Sigma SD10Sigma's digital SLR uses Foveon's latest "X3" sensor technology to boost ISO and reduce image noise.<<Viewfinder :(Previous) | (Next): Exposure & Flash>> Page 5:OpticsReview First Posted: 10/26/2003 |
Optics
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The SD10 is an interchangeable-lens SLR, with the lens attached via an SA-type, bayonet lens mount on the front panel. The camera will be offered in three configurations - body only (ie. with no lens included), or as one of two product bundles with either an 18-50mm F3.5-5.6 DC lens, or a bundle with both that lens and also a 55-200mm F4-5.6 DC lens. Maximum aperture, focal length, and focusing distance range will thus vary with the particular lens being used. A small release button below the bottom of the mount releases the lens, allowing it to turn and slide out of the mount. The position of the release button is comfortably close to the hand grip, making it easy to quickly switch lenses (as opposed to cameras that place the release button on the opposite side of the lens - requiring some extra manual dexterity to hold the camera and lens whilst pressing the button). A Depth of Field Preview button (next to the top left side of the lens mount, when viewing the camera from the front) stops the lens down to the designated aperture setting, so that you can preview the depth of field you'll have in the shot through the viewfinder - of course with the limitation that less light will make it to the viewfinder depending on the aperture you're stopping down to.
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Because most current digital SLRs have a sensor that's smaller than a 35mm film frame, they have what's referred to as a "focal length multiplier" relative to 35mm cameras. This is the factor by which the camera reduces the field of view (effectively magnifying the image) with a given lens, relative to how that lens would function on a 35mm camera. Since the sensor size of the SD10 is identical to that of the SD9, it has the same focal length multiplier of 1.7x - which means that on either the SD9 or SD10, a "normal" 50mm lens will show the same field of view as an 85mm lens on a 35mm camera. This makes it difficult to do true wide angle photography with either camera. By way of example, the normally "extra wide" 20-40mm zoom lens Sigma shipped along with my eval camera is the equivalent of a 34-68mm zoom on a 35mm film body. Focal length multiplier is a fact of life with all but a few of the digital SLRs currently on the market, but 1.7x is a higher ratio than any I'm aware of on other current models. (Most run between 1.5 and 1.6x.) Not a crippling defect by a long shot, but a factor to consider if you like wide angle shots.
The SD10 offers Single and Continuous autofocus modes (manual focus is activated via a switch on the lens, if available). Single AF adjusts focus only when the Shutter button is halfway pressed, using a TTL phase difference detection system. Conversely, Continuous AF mode constantly adjusts the focus, without waiting for you to press the Shutter button. Continuous AF uses an AF Predict function, which "predicts" where the subject will move to next, based on its current pattern of movement. Combined with the Sports Finder viewfinder display, the SD10's Continuous AF system makes tracking moving subjects a little easier.
I don't have any objective test for autofocus speed, so I hesitate to say too much on the subject here, not wanting to color my reviews with purely subjective impressions. Sigma told us that the autofocus system of the SD10 had been improved overall as compared to the SD9 (with the most notable improvements in low-light focusing). In my own testing of the camera, I did notice that the camera seemed to get confused and give up quite a bit less often than the SD9 did, but I I still found the SD10's AF system had a tendency to "hunt" back and forth for the correct focus setting a bit more than I'm accustomed to with other digital SLRs. Correlating with what Sigma told me was most improved with the focus system, I felt low light focusing was actually fairly good - the camera would focus reasonably reliably down to light levels of about 1/8 foot-candle (about 1.4 lux), if given a fairly good subject. (A nice, sharp, high-contrast edge.) Occasionally, it could manage to achieve focus as low as 1.0 lux, although it would take repeated attempts and some focus hunting to do so. Overall, the SD10's AF system is certainly a noticeable improvement over the SD9, but could perhaps still use some further improvement.
The SD10 has a "dust cover" right behind the lens mount, protecting the mirror/shutter/sensor chamber. The idea is to keep dust from reaching the sensor, an issue for most digital SLRs. Dust on the sensor is a much more severe problem with digital SLRs than it is on film-based cameras, since the film is more or less continuously cleaned as it passes through the light seal on the cannister. With a digital SLR though, any dust that makes its way into the camera body and ends up on the sensor is there permanently, or at least until you clean the sensor, a delicate operation that's best avoided if at all possible. Sigma's approach seems like a good one, for two reasons. First, cleaning the dust cover is a relatively easy and risk-free proposition. Second, any dust that settles on the dust cover won't be imaged, because it's too far up the optical path. (In other words, it won't cast sharp shadows on the sensor, and so won't affect the images.
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There are two downsides to the dust cover approach though. First, it introduces two additional optical surfaces into the light path, potentially affecting sharpness, aberration, flare, etc. The second issue is only a potential downside, but based on my eval unit, could be a very real one: If dust does manage to get into the camera body, you've got an even bigger problem that if the dust cover wasn't there, because you'll have to remove it to get the dust out. When I reviewed the SD9, I noted a significant quantity of dust behind the dust cover - probably introduced in manufacturing, since it had come directly to me from Sigma in Japan. In the comparison photos above, the SD10 is compared to Canon's EOS Digital Rebel. The SD10 had Sigma's 50mm f/2.8 macro lens on it, while the Digital Rebel had Canon's 18-55 f/3.5-5.6 zoom on it, set to a focal length of roughly 50mm. Both cameras were using 50mm macro lenses set to the closest macro focus (to fully blur the background), and were set to ISO 100, aperture priority mode with an aperture of f/36 (to produce a very narrow light cone, to resolve the dust specks) before pointing them at the (unfortunately rather cloudy) sky outside. The test aims to identify any dust on the sensor's surface, and if anything should favor the SD10 somewhat, since that camera has a dust cover and should only have whatever dust it left the factory with, where the Digital Rebel has no such cover and hence would have undoubtedly picked up some more dust while I've been using it since Canon shipped it to me. I'll leave it up to readers to decide how they think both cameras performed, but will say this - while the SD10 seems significantly better than the SD9 in this respect, I would still like to see a lot less dust inside a camera as it leaves the factory.
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