Sony Cyber-shot DSC-R1Sony "breaks the mold" with a unique SLR/all-in-one hybrid design.<<User Report :(Previous) | (Next): Design>> Page 3:Technology NotesReview First Posted: 09/20/2005, Updated: 11/18/2005 |
Technology Notes
By Dave Etchells
As you may have gathered from Shawn's User Report above, the Sony DSC-R1 is an unusual beast in a number of areas, as it incorporates a few technological twists not found in any other digital camera currently on the market. There's enough that's new here to deserve some separate attention to the technology itself. Here are our notes on a few of the developments embodied in the R1:
Big Sensor + Live Viewfinder
Clearly, the heart of the Sony DSC-R1 story is that it combines a slightly less than APS-C sized image sensor with a live LCD viewfinder display. The larger physical pixel dimensions made possible by larger image sensors lead to improved light sensitivity and lower image noise levels, while the live LCD viewfinder carries the usual benefits of precise framing, the ability to preview white balance and exposure, and flexible shooting angles. The sensor in the DSC-R1 is the same size as those found in a majority of digital SLRs currently on the market, and its ISO and noise performance are at least in the same category as those cameras. The illustration below shows the difference between the sensor used in Sony's earlier DSC-F828 and that used in the R1.
As image sensors become larger and larger, it takes more and more power to clock the data off the array. This isn't a problem when you're only concerned about reading out the image data two or three times a second, but keeping an LCD viewfinder truly "live" means clocking the data off at least fifteen times a second, preferably even more. With an ordinary CCD imager the size of the one in the Sony DSC-R1, this would require a couple of watts of power, about half the amount required to power a typical household night-light. A bit much for a digital camera, to say the least.
On the DSC-R1, Sony is using CMOS sensor technology to beat the power problem. CMOS sensors in general require less power to read data out of the array, and some designs also permit some level of random access to the pixels, further reducing power requirements. In the R1's chip, Sony has apparently worked some electronic magic to reduce the power levels below what even conventional CMOS imagers would require. Comparing the R1 to the earlier DSC-F828 , total power associated with image readout (driver circuitry, the sensor chip itself, and the output sample/hold circuit) has been reduced from 0.75 watts to only 0.2 watts, even while the array size has been considerably increased. Besides making the live LCD viewfinder possible, this also contributes to improved battery life overall.
While the through-the-lens optical viewfinders of digital SLRs provide accurate framing and generally better low-light usability than electronic viewfinders, they can't show exposure or white balance effects the way an LCD can. As alluded to above, the R1's tilt-swivel LCD also greatly facilitates overhead or ground-level shooting. When it comes to low light shooting, the live viewfinder on the Sony DSC-R1 does better than most when faced with dim surroundings, but still doesn't work down to as low a light level as is possible with a human eye behind a typical optical viewfinder eyepiece. Overall though, the R1's combo of live LCD display and near-APS-C sensor size is quite an accomplishment, and opens the door to other camera improvements as well.
Closing out the discussion of the Sony R1's huge image sensor though, there's one very typical all-in-one digicam feature that's missing: Movie capture. Apparently the large sensor size just doesn't permit rapid enough readout or data processing to provide a movie mode. That's a shame, as movie capability is one of the key advantages of all-in-one digital camera designs over the d-SLR format, and a feature that's increasingly popular with consumers.
Optics: Short Back-Focus
While a live LCD viewfinder display is a nice feature, it's actually not the biggest benefit of the Sony DSC-R1's design. It turns out that eliminating the large mirror box required in digital SLRs conveys huge optical benefits to the lens system. What's involved is reducing the "back-focus distance" of the lens, which makes it much easier to reduce chromatic aberration and other optical defects. The illustration at right shows a cutaway view of a typical digital SLR. The green arrow highlights the distance between the rear lens element and the sensor surface. (Image courtesy Sony corporation.)
As noted, back-focus is basically the distance between the rear element of the lens and the surface of the imager, and has much to do with how difficult it is to engineer the lens system for low chromatic aberration and other distortions. One way to understand this is to consider that the lens has to "project" the image across the gap between the back of the lens and the sensor itself. It makes sense that the smaller this distance, the more accurate the "projection" would be.
In a conventional SLR, the minimum back-focus distance is set by the space required for the rotating mirror assembly. SLRs built on conventional 35mm bodies typically have back-focus distances of 30mm or more, while special digital-specific lenses (like Canon's EF-S series) have back-focuses of about 20mm. By contrast, the R1's optical system has a back-focus distance of only 2.1mm. This should translate into noticeably lower chromatic aberration at wide angle focal lengths, and in fact, we saw very little chromatic aberration with the R1 our test shots. (There was a small amount of chromatic aberration present, but it was quite a bit less than we'd normally expect on a high-end "prosumer" digital camera.) The DSC-R1's lens also showed considerably better corner sharpness than we're accustomed to seeing from cameras anywhere close to its price range.
The excellent optical quality of its lens does a lot to shore up the Sony DSC-R1's competitive position relative to removable-lens digital SLRs: While you can get a very nice d-SLR with lens for about what you'll have to pay for the Sony R1, you'd have to shell out a lot of cash to match its combination of focal length range and genuinely excellent optical quality. (You could easily pay more than the cost of the entire R1, just for a lens or pair of lenses to equal its optical capability and quality.)
Color Rendering: "Vivid" mode
Most cameras have a color mode that boosts color saturation. Here again though, Sony's briefing materials called special attention to the "Vivid" mode on the DSC-R1. The briefing document seemed to focus on "depth of sky" (deeper, richer hues in sky colors) as the primary intent of Vivid mode, and it does appear to emphasize and deepen blues a fair bit. Overall though, Vivid mode appears to emphasize all the additive primary colors (reds, greens, and blues) about equally, leaving purples, some cyans, and yellows more or less untouched.
Color saturation is a pretty subjective thing, with different people having widely varying preferences. - So there'll likely be a wide range of reaction to Vivid mode on the Sony DSC-R1. We personally tend not to be big fans of highly saturated color, so ourselves much prefer the R1's Standard color rendering. Fans of bright, saturated color may well love it though.
A.G.C.S. - Advanced Gradation Control System
Because the range of brightness in the natural world is so much greater than can be properly shown on a CRT or a print, a perpetual challenge for photographic systems has been how to make the best use of the limited tonal range they have to work with. This problem can be particularly acute with digital cameras, most of which tend to expose like slide film, easily losing highlight detail, and plugging shadows. Many digital cameras have contrast adjustments that let you make fairly coarse adjustments to their tone curves, but the results are often hit or miss, as they're made without reference to the actual image itself.
The Sony DSC-R1 introduces a new technology that Sony has dubbed the Advanced Gradation Control System (AGCS for short). More than just a contrast adjustment, AGCS analyzes the tonal distribution of the scene (the intensity histogram), and then stretches or compresses the tonal scale as needed to make best use of the total tonal range. The action taken depends on the particular scene being shot: A low contrast subject will have its tonal scale stretched (increasing contrast), while a subject with a very wide tonal range (such as a backlit subject) will have its tonal range compressed. Because it's histogram based, AGCS should do better dealing with different parts of the tonal scale in the same image: Duller highlights may be pushed higher up the tone scale and somewhat compressed, while dark shadows will also be pulled up the tonal scale, but have their tonal range expanded.
In our own test shooting with the DSC-R1, the effects of AGCS were very subtle, to the point that we could only see its operation clearly on a single image. We had hoped that this function would get tweaked a bit as the camera moved from prototype to full production, but that doesn't appear to be the case: AGCS produces only very subtle effects under most shooting conditions where we would expect it to apply. The concept of AGCS is an excellent one, but it needs to be tweaked a little more, to have a greater impact on typical subjects.
Technology Summary
While a tweaked "vivid" mode will appeal to some users, and A.G.C.S seems to hold some nice potential, the big story with the Sony DSC-R1 is its combination of large sensor and live LCD viewfinder, and most particularly what that combination did for the overall optical design. See below to see a sample of what the R1's optical system can do.
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