Canon PowerShot A720 IS Concise Review
With tiny, high pixel count chips noise is always going to be an issue, and to a large degree this is more a test of the effectiveness (both measurable and visible) of a camera's noise reduction system. Designers have to balance the desire to produce smooth, clean results with the need to retain as much detail as possible (if you blur away the noise, you blur away image detail too). The gray panels clearly show that noise is pretty well controlled until ISO 800, at which point it rapidly becomes unmanageable. However, looking at the stamp crops below, it can be seen that a lot of detail as been blurred away by ISO 400. ISO 800 is just about usable for small prints, something it's a lot harder to say for ISO 1600, which is firmly in the 'emergency use only' camp.
|ISO 80||ISO 100||ISO 200||ISO 400||ISO 800||ISO 1600|
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity is on the vertical axis.
As is pretty standard with modern compacts, noise starts to become visible at around ISO 200. Above this point, both noise and the loss of contrast and detail that come from noise reduction become noticeable. Adding an ISO 1600 mode to a camera that is desperately struggling at ISO 800 seems pretty hard to justify but most camera manufacturers are doing it, so Canon is no more to blame than anyone else. As we so often find ourselves saying: ISO 1600 is really only for emergencies. It's interesting to note that we couldn't get AUTO HI ISO mode to use ISO 1600, suggesting the camera designers aren't that impressed with the results either.
Low contrast detail
What the crops and graph don't show is the effect of noise reduction on low contrast fine detail such as hair, fur or foliage. An inevitable side effect of noise removal is that this kind of detail is also blurred or smeared, resulting in a loss of 'texture'. In this test the crops below show the effect of the noise reduction on such texture (fur) as you move up the ISO range.
|ISO 80||ISO 100||ISO 200|
|ISO 400||ISO 800||ISO 1600|
As the crops above show, at the lowest two ISO settings, the A720 IS does a good job of retaining information and differentiating between very subtle texture differences. This precision is dulled a little at ISO 200, in which the contrast starts to drop. The results are still very good, though. At ISO 400 the process continues and, this time, the level of detail visibly suffers (though it's a lot better than many of its competitors). ISO 800 doesn't do a terribly good job of differentiating between tones, smoothing away much of the texture and introducing aberrant color. And ISO 1600, as with just about every other small-sensor camera, is pretty terrible. Chroma noise and odd noise-reduction artefacts are easier to spot than the fine detail present in the scene.
Optical image stabilization
The A720 IS offers three IS modes: Continuous (IS on all the time), 'Shoot only' (IS is activated at the moment the exposure is made) and Panning (IS only compensates for vertical movement for when panning horizontally). The first option makes framing easier - the IS system steadies the preview image - but the second is easier on the batteries and supposedly more effective. With its 35-210mm equivalent lens you would reasonably expect to be able to get steady shots at 1/40th of a second at the wide end of the lens and 1/200th at the long end without the aid of IS.
We tested the IS system at the long end of the zoom and found that, with it turned off, sharp images could not be guaranteed at 1/125th sec or slower (Which the camera accurately reflects by displaying a camera shake warning). With IS set to continuous, 80% of the shots were sharp at 1/50 sec and 60% when the camera shake warning arrives at 1/30. With IS set to "shoot only," 90% of shots are still sharp at 1/30th, two stops slower than was possible hand-held. This is really very reasonable performance and shows the benefit of using a lens-shift anti-shake system at a price point that sees some competitors resorting to electronic (post-processing) methods.
|IS OFF||IS Continuous mode||IS Shoot Only mode|
At the wide end of things, we'd expect to be able to handhold without IS down to about 1/40th and, sure enough, we found we got 90% perfectly sharp (again the shake warning comes on at this speed). Less than half the shots were sharp by 1/15th. Turning IS onto "Shoot Only" mode gives sharp shots 90% of the time down to 1/15th (at which point the shake warning appears), and maintains a 50% hit rate as low as 1/10th. This suggests the IS is only offering about a one stop advantage when the lens is zoomed out.
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