Sigma SD9Sigma's digital SLR uses Foveon's "X3" sensor technology to deliver more detail per pixel!<<Optics :(Previous) | (Next): Shutter Lag & Cycle Time Tests>> Page 6:Exposure & FlashReview First Posted: 11/09/2002 |
Exposure
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Exposure control is straightforward on the SD9, with a range of external dials and buttons to adjust settings. The camera offers a full range of exposure control, with Program AE, Aperture Priority, Shutter Speed Priority, and Manual exposure modes available via a Mode Selector on the top panel. Program AE mode lets the camera control both aperture and shutter speed, while Aperture Priority and Shutter Speed Priority modes let the user control one of the exposure variables. In Program AE mode, I really appreciated the automatic "vari-program" operation, that let me select different combinations of shutter speed and aperture simply by turning the command dial (C-Dial in Sigma parlance). I find variable program modes like this more useful than pure aperture or shutter priority modes. Their advantage is that they let the camera set the aperture or shutter speed as needed to get a good exposure, but let the photographer adjust the exposure parameters toward larger or smaller apertures, higher or lower shutter speeds. If you're in shutter priority mode and select a shutter speed that's too fast for the maximum aperture of the lens you're using, you'll end up with an underexposed shot. With a vari-program approach like the SD9's though, the camera will simply use the largest aperture available to it, and set the shutter speed accordingly.
In Manual mode, the user can control aperture and shutter speed simultaneously. Aperture settings will vary with the lens in use, but shutter speeds range from 1/6,000 to 15 seconds. When the ISO set to 200 or 400 though, the maximum exposure time drops to one second, limiting the SD9's low-light capabilities a fair bit.
To determine the exposure value, the SD9 uses an eight-segment, Evaluative metering system, which divides the image into eight regions and takes individual readings from each section. The readings are evaluated (not simply averaged) to determine the best overall exposure values based on a combination of brightness and contrast between the different areas. Besides the default evaluative metering though, the top-panel metering button lets you opt for Center or Center-Weighted modes as well. Center mode, traditionally called "spot" metering on other cameras, reads the exposure only from a tiny area in the center of the frame. Center-Weighted metering reads a larger area in the center of the frame, and bases the exposure on that, ignoring the periphery of the image.
An AEL (Auto Exposure Lock) button locks the exposure, helpful when shooting off-center subjects. You simply frame the portion of the subject that you want to expose for in the center of the frame and press (and hold) the AEL button while half-pressing the shutter button to lock the exposure, and then reframe the shot for capture. The "lock" is held only as long as you hold down the AEL button with your thumb, with the exposure not changing when you release and press the shutter button again. (Which triggers the autofocus system again.) Interestingly, the exposure will continue to be held even if you snap multiple shots. This AEL operation is different from most other cameras I've tested. Most lock with a single press of the AEL button (not requiring it to be held down), but release again as soon as you trip the shutter, or press the AEL button a second time. I found it a little awkward to have to keep my thumb on the SD9's AEL button, but liked being able to hold the lock across multiple exposures.
In all exposure modes except for Manual, you can adjust the camera-determined exposure from -3 to +3 exposure equivalents (EV) in one-half-step increments. (This is a wider than average range for most digicams, but typical of that offered by professional-level digital SLRs.) This is an area where I felt the SD9's designers fell down a bit. It's been my experience that digital cameras really need finer-grained exposure control than do film cameras, with 1/3-stop increments being about right. Half-stop exposure adjustments are just too coarse, often leaving you choosing between blowing the highlights or having a dull, underexposed image. With the SD9, you do at least have the ability to adjust the photo post-capture, thanks to Sigma's excellent software and the SD9's raw-format data files, but I'd still really like to see at least an option for 1/3-stop exposure adjustments.
If you're uncertain about the exposure, the SD9's Autoexposure Bracketing mode (listed as "AB" on the Drive dial) captures three images at different exposures (one at the metered exposure, one underexposed, and one overexposed). You can then choose the best exposure from the three. AB mode lets you select exposure increments between exposures of anywhere from +/-0.5 EV to +/-3.0 EV, a wide range. AB is activated by setting any nonzero value in the LCD data readout when the Drive Dial is in this position. It's disabled by setting the exposure increment back to zero. NOTE that the AB setting applies regardless of the shooting mode selected (single or continuous exposure). While some cameras only apply auto bracketing to continuous shooting mode, the SD9 implements it for single shots as well. Thus, the camera will calculate and vary exposure across groups of three shots, even if you're just shooting single frames. - This makes it important to remember to turn off the AB function when you're done with it, so it doesn't skew exposures on it when you're not expecting it to.
The SD9 offers sensitivity settings equivalent to ISO 100, 200, and 400, adjustable by pressing the ISO button and turning the Command dial. - Remember though, that the higher ISO settings limit the maximum exposure time to one second. Image noise does appear to be an issue with the X3 sensor technology, hence the limitation on maximum shutter time as the ISO increases. If you intend to do a lot of night shooting, this limitation of the SD9 might give you pause. White balance options include Auto, Sunlight, Shade, Overcast, Incandescent, Fluorescent, Flash, and Custom (the manual setting), and are adjusted through the LCD menu. Because the SD9 captures all files in the raw sensor format, any other color or image adjustments are handled via the camera's exceptionally capable host software.
The SD9's self-timer function features a two-second and a 10-second countdown. In either mode, the shutter is released the specified amount of time after the Shutter button is fully pressed. Both self-timer modes are accessed via the Drive Mode dial on top of the camera.
Flash
The SD9 does not have a built-in flash unit. It does, however, feature an external flash hot shoe on its top panel. For full integration with the SD9's exposure system, you'll need to use one of Sigma's dedicated flashes, such as the Sigma EF-500 DG Super SA or EF-500 DG ST SA flash unit. Both flash units work with the SD9's TTL metering system to give accurate exposures regardless of the lens you have attached. The hot shoe does have the standard center contact though, so any conventional "dumb" flash unit will work fine too, although you'll forego Sigma's advanced TTL metering.
Continuous Shooting
Set via the Drive Mode dial, the SD9's Continuous Shooting mode captures a rapid burst of images for as long as the Shutter button is held down. Actual frame rates and the maximum number of frames in each burst will vary depending on the amount of available memory space, as well as the file size and quality settings selected. Sigma estimates that at the highest resolution setting, the SD9 will capture as many as six frames at approximately 1.9 frames per second. At the lowest resolution setting, Sigma estimates the camera will capture a maximum of 30 frames at approximately 2.5 frames per second. (These figures seem pretty accurate: In my own tests, I clocked the SD9 at 1.88 frames/second for large files, and 2.67 frames/second for small ones.)
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