Sensor and Image Processing

The key feature of the three cameras is the three-layer Foveon sensor, which uses separate layers for recording red, green and blue wavelengths, eliminating the need for a low-pass filter and delivering images with richer colours. There’s been some controversy about how to specify the number of  pixels  in Foveon sensors; specifically whether to use the number of photosites or the total number of photodiodes as the megapixel count.

While Sigma lists the total sensor resolution of its DP Merrill cameras as 46 megapixels, it also indicates that each photosite contains stacked red, green, and blue colour sensing photodiodes as follows: 4,800 x 3,200 x 3. In effect, the DP Merrill cameras have the same number of photosites in the sensor array as a 15.4-megapixel camera and produce similar raw file sizes. (Imatest identifies the camera as having 14.8 megapixels.)

Because each photosite provides three data streams (red, green and blue), the sensor can deliver a higher spatial resolution than cameras with Bayer sensors of the same resolution. Sigma claims the new sensor can provide ‘luminance resolution equivalent to that of a 30MP CFA (colour filter array) sensor as measured on the standard B&W resolution chart used in conventional digital camera resolution testing’.

The sensor is partnered with a new Dual TRUE II image processing engine that was developed to handle the large quantity of image data produced by the sensor. The DP3 Merrill  is designed primarily for raw file capture and produces raw files in three sizes as well as offering JPEG capture in three sizes with three quality levels. The table below shows the options available with typical file sizes, all of which are recorded with the sensor’s 3:2 aspect ratio.

X3F.RAW files range in size from about 42MB   to more than 60MB, depending upon the amount of detail in the subject.   When they are converted into 8-bit TIFF files, the resulting files are around 45MB in size. This increases to about 85MB for 16-bit TIFF files.

Such large files place a burden on the image processor so it’s no surprise to discover the buffer memory can only hold seven high-resolution files, JPEG or raw.

Who’s it For?

To really enjoy this camera, you need to be an imaging geek. Sigma’s compact cameras and, specifically, their Foveon sensors, are not for everyday photographers who shoot JPEGs and want to record HD movies on the same device. You must be prepared to ‘work’ with the camera if you want it to work for you.

As a movie camera, the DP3 Merrill has little to offer. Like its siblings, it can only record video clips in VGA format but using a 3:2 aspect ratio that produces 640 x 426 pixel frames with a black bar along their lower edge.

This camera also takes a very long time to save files; and, although its autofocusing is generally accurate, it’s not lighting fast. While it is possible to take pictures of moving subjects and even hand-hold the camera with quite slow shutter speeds, this camera is best suited to photographing static subjects with low ISO settings. It delivers its best performance with X3F.RAW files.

(I don’t usually indulge in subjective reflections but I found the DP3 Merrill both exciting and enjoyable to work with. After a shooting session, I couldn’t wait to get home and check out the results on my computer. Many of the images were so sharp and rich in colour I simply had to print them – at A3+ size ““ and display them on the wall. It’s been a long time since any camera had that effect upon me.)

Build and Ergonomics

The DP3 Merrill has the   same ‘brick-with-a-lens-attached’ body as its siblings but the longest lens in the trio. (We haven’t reviewed either the DP1 Merrill and DP2 Merrill thus far.)

The corners and edged of the ‘brick’ are slightly rounded and smooth and the front panel carries three lines of dimples that form a finger grip. An irregular pentagon of the same dimples on the rear panel provides a thumb rest.

Measuring 121.5 x 66.7 x 80.6 mm and weighing roughly 440 grams when kitted out for shooting, it’s just small enough to slip into a jacket pocket. Its body is made from aluminium alloy and meets Sigma’s high construction standards.

The matte-black finish looks smart and professional and a number of small design features show attention to detail. However, the camera lacks both viewfinder and flash, although there’s a hot-shoe with a slip-off cover to protect the contacts for the optional EF-140 DG electronic flash. Although Sigma’s optional VF-21 viewfinder can be fitted, its coverage doesn’t match the camera’s 50mm lens.

The fixed 50mm, f/2.8 lens has an aluminium barrel to match the camera body. It takes up roughly half the space on the front of the camera and covers an angle of view equivalent to a 75mm lens on a 35mm camera. Its optical design contains 10 elements in eight groups and includes one SLD (Special Low Dispersion) glass element and one glass-moulded aspherical element.

A broad (35 mm wide) focusing ring surrounds the barrel making manual focusing easy and responsive. The supplied lens cap is relatively large and attached via a standard pinch clip. A cylindrical hood (LH3-01) is available as an optional accessory.

Roughly two thirds of the rear panel is taken over by the 3-inch TFT LCD monitor, which is fixed to the camera and has a resolution of 920,000 dots. It displays the full image captured by the sensor and its brightness is adjustable.

The remainder of the rear panel contains the main button controls, which include a conventional arrow pad plus buttons for accessing the AE-Lock/Delete, Quick Set, Menu, Playback and Display settings. The vertical buttons on the arrow pad   open sub-menus for the focus mode and AF point selection settings, while the horizontal buttons toggle through the exposure compensation settings.

Two buttons on the top panel are for switching power on and off and selecting the shooting mode. Only four shooting modes are supported for stills capture: Program AE (with Program Shift), Shutter-priority AE, Aperture-priority AE and Manual exposure. The sub-menu also displays an icon for the fully automatic Movie mode as well as three Custom memories for storing frequently-used combinations of shooting parameters.

Surrounding the shutter button is a large Command dial, which is used for adjusting selected settings. This dial and the shutter button sit proud of the top panel. There’s also a single (proprietary) USB/AV out port concealed below a lift-up cover on the right hand side panel.

The battery and memory card slot share a compartment in the base of the camera, while and the metal-lined tripod socket is located in line with the optical axis of the lens. Lugs for the neck strap are unobtrusive and lie close to the camera body.

Features

The DP Merrill trio have a number of features in common, aside from sensors and image processors. Their user interfaces are also the same and based upon those of previous Sigma cameras. Although distinctively ‘Sigma’ in styling, the control interface is quick and easy to use once you’ve worked out which buttons to press.

Most frequently-used functions are accessed by pressing the ‘Quick Set’ button on the rear panel. This opens a two-page menu, with each page covering four settings. The first page carries settings for ISO, metering, drive, and flash modes, while the second has the white balance, image quality/file format settings and the Colour Mode settings. You toggle between the pages by pressing the QS button and select the modes with the arrow pad and the settings within each mode by rotating the control dial.

The top button on the arrow pad is used to select the focusing modes, which include Macro, Portrait, Landscape/Snapshot and Custom settings. The last enables users to set a distance value from seven points between the closest focus and infinity.

Selection of the AF points is done by pressing the bottom button on the arrow pad. This displays the array of nine AF sensors. Pressing the Display button toggles between the 9-points select mode and the Free move mode, which lets you select individual sensors with the arrow pad buttons

Exposure compensation is adjusted with the horizontal buttons on the arrow pad. Most other functions are accessed by pressing the Menu button, which opens a menu containing four pages of Capture settings, two pages of Playback settings and four Camera settings pages.

Face detection AF is available as an option in the Capture Settings sub-menu, along with Speed-priority AF, which freezes the scene on the monitor while focusing is taking place.

Manual focus over-ride (by turning the focus ring on the lens) is available in the new AF+MF mode and the display is magnified by pressing the OK button when the focus position is close to correct. The closest focus is 22.6 cm in the Macro mode and users can choose between Spot, Regular and Large focus area frames.

Shutter speeds range from 30 seconds to 1/2000 second and flash synchronisation is available across the entire range as the camera has a leaf shutter within the lens. There’s no built-in stabilisation but the integrated lens-camera construction minimises vibrations produced by the shutter mechanism.

The DP3 Merrill’s menu provides eight Colour Mode settings: Standard, Vivid, Neutral, Portrait, Landscape, B&W, Sepia and FOV Classic Blue. The latter is designed to impart a rich blue tone to blue skies. Sigma provides no other information on this mode, which we found also boosted contrast and saturation slightly and added a yellow bias to orange and red hues.

Playback and Software

Nothing much has changed for image playback. You can toggle through the play options with the dedicated button below the arrow pad, which switches from image   plus basic data through image only to thumbnail plus comprehensive shooting data and four histograms (brightness plus R, G and B channels).

Playback zoom is available with up to 10x magnification and you can view ‘contact sheets’ of nine thumbnails at a time. The camera can also be set to display a ‘quick preview’ of each image immediately after it is taken and keep it on the screen for two (the default), five or 10 seconds. Other playback functions include locking/unlocking files, marking/unmarking files, slideshow playback and rotating and deleting selected files.

Movie playback is driven by the arrow pad buttons,   with the down arrow starting playback and the up arrow stopping it. The horizontal buttons control fast forward and rewind in 2x speed steps.

Unlike most cameras, the DP3 Merrill is not supplied with a software disk. The only application that can process X3F.RAW files from this camera is Sigma’s Photo Pro 5.5, which was released in February 2013 and is supplied as a download from the company’s website.

The application has been extensively revised since we last reviewed a Sigma camera. Its new user interface, shown below, is relatively straightforward and includes separate pages for file organisation, adjustment tools and the workspace.  However, it’s still relatively slow and lacks some of the adjustments found in Adobe Camera Raw.

Sigma Photo Pro 5.5 includes a monochrome mode, which is selected via a tab at the top of the adjustment tools panel. In this mode, you can create B&W pictures from the X3F.RAW files by accessing the  full RGB data for each pixel. The resulting images contain a wide dynamic range and high resolution.

Performance

When used with low ISO settings, the review camera delivered very impressive results. Subjective assessments of JPEG originals showed them to be sharp and detailed with rich and vibrant colours. Raw files converted into TIFF format with Sigma Photo Pro 5.5 were even sharper and more detailed and it was possible to make colours even richer without resorting to over-saturation.

Prints from these images were very impressive, confirming our subjective assessments of the camera’s potential for recording detail in raw files.

It was quite difficult to evaluate overall quality with our Imatest tests because the software ‘sees’ the files as having 14.8-megapixels (the size of the sensor array), rather than 46 megapixels (the number of individual colour detectors). This meant that even the lowest MTF50 figures from JPEG files came out well above expectations for the measured sensor resolution, while the best TIFF files were too highly resolved to measure.

Files were generally very clean and had little or no additional sharpening or other processing. However, colour charts were somewhat bizarre. Both JPEG and TIFF files showed boosted saturation for warm hues, with reduced saturation for   blues and greens. We don’t see this as a major issue because, even on the rare occasions when this was reflected in test shots, it was slight and easily corrected by simple editing.

Imatest showed the 50mm lens to be a superior performer, which maintained high resolution for both centre and edges of the field of view from f/2.8 to f/7.1, where diffraction began to take effect. Very slight edge softening was detected at apertures up to f/4.5.

Slight vignetting could be seen at the widest aperture settings. But it was never enough to affect image quality ““ or even be visible in most test shots. Flare and ghosting were seldom apparent unless the lens was forced to flare by including a bright light source in the frame. This produced some interesting colour artefacts, which could be partly corrected when raw files were processed.

Lateral chromatic aberration was negligible at all aperture settings, as shown in the graph below, in which the red line indicated the border between ‘negligible’ and ‘low’ CA. No coloured fringing was seen in test shots.

Despite claims that the sensor was not prone to moirø©, we found one instance of it occurring as a result of the tiled pattern on the Opera House shells. This pattern also showed up in monochrome shots of the same subject.

Imatest showed a steady decline in resolution as sensitivity was increased, with X3F.RAW files having a noticeable advantage over JPEGs at lower ISO settings, although both lost quality beyond ISO 1600.

In actual test shots in low light levels, the converted raw files contained richer colours than their equivalent JPEGs and were only slightly sharper at ISO 100. By ISO 800, the raw files were both sharper and had richer colours than their equivalent JPEGs.

Image noise was noticeable by around ISO 1600 and, although the raw files retained their colour advantage, both raw and JPEG files had begun to lose apparent sharpness. At ISO 3200 the JPEG files appeared very granular, while the raw files contained blotches of magenta, green and red. These effects were accentuated in both file types at ISO 6400.

Our timing tests were conducted with an 8GB SanDisk Extreme Pro SDHC UHS-1card. The review camera took just over three seconds to power up ready for shooting. We measured an average capture lag of 0.9 seconds which was reduced to 0.1 seconds with pre-focusing, indicating a sizeable AF lag. In low light levels it can take up to 2.5 seconds to find focus.

It took approximately eight seconds, on average, to process one high-resolution JPEG file; 17.8 seconds for each X3F.RAW file and 20.2 seconds for each RAW+JPEG pair. Shot-to-shot times averaged 2.2 seconds for both JPEGs and raw files. You can take another shot after the preceding one has been cleared, which means an enforced delay of about five seconds for JPEGs or 6.5 seconds for RAW+JPEG pairs.

In the continuous shooting mode the review camera recorded seven Large/Fine JPEGs in 1.5 seconds, which is close to specifications. It took 34.5 seconds to process this burst.

The buffer limit remained at seven frames  for both files and RAW+JPEG pairs and capture rates remained constant. However, processing times were extended to 46.5 seconds for raw files and 47.8 seconds for  RAW+JPEG pairs.

Video clips showed up the difficulties the camera’s processor has with certain colours. We filmed some close-ups of daisies that were deep russet red with bright yellow centres and found the colour of the petals had been pushed towards magenta.

Focus is set at the beginning of each clip but the camera appeared to be able to re-focus ““ albeit very slowly ““ when the camera was panned slowly from one part of the subject to another. Evidence of the rolling shutter effect could be seen in most pans. Sensitivity is set to auto in movie mode and the Quick Set button becomes inoperable.

Soundtracks were of average quality and we noticed no pick-up of camera sounds in the movie recordings. An 8GB   card can store up to 80 minutes of movie clips.

Conclusion

The DP3 Merrill is not for everybody. And, with a rated battery capacity of only 97 shots/charge,  it’s as well the camera is supplied with two rechargeable batteries, which are relatively quick to re-charge.

But if you’re after a compact camera with a ‘portrait’ focal length, and would be prepared to use low ISO settings and willing to record raw files and process them with Sigma’s software, the DP3 Merrill is capable of delivering superb results that can match – or better – the best DSLRs we’ve reviewed.

As the most specialised of the three DP Merrill cameras, it’s a very special camera for photographers with special requirements. There’s really no other camera that fits into the same niche. For this niche, it merits our Editor’s Choice award.

Buy

In summary

The DP3 Merrill is not for everybody. And, with a rated battery capacity of only 97 shots/charge,  it’s as well the camera is supplied with two rechargeable batteries, which are relatively quick to re-charge.

But if you’re after a compact camera with a ‘portrait’ focal length, and would be prepared to use low ISO settings and willing to record raw files and process them with Sigma’s software, the DP3 Merrill is capable of delivering superb results that can match ““ or better ““ the best DSLRs we’ve reviewed.

As the most specialised of the three DP Merrill cameras, it’s a very special camera for photographers with special requirements. There’s really no other camera that fits into the same niche. For this niche, it merits our Editor’s Choice award.

Rating

RRP:  AU$749; US$999