Utilizing the same DiGiC processor as other PowerShot digital cameras we have reviewed recently the A70's white balance performance came as no surprise. Automatic white balance works well under natural light and less so in incandescent or fluorescent lighting. As you can see from the samples below in incandescent light automatic white balance produced a strong orange cast. The pre-programmed presets work well as does manual preset white balance.
|Outdoors, Auto||Outdoors, Cloudy (or Sunny)||Outdoors, Manual|
|Incandescent, Auto||Incandescent, Incandescent||Incandescent, Manual|
|Fluorescent, Auto||Fluorescent, Fluorescent (or H)||Fluorescent, Manual|
The A70's closest macro performance as at wide angle, however for the best images with the least distortion and corner softness telephoto macro produced only slightly larger frame coverage. The macro tests below are using our new macro focus test chart and measurement system; each line on the grid is 10 mm, taken at shortest subject distance in macro mode.
|Wide angle - 62 mm x 47
33 px/mm (838 px/in)
Corner softness: Moderate
|Telephoto - 73 mm x 55
28 px/mm (711 px/in)
Corner softness: None
The A70's internal flash unit has a quoted range of 4.2 m at wide angle and 2.5 m at telephoto (Auto ISO). Our tests showed good color balance but underexposure (poor flash power metering) notably more on our 'normal' skin tone flash shot.
|Skin tone - Natural color, no blue cast, underexposed.||Color patches - Good color balance, no color cast, underexposed.|
The A70 has two methods available for night shots, the scene exposure mode 'Night Scene' and manual exposure. Night Scene is limited to a longest exposure of 1 second (which is honestly fairly useless for night exposures). Thus I chose to use manual exposure mode for the samples below. The A70 has automatic dark frame noise reduction for exposures of 1.3 seconds or longer. As you can see the A70 delivered clean noise free night exposures with surprising detail.
|Manual exposure: ISO 50, 4 sec, F4.0|
|Manual exposure: ISO 50, 15 sec, F8.0|
Barrel and Pincushion Distortion
The A70's exhibited 0.9% (below average) barrel distortion at wide angle but surprisingly also exhibited some (slight) barrel distortion at telephoto (0.3%). While not unheard-of it is unusual to see barrel distortion at the telephoto end of zoom, where we would expect either some pincushion distortion or no distortion at all.
|Barrel Distortion, 0.9% @ wide angle||Barrel Distortion, 0.3% @ telephoto|
Vignetting / Lens shading
Our vignetting / lens shading test is very simple, a shot
of a blank wall from two meters away, vignetting will always be most visible
at wide angle and maximum aperture and will start to disappear at smaller
apertures and/or further zoom. As you can see the A70's lens did produce
some slight shading at wide angle, noticeable mostly in the top right
and bottom right corners. To be honest this is far lower than most cameras
and would not be visible in every day shots.
|Very slight corner shading visible at wide angle and maximum aperture (F2.8)||No noticeable shading at telephoto (F4.9)|
Purple Fringing (Chromatic Aberrations)
Our CA test shot did appear to exhibit some fringing, however this is not the strong purple chromatic aberration fringing seen on other cameras, rather it is likely to be slight chromatic aberration amplified by blooming of the overexposed area of the image. In our everyday shots it was tough to find a clear example and even this wasn't objectionable or strong.
|Hard to find evidence of CA in everyday shots||Our standard chromatic aberration test shot|
Overall Image Quality / Specific Issues
For a three megapixel 'entry level' digital camera the PowerShot A70 really does deliver very good image quality. Images are well exposed with relatively good dynamic range, a normal Canon tone curve (lower contrast, more shadow detail) and natural but not under-saturated color response. Noise levels were low, especially at the ISO 50 setting and even at higher sensitivities noise is acceptable and increases predictably. Resolution is also very good, the A70 delivers about as much detail as we could expect from a three megapixel digital camera. From an image quality point of view the A70 does seem to be a bit of a bargain.
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