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 C-40Z features three selectable ISO sensitivities of 100, 200 and 400 as well as Auto mode which varies the sensitivity between ISO 100 and 200 depending on available light.
|Good light (10 EV)||Low light (3 EV)|
|ISO 100, 1/25 sec, F4.8||ISO 100, 1/2 sec, F3.4|
|ISO 200, 1/60 sec, F4.8||ISO 200, 1/5 sec, F3.4|
|ISO 400, 1/125 sec, F4.8||ISO 400, 1/10 sec, F3.4|
Interesting to note that the shutter speed difference between ISO 100 and ISO 200 is 1.3 EV not 1.0 EV, this indicates that the C-40Z's ISO 100 is probably closer to ISO 80. Noise is pretty much in line with what we've seen of other four megapixel digital cameras (although the C-40Z's ISO 100 (80?) is quite a bit cleaner than Canon's S-40 at ISO 100). Pretty much usable across the entire range.
Generally the C-40Z did a good job, it certainly put up a fight under artificial light, although still couldn't reach into the low Kelvin's under incandescent (or tungsten) lighting. Pre-programmed presets were all fairly good (except the fluorescent preset, at least under our bulb). I was a little disappointed to see that manual pre-setting of white balance under incandescent light produced a fairly nasty hue shift in all colours but blue (and more so for red).
|Outdoors, Auto||Outdoors, Sunny or Cloudy||Outdoors, Manual|
|Incandescent, Auto||Incandescent, Incan.||Incandescent, Manual|
|Fluorescent, Auto||Fluorescent, Fluorescent||Fluorescent, Manual|
Aperture Priority Mode
Aperture priority is where you designate the aperture and the camera calculates the best shutter speed, if the exposure is outside of the cameras range (either over or under exposing) the nearest shutter speed will display in red on the LCD screen. Used properly Aperture Priority can be invaluable as it has a direct effect on depth of field (the distance in front and behind the focal point which will be in focus when taking the shot).
The C-40Z has a limited range of selectable apertures:
- Wide: F2.8, F3.4, F4.0, F4.8, F5.6, F8.0
- Tele: F4.8, F5.6, F8.0
Aperture Priority is an exposure mode is accessed by turning the mode dial to A/S/M and selecting the 'A' option through the mode menu. You can change aperture by pressing the up or down arrow keys on the 4-way controller. A basic example of aperture priority is shown below for more read my digital photography glossary:
| F2.8, 1/60 sec
(Less depth of field)
|F8.0, 1/10 sec
(Most depth of field)
To sum up the C-40Z's macro performance I'd describe it as 'not bad, not fantastic', but better than some ultra-compact digital cameras. Optimum focal length was found at approximately half zoom where it's possible to get a frame coverage of approximately 7.5 cm (3 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 (35 mm)||F2.8||Too dark to measure (but not completely dark)|
|Telephoto (105 mm)||F4.8||3.2 EV (23 Lux / 2.1 foot-candle)|
Light intensity (Lux) = 2.5 x 2^EV (@ ISO 100), 10.76391 Lux = 1 foot-candle (fc)
For a camera without an AF-assist lamp the C-40Z does very well, it managed to continue focusing on our target as we dropped light levels below what our light meter can measure (time for a new light meter), although the camera couldn't focus in complete darkness. Of course, the story was different at the smaller aperture produced by zooming to telephoto, here we needed 3.2 EV of light (still quite dark).
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