A well-built DSLR camera for photographers who want to work with raw files to obtain maximum image quality.It’s taken a while for Sigma’s SD15 to reach the market. First displayed at Photokina 2008 and then officially announced as a successor to the SD14 on 20 February, 2010, the SD15 has only just gone on sale locally. It offers a few updates to its predecessor but features the same Foveon X3 sensor, which has a focal length crop factor of 1.7x. . . [more]
It’s taken a while for Sigma’s SD15 to reach the market. First displayed at Photokina 2008 and then officially announced as a successor to the SD14 on 20 February, 2010, the SD15 has only just gone on sale locally. It offers a few updates to its predecessor but features the same Foveon X3 sensor, which has a focal length crop factor of 1.7x.
One of these updates has been to improve the quality of JPEG files from the camera although, like its predecessors, the SD15 has been designed for raw file capture. And the real strength of the Foveon sensor is only revealed in X3F.RAW files (see Sensor and Image Processing below).
Build and Ergonomics
Nothing much has changed since we reviewed the SD14 back in March 2007. The new model’s body dimensions are the same as its predecessor’s and, although it weighs 20 grams less, it’s just as ruggedly constructed. The shutter mechanism is rated for 100,000 exposures, typical of professional cameras.
If you like a solid and substantial camera, the SD15 is very comfortable to hold and use and its ergonomics are generally well designed. Although some controls are in different places from other manufacturers’ cameras and the user interface is quirky (to say the least), once you’re familiar with the camera you’ll find using it soon becomes intuitive.
Front view of the Sigma SD15 with the 17-70mm lens. (Source: Sigma.)
The front panel hasn’t changed since the SD14 and its square shape looks a little dated when compared with the more rounded profiles offered by other manufacturers. The hand-grip is generous and has a moulded indent for the second finger of the right hand, which positions the index finger just above the shutter button.
Surrounding the shutter button is a command dial (C-dial), which is used to adjust selected settings. Between the grip and the lens mount is an AF-Assist LED. The lens release button is located below it near the lower edge of the lens mount.
Rear view of the Sigma SD15 showing the menu system. (Source: Sigma.)
The rear panel has been updated with a larger, higher-resolution monitor and some new buttons have been added to provide direct access to the ISO settings and metering and AF modes. These buttons are clustered to the left of the moulded thumb rest on the right hand side of the panel. In addition, the Function, AEL, exposure compensation, ISO and data panel light button have textured tops to make them easy to locate without removing your eye from the viewfinder.
Five buttons are ranged along the left side of the monitor screen accessing the Menu, Playback, Information, Modify Menu and Delete buttons. The modification menu lets you lock, mark and rotate selected images and accesses slideshow playback of shots on the memory card.
Above the top left corner of the monitor is a Function button. Pressing it calls up a graphic display replicating the view seen through the viewfinder.
In the top left corner you’ll find the battery level indicator, exposure mode, metering mode and ISO setting. Right of these icons is a grid-like display showing the focusing frame with the positions of the AF sensors.
Aperture, shutter speed, exposure compensation, number of shots remaining and AF mode icons are ranged down the right side of the frame, while along the bottom of the frame are the flash and remote control settings. You can toggle through the icons on the bottom toolbar with the horizontal buttons on the arrow pad and select settings with the OK button. Other icons are selected via dedicated buttons or dials and the arrow pad.
The Camera Info button also displays current camera settings but includes a graphic that replicates some of the functions accessed via the QS button on the right of the monitor. The QS button is the same as on Sigma’s DP series of compact cameras, with two screens. The blue screen contains flash, ISO, metering and flash modes, while the orange screen covers white balance, image size and quality and Colour Mode settings.
AEL and exposure compensation buttons are located near the top of the rear panel on the right hand side, while an arrow pad with a central OK button lies below it. Below the arrow pad is a Cancel button, which is used for ending slideshow displays or switching out of a display mode.
Top view of the Sigma SD15 without a lens and with the drive dial set to power-on. (Source: Sigma.)
The top panel carries two dials that cover the drive and shooting modes. The drive dial contains settings for power off, single frame and continuous shooting, two- and ten-second self-timer modes, mirror lock-up and auto bracketing. Only four settings are provided on the shooting mode dial: P, A, S and M.
A small and rather dim LCD data display is located to the right of the shooting mode dial. It displays aperture, shutter speed. ISO, exposure and flash compensation, auto bracketing, metering mode, remote control and battery data plus a frame counter. Between this panel and the shutter button is a button for illuminating this display.
The viewfinder has a fixed focusing screen and covers 98% of the sensor’s field of view. Aperture, shutter speed and exposure compensation figures are displayed along its lower edge. AF target selection is overlaid on the scene but displays of ISO and metering mode are not provided.
The SD15 is the first Sigma DSLR to use SD and SDHC cards instead of CF. The smaller slot in the right side of the camera body probably accounts in part for the lighter weight of the new model. The change will be appreciated by owners of DP-series cameras, which from the start have used SD cards.
Side views of the SD15 showing the SD card slot at the x-synch socket for external flashes. (Source: Sigma.)
Other key functions are as you would expect for an enthusiast’s camera. Shutter speeds range from 30 seconds to 1/4000 second and there’s a mirror-up mode, two self-timer options and AE bracketing. Five frame bracketing has now been added to the Auto Bracketing function so users can choose between three and five frames and adjust the bracketing steps in 1/3EV increments across a range of +/- 3EV.
The metering system has a new 77-segment AE sensor and improved algorithms which work with the AF sensors to improve exposure accuracy. There’s also an x-synch socket that enables the camera to be used with off-camera flash guns. Below it is a rubber-covered compartment containing USB 2.0, AV-out and DC-in ports.
The built-in flash rises well above the lens axis and covers viewing angles as wide as a 17mm lens with a guide number of 11. Maximum synch speed is 1/180 second and S-TTL automatic exposure control works with all exposure modes. Slow synch and rear curtain synch are supported.
Sigma claims the supplied BP-21 lithium-ion battery will support approximately 500 shots/ charge, which is adequate but not a match for highly specified professional cameras. Beside the battery compartment is a metal-lined tripod mounting that is located in line with the lens axis.
Like its predecessors, the SD15 is a purist’s camera that has been designed for still photography. It provides no support for video recording – nor does it include live viewing. If you want image stabilisation, it must come with the lens, although Sigma has reduced mirror slap (and vibration) through use of two motor systems which minimise the effect of mirror movements on the camera.
No built-in sensor vibration system is provided for sensor dust removal. However, none is necessary as, unlike other DSLRs, the mirror box is sealed off behind a glass cover just behind the lens mount. Nevertheless, camera shake can be an issue in low light levels and must be eliminated if you want high-quality photos.
The edges of this dust protector fit into the lip around the mount, preventing dust from getting on the sensor and reflex mirror. It is quite easy to keep clean and can be removed if for sensor cleaning, should it be necessary.
The built-in dust protector that stops contaminants from getting into the mirror box.
No scene pre-sets are provided – and none are really required in a camera designed for raw file capture. All the necessary adjustments can be made in Sigma Photo Pro 4 when the raw files are converted into editable formats.
However, to satisfy JPEG shooters, the Colour Mode on the orange page of the QS menu provides seven pre-sets (Standard, Vivid, Neutral, Portrait, Landscape, B&W and Sepia) that optimise camera settings for certain types of shots. The menu also provides a Picture Settings adjustment that lets you tweak saturation, contrast and sharpness and choose between the sRGB and Adobe RGB colour spaces.
The AF system is pretty basic and has only five sensors, none of which are cross-type. It’s a bit slow and tends to hunt in low light levels and the AF-assist lamp has limited reach so shooting nightscapes usually requires manual focusing.
Sensor and Image Processing
We’ve been following the development of the X3 sensor since it was first released in the SD9 in 2002 and nothing much has changed since then, save for Sigma’s purchase of Foveon in November, 2008. We’ve provided a detailed explanation of how this sensor works in previous reviews of Sigma cameras, most recently in our review of the SD14.
Front view of the SD15 with lens and dust protector removed to show the Foveon sensor. (Source: Sigma.)
In summary, the Foveon sensor is structured in three layers, rather like colour film. The layers of photosites are embedded in silicon and take advantage of the fact that red, green, and blue light penetrate silicon to different depths, as shown in the diagram below.
The diagrams above show the similarities and differences between conventional (top) and Foveon sensors (below). (Source: Sigma.)
The bottom layer records red, the middle layer records green, and the top layer records blue. Image data for each colour can be extracted from the related layer without requiring filtration (as in regular CCD and CMOS sensors). This means the full sensor resolution is available for each colour and no interpolation is required.
However, there’s a downside to the Foveon sensor: even though Sigma claims an effective resolution of 14.45 megapixels, the largest images are only 2640 x 1760 pixels in size (or just over 4.6 megapixels). This is the file size Imatest measures for both JPEG and raw images – and this makes it difficult to compare Sigma cameras with cameras that have conventional sensors.
When you shoot JPEGs, the largest image files are between 3.3MB and 1.4MB in size, which is pretty small by modern standards and a good argument for using the JPEG setting only for shots that will be used online. Shoot raw files and the images are between about 12MB and 17MB in size, depending on the amount of detail in the shot.
Despite their relatively low image resolution, images from the Foveon sensor are cleaner and more colour-rich than those from sensors with Bayer colour filters. Camera response times should, in theory, also be faster, although we’ve found little evidence to support this premise.
With the SD15, Sigma has introduced a new TRUE (Three-layer Responsive Ultimate Engine) II image processor, which it claims improves the processing speed and overall image quality from the camera. A new DDR II buffer memory gives the SD15 twice the capacity of the SD14. However, capture rates are still very modest as the new camera has a maximum continuous shooting speed of only three frames/second, although it can now store up to 21 X3F.RAW frames in each burst.
Also modest is the SD15’s sensitivity range, which spans from ISO 100 to 1600. You can extend this range to ISO 50 and ISO 3200 via the Extended Mode setting in the camera setup menu. Bulb exposure time can also be lengthened from 30 seconds to 120 seconds with this setting.
Playback and Software
Nothing much has changed here. Playback options are pretty standard and include single and nine-frame index views plus up to 10x magnification in ten steps. There’s a jump mode that lets you step through batches of images a page at a time and slideshow playback.
The normal thumbnail-plus-shooting data display is available and you can access a brightness histogram in Quick Playback mode or RGB histograms with normal playback. A highlight alert warning can be set to display in the menu and toggled on and off with the OK button on the arrow pad when shots are displayed.
The bundled software is the latest version (v. 4.2) of Sigma’s Photo Pro, which is the best (and currently only) application for processing X3F.RAW files. (It’s a minor update of version 3, which we covered in detail in our review of the SD14.)
If you want larger files for printing, you can double the output file size by selecting ‘Double’ in the top line of the Processing Options (circled in red in the screen grab above). The process involves interpolation but is very effective and the resulting files are easily printable to A3+ size.
Since the SD15 has been designed for raw file capture, unless otherwise specified, all test shots were taken as X3F.RAW files and converted with Sigma’s Photo Pro 4.2. We deliberately carried out our white balance tests with JPEG files because colour balance is easily adjustable when raw files are converted into editable formats. We also used JPEGs for the lens focal length/aperture tests to maintain consistence with tests of other lenses.
We reviewed the camera with Sigma’s AF 17-70mm f/2.8-4 DC Macro OS HSM, which is a good performer and has build quality to match the SD15. A review of this lens conducted with the Canon EOS 40D body, is available here.
All test images were recorded with the standard and neutral picture modes, which produced JPEGs that were slightly flat. JPEG images straight from the camera were also a little soft at the default sharpening setting and X3F.RAW files benefited from slight sharpening during processing as well.
To get the best results – and rich colours that characterise Foveon images – you need to shoot with the Vivid setting or work on your images with an image editor. Even slight tweaking of brightness and contrast can make significant improvements.
As expected, performance in our Imatest tests was similar to the SD14. Differences between X3F.RAW and JPEG files were relatively small and both exceeded expectations for the sensor’s resolution by a generous margin that was maintained through most focal length and aperture settings.
Best performance was between f/4 and f/8, with diffraction kicking in at around f/11. slight edge softening was noticeable at wider apertures. The graph below, which is biased towards wider apertures, shows the results of our Imatest tests, based on JPEG files.
Lateral chromatic aberration was mainly negligible, wandering into the ‘low’ band at longer focal length settings. The graph below shows the results of our Imatest tests, based on JPEG files.
Resolution remained high at most ISO settings, with the differences between raw and JPEG files widening as sensitivity was increased. The graph below shows the results of our Imatest tests that covered JPEG files and X3F.RAW processed in Sigma Photo Pro 4.2.
Test shots using long exposures delivered better results than we found with the previous model, although noise was evident at ISO 1600 – and image quality deteriorated severely with the ISO 3200 setting, where only raw files can be recorded. Flash exposures were evenly exposed and image quality was good up to ISO 1600 but poor at ISO 3200.
Auto white balance performance was noticeably better than we found with the SD14. The residual warm cast in JPEG files shot under incandescent lighting was comparatively slight and easily correctable, while images shot under fluorescent lighting retained a natural colour balance.
Camera response times were slightly better than we found with the SD14. However, autofocusing was a bit patchy; fast in bright conditions but erratic and plagued by hunting in very low light levels. Manual focusing is advisable after dark.
The review camera powered up within a second and shot-to-shot times averaged 1.1 seconds without flash and 1.9 seconds with. It took 3.2 seconds to process each JPEG file and 3.8 seconds for each raw file.
In the continuous shooting mode, frames were recorded at just under the specified three fames/second speed. However, processing appeared to be on-the-fly as it took approximately 35 seconds to process a burst of 10 JPEGs and just under 40 seconds for a burst of 10 X3F.RAW files, going by the indicator LED on the rear panel.
Many features in the SD15 have been improved in the three years that have passed since we reviewed the SD14. However, the Foveon sensor remains the same and, even though JPEG performance has improved dramatically, this camera only delivers its best results from X3F.RAW files. And you must be prepared to work on them, both with the supplied raw file processing software and subsequently in a capable image editor.
Relative to other DSLRs on the market, the SD15 remains pretty pricey. Potential purchasers will need to weigh up the advantages of this camera against the many functions that are either missing or limited when compared with DSLRs from some other manufacturers.
In September, 2010, Sigma announced a new DSLR camera, the SD1, which uses a new Foveon sensor measuring 24 x 16 mm. This sensor has a 1.5x crop factor, the same as Nikon, Pentax and Sony’s APS-C DSLRs and produces 4800 x 3200 pixel images (just under 15.4 megapixels in size).
As with the SD15 and its predecessors, Sigma combines the resolution of each colour layer and is claiming a resolution of 46 megapixels for the new camera. The TRUE II image processor used in the SD15 is included in the SD1, which also has the same LCD monitor.
Buy this camera if:
– You want a DSLR camera that will deliver sharp, colour-rich images and are prepared to work with raw files.
– You want a camera with P, A, S and M shooting modes – and no fancy additions.
– You want a DSLR with a built-in auto flash plus useful flash modes and exposure adjustments.
Don’t buy this camera if:
– You want to shoot video.
– You require easy-to-use automated shooting modes.
– You want simultaneous RAW+JPEG capture.
Raw images converted with Sigma Photo Pro 4.2 with no additional adjustments.
(Unless indicated otherwise, all images were recorded as X3F.RAW files and converted into JPEG format with Sigma Photo Pro 4.2)
Auto white balance with incandescent lighting. (JPEG original.)
Auto white balance with fluorescent lighting. (JPEG original.)
30-second exposure at ISO 100; 25mm focal length, f/4.5.
10-second exposure at ISO 800; 25mm focal length, f/5.6.
5-second exposure at ISO 1600; 25mm focal length, f/5.6.
5-second exposure at ISO 3200; 25mm focal length, f/8.
Flash exposure at ISO 100; 70mm focal length, 1/60 second at f/4.
Flash exposure at ISO 800; 70mm focal length, 1/60 second at f/4.
Flash exposure at ISO 1600; 70mm focal length, 1/60 second at f/4.5.
Flash exposure at ISO 3200; 70mm focal length, 1/30 second at f/4.5.
Skin tones;42mm focal length, ISO 800, 1/50 second at f/5.
Close-up; 70mm focal length, ISO 200; 1/125 second at f/5.
50mm focal length, ISO 100; 1/250 second at f/11.
70mm focal length, ISO 200; 1/320 second at f/8.
70mm focal length, ISO 100; 1/125 second at f/5.6.
60mm focal length, ISO 100, 1/200 second at f/8.
Image sensor: 20.7 x 13.8mm Foveon X3 Direct Image CMOS sensor with three layers of 2688 x 1792 photosites (14.45 megapixels effective)
A/D processing: 12-bit
Lens mount: Sigma SA bayonet mount
Focal length crop factor: 1.7x
Image formats: X3F.RAW (lossless compression), JPEG (Exif 2.21)
Image Sizes: RAW – 2640 x 1760; JPEG – 2640 x 1760, 1872 x 1248, 1312 x 880 (3 levels of compression selectable)
Image Stabilisation: Lens-based
Dust removal: Protective glass barrier
Shutter speed range: 30 seconds to 1/4000 second plus Bulb (up to 120 seconds in Extended Mode; flash synch at 1/180 second
Exposure Compensation: +/- 3EV in 1/3 EV increments
Exposure bracketing: 3 frames in 0.3EV steps up to +/- 3EV or 5 fames in 0.3EV steps up to +/- 1.7EV
Self-timer: 2 or 10 seconds delay
Focus system: TTL phase difference detection system with 5 sensor points (centre point cross type); auto/manual AF point selection; white AF-assist light
Focus modes: Single AF, Continuous AF (with AF motion prediction function), Manual Focus
Exposure metering: 77 segment evaluative metering, spot metering, centre area metering, centre-weighted average metering
Shooting modes: Program AE, Aperture priority, Shutter priority, Manual
Picture Style/Control settings: Standard, Vivid, Neutral, Portrait, Landscape, B&W, Sepia
Colour space options: sRGB, Adobe RGB
ISO range: Auto (ISO 100-200), with flash (ISO 100-400), manual settings ISO 100, 200, 400, 800 and 1600 (ISO 50 and ISO 3200 with Extended Mode)
White balance: Auto, Sunlight, Shade, Overcast, Incandescent, Fluorescent, Flash and Custom
Flash: Built-in Manual Pop-up, GN 11 (metres at ISO 100), 17mm lens angle covered
Flash exposure adjustment: +/- 3EV in 1/3 EV increments
Sequence shooting: Up to 3 fps; max. 21 frames (RAW or JPEG)
Storage Media: Single slot for SD/SDHC cards
Viewfinder: Pentaprism with 98% FOV coverage, 0.8x magnification, 18mm eye relief, fixed all matt focusing screen, dioptre adjustment from -3.0 to +1.5 dpt
LCD monitor: 3.0-inch TFT LCD with 460,000-dots and 100% field of view coverage
Live View modes: No
Data LCD: Yes
Playback functions: Single-frame, Index (4 or 9 frames), Enlarge (7.2x to 14x), Slideshow, Picture rotation (auto mode available), Histogram (independent luminance/RGB available), Shooting information
Interface terminals: USB 2.0, Video Out (NTSC/PAL)
Power supply: BP-21 rechargeable lithium-ion battery; rated for approx. 500 shots/charge
Dimensions (wxhxd): 144 x 107.3 x 80.5 mm
Weight: 680 grams (without battery and card)
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RRP: $1,499 body only; $1,699 with Sigma 18-50mm OS lens
Rating (out of 10):
- Build: 9.0
- Ease of use: 8.5
- Autofocusing: 8.0
- Image quality: JPEG – 8.5; X3F.RAW – 9.0
- OVERALL: 8.5