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ISO (Sensitivity) Adjustment

ISO equivalence on a digital camera is the ability to increase the sensitivity of the CCD to allow for faster shutter speeds and/or better performance in low light. The way this works in a digital camera is by "turning up the volume" on the CCD's signal amplifiers, nothing is without its price however and doing so also amplifies any noise that may be present and often affects colour saturation.

The Sony DSC-P9 provides an Auto ISO sensitivity mode which varies sensitivity between ISO 100 and 320 depending on light levels. In addition you can also manually select ISO sensitivity of 100, 200 or 400. The samples below are 100% crops from patches on a GretagMacBeth ColorChecker shot at different sensitivities with both the Sony DSC-P9 and (for comparison) a Canon PowerShot S40. Note that although the P9 doesn't support ISO 50 I have included the S40's ISO patch crops for reference purposes.

ISO 50 Sony DSC-P9 Canon PowerShot S40
n/a 1/13 sec, F4.5
ISO 100 Sony DSC-P9 Canon PowerShot S40
1/15 sec, F4.5 1/25 sec, F4.5
ISO 200 Sony DSC-P9 Canon PowerShot S40
1/30 sec, F4.5 1/50 sec, F4.5
ISO 400 Sony DSC-P9 Canon PowerShot S40
1/60 sec, F4.5 1/100 sec, F4.5

What's initially worth noting is how much "more sensitive" the S40's exposures are at the same ISO sensitivity. This is yet another example of how much difference there can be between one manufacturers interpretation of ISO 100 and the next. Indeed, at each sensitivity the S40 was able to achieve two thirds of a stop faster shutter speeds. Using a light meter it was easy to ascertain that the the P9's ISO sensitivities are accurate and that the S40's are about 0.7 EV more sensitive than described (ISO 50 = ISO 80, etc.)

With this in mind we can see that at the same "sensitivity" noise levels between the two cameras are virtually identical. Overall the S40 comes out on top with its additional ISO 50 and the fact that it's sensitivities appear to be almost a stop faster than the P9.


White Balance

The DSC-P9 is part of a new line of Sony digital cameras which finally offer us a good range of white balance options. At this level there's no manual preset white balance but we do get the full range of Auto, Daylight, Cloudy, Tungsten and Fluorescent. The results are mixed, under natural light the Daylight / Cloudy options provide a useful way to 'lock' the white balance (although Auto had always been fairly good under natural light). Overall these new pre-programmed settings worked fairly well, white balance presets for Incandescent and Fluorescent light both worked well (an area where most digital cameras trip up). Kudos Sony.

Outdoors, Auto Outdoors, Cloudy Outdoors, Daylight
 
Incandescent, Auto Incandescent, Incandescent  
 
Fluorescent, Auto Fluorescent, Fluorescent  


Low Light Focus

This test measures the minimum amount of light under which the camera can still focus. The focus target is our lens distortion test chart (shown here on the right), camera is positioned exactly 2 m (6.6 ft) away.

Light levels are gradually dropped until the camera can no longer focus. This is carried out at both wide angle and telephoto zoom positions (as more light reaches the focusing systems with a larger aperture).

This test target is the optimum type of subject for most "contrast detect" AF systems (as it has a vertical line at its center), you should consider the results below the best you could expect to achieve.

Lens position Aperture AF Assist lamp Lowest light focus
Wide angle (39 mm) F2.8 On Complete darkness
Telephoto (117 mm) F5.6 On Complete darkness
Wide angle (39 mm) F2.8 Off 0.9 EV (4.7 Lux, 0.4 fc)
Telephoto (117 mm) F5.6 Off 2.3 EV (12.3 Lux, 1.1 fc)

Light intensity (Lux) = 2.5 x 2^EV (@ ISO 100), 10.76391 Lux = 1 foot-candle (fc)

The DSC-P9's AF assist lamp is a very powerful orange bulb type, it manages to light the scene (even at fairly long distances) in complete darkness and achieve good first-time AF locks. Without the lamp the DSC-P9 can still focus at very low light levels at wide angle, but as we'd expect needs a little more light at full telephoto.


Flash Performance

Compared to the DSC-P5 the P9 boasts an extended flash range of 0.5 - 3.8 m (1.8 - 12.5 ft). It appears to achieve this additional range by utilizing Auto ISO and increasing sensitivity to ensure that flash power is sufficient to light the entire subject.

Sony have recently been plagued with "Blue Flash Syndrome" (certain types of flash shots having a strong blue cast), this has affected several of their models. The DSC-P9 does appear to have partially escaped, although it was clear that flash white balance was a little inconsistant (see two hand shots one after another).


Barrel and Pincushion Distortion

Virtually no measurable pincushion distortion at full telephoto (very good) but somewhere between 1.1 and 1.2% barrel distortion at wide angle. This wide angle barrel distortion is about what we'd expect for an ultra-compact extending lens system as used on the DSC-P9.

Barrel Distortion, 1.2% @ wide angle Pincushion Distortion, 0% @ telephoto


Purple Fringing (Chromatic Aberrations)

Although the DSC-P9 does exhibit very slight purple fringing, it's definitely at the bottom end of the scale. Pretty much in line with what we've seen from the DSC-P1 and P5. There was also a certain amount of blooming around overexposed areas of an image.

Example of chromatic aberrations in an "every day" shot
Our now standard chromatic aberration test shot - visible chromatic aberrations.


Overall Image Quality / Specific Issues

Sony appear to be taking a more cautious approach to colour these days. The DSC-P9 exhibits good, neutral colour balance. Colours are good and accurate but are generally not over-saturated (a complaint many have had of previous Sony digital cameras). Overall image quality is good, especially considering the camera's small proportions.

Ghosting / Blooming

Images taken at either maximum (F2.8 at wide angle, F5.6 at telephoto) or slightly smaller apertures did suffer from a certain amount of ghosting (blooming?) around bright / over-exposed areas of the image. This appears as a halo around the bright area, as you can see in the two examples below. While not a major issue and isolated to a few shots it is worth noting.

White ghosting visible around the white body of the pelicans
Yellow ghosting visible around the bright (over-exposed) yellow sunflowers
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