Noise, Noise, Noise: Three Canon SDs put to the test

As consumers, we tend to buy in to the idea that technology marches forward, offering substantive improvements across the board from one generation of device to the next. As savvy digicam users, however, we also know that newer doesn't always mean better where high-ISO noise control is concerned. Ever-increasing sensor resolution without directly corresponding increases in physical sensor size has been to blame for the current crop of top-of-the-line 12 megapixel compact cameras that many feel are noisier than ever.

Tech heads (and I'll include myself on this one) like to make a lot of noise about noise, spending countless hours studying high-ISO images at improbably high enlargements to make pronouncements about camera performance. Doing this very thing with the control shots for our currently in-process Canon SD890 IS review, though, I started thinking: is this perception that higher-res cameras don't, as a rule, perform as well at higher ISOs all just that – a perception? How would the 10 megapixel SD890 stack up against the 12 megapixel SD950? What about against the two-year-old, 6 megapixel SD700?

With all three cameras at my disposal, these questions are easy enough to answer...

THE CONTENDERS

The grandfather of this bunch is the Canon PowerShot SD700 IS. One of the earliest Digital ELPH cameras to offer image stabilization, the 6 megapixel SD700 features a 4x (35-140mm) lens that's been a repeat performer in Canon's SD line over the years.

(view large image)

The SD700 features a sensitivity range of ISO 50 to ISO 800 – making the older SD seem a little bit limited in a world where ISO 1600 has become commonplace. In its defense, for a digicam the SD700 is getting up there in years: like your housepets, digital cameras age faster than humans, with the SD700's 2006 birthday putting the camera's "actual" age somewhere around 60 – if it's not quite what I'd call old, it's definitely thinking about retirement, at least.

Our mid-res competitor, the Canon PowerShot SD890 IS, is the stylistic and functional progeny of the SD700. It touts a longer lens, a sharper screen, and more resolution (10 megapixels) on a slightly larger sensor (1/2.3-inch, versus the SD700's 1/2.5-inch unit).

(view large image)

Compared to the SD700, the brand-spanking-new SD890 technically loses sensitivity at one end of the range in exchange for more power at the other, with effective ISO options between 80 and 1600.

If you like things that are expensive just to be expensive, you might well already own the 12.1 megapixel, titanium encased Canon Powershot SD950 IS.

(view large image)

The top-of-the-line SD model came to the market nearly a year ago with a $400+ asking price. While it doesn't offer much that really stands out in the way of zoom or LCD improvements (if anything, the lens is the least versatile in this group), the SD950 uses a 1/1.7-inch CCD sensor – notably larger than those used in the other two cameras. At full resolution, sensitivity range is the same as the SD890's: 80 to 1600.

THE TEST

Getting a baseline image for comparison wasn't difficult, as it's part of our regular camera test procedures: for noise evaluation purposes, we use a 350-pixel detail crop from a controlled still-life shot.

Of course, comparisons between all three cameras can't be made at all sensitivity settings, given that the SD700 lacks an ISO 1600 option. Likewise, while the crops are all taken from the same area of the image, differences in total image size (each camera was set to its maximum possible resolution and highest JPEG quality setting) translate to differences in the exact amount of detail captured in each crop. This, in turn, ultimately has an impact on how much detail loss impacts a fixed size print, an idea that I'll touch on more momentarily.

THE RESULTS

Side-by-side crops for the SD700 versus the SD890 are as follows:

Comparing these two cameras, the advantages not only of more resolution, but also of improved sensor and processing technology become apparent. There's slightly less noise at ISO 800 with the SD890, especially in the dark blue field areas, and nearly twice as much resolution allows for a lot more detail capture (and thus, somewhat more detail preservation) at high ISOs. And perhaps obviously, if you need to shoot at ISO 1600, there's only one camera among these two that's up to the task.

Compared to the SD890, the SD950 looks like this:

Closer resolution in this case means detail capture is much closer between these two. That said, there's a noticeable difference in the sharpness of fine lines from about ISO 200 on. Even with its resolution advantage, the SD950 simply doesn't hold on to the crispness seen in the SD890 at ISO 800 and 1600. While there's not a significant noise increase with the SD950 (thank a larger sensor for that, I'd imagine), the obvious advantage of higher-res cameras – more resolved detail, which is the very definition of resolution – isn't, in fact, an advantage at all in this case.

Out of all of this, a few general conclusions can be drawn. First, in printing the full-size ISO 800 images from all three cameras at 5x7 inches, I had a lot of trouble telling the difference between them. All three were a little soft, but even with the SD700's 6 megapixel image, a fair amount of downscaling was used to get a 300 dpi print at this size. Likewise, for the slightly soft SD950, especially, this – the ability to downscale, and thus mask detail loss – is one of the often overlooked benefits of more pixels where noise control for prints is concerned.

Equally interesting was the fact that the difference between ISO 800 prints and ISO 50/80 prints at this size were also largely indistinguishable, with a little bit of softness and some very slight patterning in solid-color areas giving away the high-sensitivity shots only under close inspection.

At 8x10 and ISO 800 things get a little more distinct, with the SD700 pushing beyond the limits of its resolution at 300 dpi. Still, the SD950's slight resolution advantage over the SD890 continues to mask its slightly weaker performance.

CONCLUSIONS

In some ways, then, supposed improvements of newer technology were borne out in this particular case, at least. Under detailed analysis, the SD890 shows well-controlled noise and detail loss across the board – better than the lower-res SD700, and better than the SD950 with its larger sensor. Conversely, at ISO 800 (the highest sensitivity common to all three cameras), the difference in even a 5x7 print was almost impossible to make out, and at 8x10, the current-generation SD cameras are still neck and neck.

The overarching suggestion of this test, then, has to do at least as much with our arguably undue hang-up with sensor noise. While the SDs used for this test may perform somewhat better than average in this area, comparing ISO 80 versus ISO 800 prints from this test only further reinforces the idea that unless you're making bigger enlargements than most of us (come on: be honest) usually make or have an unusually noisy camera, make sure you've actually given test printing your results (and not just looking at generally ugly 100-percent views on-screen) before determing that your cam doesn't have the horespower to keep up at higher ISOs.

As is often the case, the results may surprise you.