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ISO Sensitivities & Noise

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 7i provides four selectable ISO equiv. sensitivities of ISO 100, 200, 400 and 800.

Note: At this stage we are not providing a direct comparison to another 5 megapixel digital camera because we intend to compare the 7i to Nikon's new Coolpix 5700 at a later date (review will be updated).

Each of the comparison crops below are made up of a 90 x 80 crop of patches 19, 22 and 24 of the ColorChcker chart (as indicated above). This helps to give a better impression of noise at different light levels within an image. Directly below this you will find the average standard deviation of these three patches, this is a quantifiable measurement of noise.

ISO 100
ISO 200
ISO 400
ISO 800

Although it's not completely apparent here noise levels even at ISO 100 are quite high.Higher than we would like to see from Minolta's flagship Prosumer digital camera. A more definitive test and comparison will be posted in this space at a later date.


White Balance

The DiMAGE 7i's automatic white balance was performed best under natural light, that said it did manage to do as well as pretty much any other digital camera under other types of light. The pre-programmed presets were also good, especially incandescent. Manual preset white balance almost always provided the most accurate and reliable colour balance.

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


Macro Focus

The DiMAGE 7i now has two zoom positions for macro focus. The first is at full wide angle (28 mm equiv.) the second is at or near full telephoto (approx. 175 - 200 mm). I was curious to see why Minolta chose to add the wide angle macro option, and the results were disappointing.

Macro Focus: Wide angle

As you can see the wide angle macro focus option provides very little in the way of macro ability. The only thing it does allow for are very close focus distances at the wide angle setting. This could potentially be used to capture a near object in the foreground of a landscape shot.

Macro Focus: Telephoto

Macro focus at telephoto is considerably better. It requires you to have the camera some distance from the subject, but that in itself can make lighting easier. The optimum frame coverage was achieved at full telephoto (200 mm equiv.) and was approximately 55 mm (2.2 in).


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 Lowest light focus
Wide angle (28 mm) F2.8 -1.5 EV (0.9 Lux / 0.08 foot-candle)
Telephoto (200 mm) F4.8 -0.8 EV (1.4 Lux / 0.13 foot-candle)

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

A simply brilliant performance for a digital camera without an AF assist lamp. The DiMAGE 7i's unique ability to switch CCD output to a high sensitivity black and white mode means that the contrast detect AF system can continue to work at low light levels which would be beyond any other non-AF-lamp digital camera. Kudos.


Pop-up Flash Performance

The DiMAGE 7i's pop-up flash has a specified range of approximately 0.5 - 3.8 m (1.6 - 12.5 ft) at wide angle and 0.5 - 3 m (1.6 - 9.8 ft) and telephoto. Generally speaking it performed well, skin tones were natural without any visible colour cast. Flash exposures were well exposed and coverage was as good as we would expect considering the 7i's wide 28 mm bottom end.

Skin tone test: Good exposure, well metered and good colour, no cast. Wall test: 2m: Good exposure with some drop off in the bottom corners. Color patch test: Good exposure, well metered with good colour.
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