Sigma SD10Sigma's digital SLR uses Foveon's latest "X3" sensor technology to boost ISO and reduce image noise.<<Optics :(Previous) | (Next): Shutter Lag & Cycle Time Tests>> Page 6:Exposure & FlashReview First Posted: 10/26/2003 |
Exposure
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Exposure control is straightforward on the SD10, 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 SD10's though, the camera will simply use the largest aperture available to it, and set the shutter speed accordingly.
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In Manual mode, the user can control aperture and shutter speed simultaneously. Aperture settings will vary with the lens in use, but by default shutter speeds range from 1/6,000 to 15 seconds. With the default settings, when the ISO is set to 400 or 800 though, the maximum exposure time drops to four seconds, limiting the SD10's low-light capabilities a fair bit. It is possible to get around this by setting the SD10 to Extended mode, where an ISO 1600 setting becomes available, along with the ability to select shutter speeds from 1/6000 to 30 seconds in all ISO ratings. The SD10 also has a bulb setting, although curiously this is limited to exposures of approximately 15 seconds or less. Like the SD9, the bulb setting is not available in all ISO ratings by default - just ISO 100 and 200; if you put the camera in extended mode, it is available in every ISO rating however. Another noteworthy change from the SD9 is that for exposures of five seconds or longer, the camera automatically locks the mirror up a couple of seconds before starting the exposure, rather than requiring the user switch to the mirror lockup mode.
To determine the exposure value, the SD10 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 SD10'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-third-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 was pleased to see a noticeable improvement over the SD9 - that camera used half-stop exposure adjustments which are just too coarse, often leaving you choosing between blowing the highlights or having a dull, underexposed image. With the SD10, you have the ability to make finer-grained adjustments when capturing the photo, as well as still having the ability to adjust the photo post-capture (thanks to Sigma's excellent software and the SD10's raw-format data files). Kudos to Sigma for listening to the feedback given on the SD9!
If you're uncertain about the exposure, the SD10'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 +/-0.3 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 SD10 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 SD10 offers sensitivity settings equivalent to ISO 100, 200, 400, and 800 by default, adjustable by pressing the ISO button and turning the Command dial. - Remember though, that ISO settings of 400 or higher limit the maximum exposure time to four seconds by default. By tapping the Func button until the LCD info display reads "Std" and then holding it whilst turning the Command dial, you can set the camera to an Extended mode where the maximum ISO rating is raised to 1600, and the limitations on exposure time are removed (all ISO ratings then allow exposures up to 30 seconds, and use of the 15 second max. Bulb mode). Image noise has been greatly improved over the earlier SD9 camera, somewhat relaxing the ISO/shutter time limitations I found with that model. While short-exposure noise now appears to be very competitive with conventional sensors though, noise still does seem to be somewhat of an issue with the X3 technology at long exposure times, hence the limitation on maximum shutter time as the ISO increases. If you intend to do a lot of night shooting, this (somewhat lessened) limitation of the SD10 might still 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 SD10 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 SD10'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 SD10 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 SD10's exposure system, you'll need to use one of Sigma's dedicated flashes, such as the Sigma EF500 DG ST SA-N or EF500 DG Super SA-N flash unit. Both flash units work with the SD10's TTL metering system to give accurate exposures regardless of the lens you have attached. In addition, the EF500 DG Super SA-N flash allows for wireless TTL flash, using one EF500 DG Super SA-N unit on the hotshoe and a second positioned somewhere off-camera. The original SD9 can fire the remote slave, but cannot do wireless TTL flash with it. The hot shoe does have the standard center contact, 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 SD10'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. As with the SD9, Sigma estimates that at the highest resolution setting, the SD10 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 SD10 at 1.9 frames/second for large files, and 2.4 frames/second for small ones.)
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