On February 24, 2002, at the Photo Marketing Association International 2002
show, Sigma announced the SD9 single-lens reflex, their first digital camera. The
full specs are listed in a table at the bottom of the article, but most notably
this is the first camera incorporating the new Foveon x3 CMOS sensor technology.
We were able to see the SD9 model on the PMAI 2002 show floor but we weren't able
to handle it. The 3.5-megapixel, 12-bit-per-color camera should be available
later this spring. It takes Sigma SA-mount lenses and multiplies their effective
focal length by 1.7. The SD9 can be preordered for
$2999.95 at Ritzcamera.com..
Foveon X3 technology
| Test Type |
CCD Camera
with Color Filter Array |
CCD Camera
with Anti-Alias Filter and
Color Filter Array |
Foveon X3 |
| Color Artifacts |
|
|
|
| Sharpness |
|
|
|
| Color Detail |
|
|
|
These images apparently came from taking images of the same scene and it is
shown below in a "degraded" through jpeg processing state for
simplereference.
Another comparison image illustrating these three points where on the left we
have the color filter array image and on the right the foveon X3 version of the
same image.
How it works
First, some background. Today's typical CCD/CMOS imager achieves "color"
images by sampling at each point on the array underneath a mosaic of color
filters, which allows it to sample the visible light spectrum under these
filters. Typically the point from which data are collected is called a
photosite. The mosaic of filters looks like
Each filter passes one color of light to the imaging sensor element
underneath.
The mosaic is not an equal mix of colors, but rather a ratio of green:blue:red
of 2:1:1 as illustrated below:
This is done because our eyes are more sensitive to green light. Why don't
digital cameras use three CCDs and split the incoming light with a color prism?
The answer is they could, and in fact this is how 3-CCD camcorders work. However,
it is expensive and alignment is difficult at the higher resolutions of still
photography.
Once the data are read from the sensor the manufacturer's proprietary
upsampling/interpolation algorithm computes effective red, green and blue data at
each "pixel". In actuality only 1/2 the pixels for green were measured and 1/4 of
the pixels for each of red and blue.
More on traditional CCDs and color filter arrays:
What Foveon does
The picture below illustrates Foveon's X3 technology for measuring the light
red, green, and blue at each pixel. All three layers are made from standard
silicon, the longer wavelengths of light have deeper absorption depths. So if you
place photodiodes at those depths one can get measurements that will then allow
one to compute the red, green, and blue light incident on the pixel.
If you want to dig deeper into this the apparent relevant patent is
#5,965,875 by Richard Merrill Foveon's Senior Scientist and Chief Sensor
Architect. He is also mentioned in several articles related to the Foveon 16
megapixel sensor announced last year.
The chip can also be used for video applications. One can address the sensor
in such a way that the whole sensor may be redivided into larger pixel sizes,
summing up the the data of the smaller pixels making up the larger pixel into the
output data for the larger pixel. This makes it easy to use the sensor for high
frame rate video applications. One can at best get about 3 frames per second out
of the chip at the highest resolution. For video applications one would need to
take data out at a reduced resolution. Given what we said above about 3-panel
video cameras that cost about 1500 dollars today, Foveon may cause some
improvement in performance for consumer video cameras.
Conclusion
The interesting question remains open until Sigma starts delivering cameras:
Will 3.5 RGB pixels look better than 6 million color array pixels (Canon D60,
Nikon D100) ?
Sigma SD9 Specifications
| Camera Type |
Interchangeable-Lens SLR-Type Digital Camera |
| Storage Media |
CompactFlashTM (CF) (TypeI/II), IBM MicrodriveTM |
| Image Sensor Size |
20.7 mm; W13.8 mm; |
| Usable Lenses |
Sigma SA mount lenses |
| Actual Field of View |
Equivalent to 1.7x the focal length of lens when used on a 35mm SLR |
| Lens Mount |
SA Bayonet Mount |
| Image Sensor |
FOVEON X3 (CMOS) |
| Resolution |
Total Pixels: 3.54 million pixels W3 Effective; 3.43 million pixels W3 |
| Aspect Ratio |
3 : 2 |
| Image Recording Format |
Lossless compression RAW Data (12bit) |
| Image File Size |
(1) HI 2268 W 1512 W3 (Approx. 8MB) (2) MED:2268x756 x3 (Approx. 4MB) (3)
LOW:1134x756 x3 (Approx. 2MB) |
| Interfaces |
IEEE1394, USB (1.1), Video Out (NTSC/PAL) |
| White Balance |
8type |
| Viewfinder Type |
Pentaprism SLR Viewfinder |
| Viewfinder Frame coverage |
98% horizontal, 97% vertical |
| Viewfinder Magnification |
0.77x (50mm F1.4;) |
| Eyepoint |
18mm |
| Diopter Adjustment Range |
-3dpt +1dpt |
| Auto Focus Type |
TTL phase difference detection system |
| AF Operating Range |
EV2 ~ +18 (ISO100) |
| Focus Mode |
Single AF, Continuous AF (w/ AF Predict function) |
| Metering Systems |
8-segment Evaluative Metering, Center Metering, Center-Weighted Average
Metering |
| Metering Range |
EV-1 ~ 20 (with 50mm F1.4 at ISO100) |
| Exposure Modes |
(P)Program AE with program shift function, (S) Shutter Speed Priority AE,
(A);Aperture Priority AE, Metered Manual |
| ISO Sensitivity |
ISO 100, 200, 400 |
| Exposure Compensation |
13EV (in 1/2steps) |
| AE Lock |
Pushbutton type (exposure settings are locked while the button in
depressed) |
| Auto Bracketing |
Three Different Exposure Levels; Appropriate, Under and Over Exposure;
Maximum variation of 13EV in 1/2 EV steps |
| Shutter Type |
Vertical-travel metal focal plane shutter electronically controlled through
entire speed range |
| Shutter Speeds |
1/6000 to 30sec., Bulb |
| External Flash Synchronization |
Hot shoe (contact X, synchronized at 1/180-sec. or less, with dedicated flash
linking contact) |
| LCD Monitor Type |
1.8", Color TFT LCD with 130,000dot low-temp. polysilicon Coverage Area :
100% Backlight : White LED |
| Reviewing Images |
Single-Image Display, Zoom-in Display, 9 images thumbnail display, Slide
Show |
| Menu Languages |
Japanese / English / French / German |
| Power Source |
Battery: Lithium CR123A W 2pcs batteries : Lithium CR-V3 W 2pcs, or A
Alkaline Dry Cell X4pcs or Ni-MH X4pcs, AC Adapter |
| Dimension and Weight |
Dimensions : 152(W)mm W 120(H)mm W 79(D)mm / 5.9in (W)X 4.7in (H)X3.1in(D)
Weight : 803g/28.3 oz |
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