little better.The built-in flash was too weak to illuminate an average-sized room at any of the camera's ISO settings. However, the EF-1400G accessory flash produced enough light at ISO 200 and above.

Although the test camera powered-up in just over a second and the shutter was quite responsive, autofocus lag was a significant issue, particularly in dim lighting. We measured an average capture lag of one second, which reduced to 0.1 seconds with pre-focusing.

It took 2.5 seconds to process and store a JPEG file and just over two seconds to store a raw file. In continuous shooting mode the DP-1 can only capture bursts of three shots, regardless of the file format. JPEG frames were recorded at intervals of approximately 0.2 seconds, while X3F.RAW files were slightly slower at intervals of just under 0.3 seconds. It took just under nine seconds to process and store a burst of three large/fine JPEGs and seven seconds to process and store a burst of three raw files.  

Conclusion
Sigma's DP-1 is a revolutionary camera - and quite different from any other digital camera in the current marketplace. This, in part, accounts for its relatively high price tag and restricted feature set (prime lens, pared-down set of controls, limited video capabilities). It is not a camera for point-and-shoot photographers. Nor will it suit photographers who only shoot JPEGs and prefer not to become involved in subsequent editing.
But, if you are prepared to shoot raw files, convert them into 16-bit TIFF with the slightly quirky Sigma Photo Pro software and then work on them in a sophisticated image editor, the rewards are there in the form of images with an excellent dynamic range and rich, natural-looking colours.

We hope the DP-1 will be the first in a rapidly-increasing category of compact digital cameras with large-area sensors that will include cameras from other DSLR manufacturers. (Amateur Photographer in the UK has reported that the DP-2 and DP-3 are 'coming', one of them possibly with a zoom lens. There has also been speculation that one may have a 40mm f/2.0 prime lens.  We'll probably have to wait for Photokina for confirmation.)

As a pioneer in a technically challenging arena, Sigma has done a great job with this camera by packing so much into such a small body. In the DP-1 it has produced a fascinating imaging tool that has potential to develop a cult following. Although it's not the ideal solution to a serious photographer's compact camera requirements, the DP-1 is a great start - and a credit to its manufacturer.

Image sensor: 20.7 x 13.8 mm Foveon X3 Direct Image Sensor (CMOS) with 14.06 million output pixels (2652 x 1768 pixels x 3 layers)
Lens: Sigma 16.6mm f/4-f/11 lens (28mm in 35mm format)
Zoom ratio:  approx. 3x digital
Image formats: Stills - X3F.RAW (12-bit lossless compression), JPEG (Exif 2.21); Movie AVI/WAV
Image Sizes: 2640 x 1768, 2640 x 1485, 1872 x 11248, 1312 x 880
Shutter speed range: 15-1/2000 second
Image Stabilisation: n.a.
Exposure Compensation: +/- 3EV in 1/3 EV steps
Focus system/range: Contrast detection AF with 9 AF points; range 30 cm to infinity; manual focus available
Exposure metering/control: 8-segment TTL  full aperture metering; evaluative, centre-weighted average; Auto, P, A, S, M shooting modes
ISO range: Auto (ISO 100-200), ISO 100, 200, 400, 800
White balance: Auto, Sunlight, Shade, Overcast, Incandescent, Fluorescent, Flash, Custom
Flash GN/modes/range (ISO auto): GN 6 (ISO 100/m), Forced flash, Red-eye reduction, Slow synchro; range – 30 cm to 2.1 m (ISO 200)
Sequence shooting:  3 frames in approximately 0.7 seconds
Storage Media: SD and SDHC cards
Viewfinder: Optional accessory
LCD monitor: 2.5-inch TFT colour LCD (230,000 pixels)
Power supply:  BP-31 lithium-ion rechargeable battery (approx, 250 shots/charge)
Dimensions (wxhxd): 113.3 x 59.5 x 50.3 mm
Weight: 250 grams (without battery and card)