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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 DiMAGE S304 has four selectable ISO sensitivities of 100, 200, 400 and 800 as well Auto mode which varies sensitivity between ISO 100 and 200 automatically depending on available light. Test images shot under both good and low light.

Good Light (11 EV) Low Light (3 EV)
ISO 100, 1/30 s, F4.8 ISO 100, 1.4 s, F4.8
ISO 200, 1/60 s, F4.8 ISO 200, 1 s, F4.8
ISO 400, 1/125 s, F4.8 ISO 400, 1/3 s, F4.8
ISO 800, 1/362 s, F4.8 ISO 800, 1/8 s, F4.8

Although there is some noise visible at ISO 100 it's no worse than we've seen of most 3 megapixel digital cameras, an indeed its better than some. Above this ISO 200 and 400 are both usable, on the understanding that there will be some noise. ISO 800 could be useful when you need high shutter speeds and will be reducing the resulting image in size.


White Balance

Clearly the S304's automatic white balance is tuned to natural light, which is logical as this is where the majority of shots will be taken. The pre-programmed settings worked fairly well, especially for incandescent light. The manual preset option produced consistent and accurate white balance.

Images re-saved to sRGB colour space [info]

Outdoors, Auto Outdoors, Cloudy (or Daylight) Outdoors, Manual
Incandescent, Auto Incandescent, Incandescent Incandescent, Manual
Fluorescent, Auto Fluorescent, Fluorescent Fluorescent, Manual

First word indicates the light in whcih the shot was taken, the second indicates the selected white balance mode.


Aperture Priority

The S304 only has two apertures: F3.0/F6.7 at wide angle and F3.6/F8.0 at telephoto. The example below was shot in aperture priority mode combined with macro focus (focal length locked at approximately 75 mm; 2x). As you can see there is more depth of field with the aperture set to its closed position (F6.0) but that it doesn't afford you as much control as on other 'prosumer' digital cameras.

Images re-saved to sRGB colour space [info]

F3.5, 1/60 sec F6.0, 1/15 sec


Macro Focus

The S304's macro mode would probably be better described as 'close up', it does allow closer subject distance than normal focus but doesn't get in close enough to give you a 'macro' frame coverage. Switching to Macro mode fixes the focal length at approximately 75 mm (2x), the minimum focus distance is 16 cm (6.3 in) from the lens. This gives a horizontal frame coverage of 7.5 cm (3 in).

Images re-saved to sRGB colour space [info]


Low Light Focus

In a new addition to our reviews we'll now be measuring 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 Lowest light focus
Wide angle (35 mm) F3.0 1.5 EV (7.1 Lux / 0.7 foot-candle)
Telephoto (140 mm) F3.6 2.3 EV (12.3 Lux / 1.1 foot-candle)

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

Despite the S304's F3.0 maximum aperture it still manages to catch the focus down to 1.5 EV, in low light the camera increases the CCD's sensitivity to maintain the LCD image, eventually turning it black and white when things get really dark. At the telephoto end the maximum aperture is approximatey three quarters of a stop smaller and so it's no surprise that we need roughly that much more light to focus. Remember these values are the best you could expect given a high contrast subject.

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