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 E-20 features three selectable ISO sensitivities of 80, 160 and 320 as well as Auto mode which varies the sensitivity depending on available light.

I decided to use the same system created for our EOS-1D preview. This involves shooting our standard colour patches in average light (9 EV) at the full range of ISO sensitivities.

Each of the comparison crops below are made up of a 100 x 80 crop of patch 1, 7 (M) and 17 of the greyscale of our colour patches (as shown on the right). 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.

Camera	Olympus E-20	Sony DSC-F707
Sensitivity	ISO 80	ISO 100
Exposure	1/8 s, F4.5	1/10 s, F4.5
Patch crops
Std dev.	1.82	1.43
Camera	Olympus E-20	Sony DSC-F707
Sensitivity	ISO 160	ISO 200
Exposure	1/15 s, F4.5	1/20 s, F4.5
Patch crops
Std dev.	2.08	2.18
Camera	Olympus E-20	Sony DSC-F707
Sensitivity	ISO 320	ISO 400
Exposure	1/30 s, F4.5	1/30 s, F4.5
Patch crops
Std dev.	2.51	2.30

As you can see visually there is not a huge difference between the two, both exhibit some visible noise at ISO 100 (ISO 80 on E20) and things become much closer at ISO 200 (ISO 160 on the E20). Overall this is about what we'd expect from a newer prosumer level digital camera.

For a further comparison of the Olympus E-20's noise levels please see our Nikon Coolpix 5000 review.

White Balance

Overall the E-20's automatic white balance functioned very similarly to many other prosumer digital cameras, good in natural light and less good in artificial. That said it does have one of the widest range of pre-programmed white balance settings (each marked with their Kelvin temperature) which did seem to work very well (in many cases better than manual preset).

Manual preset on the E-20 is very easy, just press the button on the front of the camera and it will instantly take a reading. While this worked well in daylight or strong shade it did appear to produce a hue shift in reds under incandescent light.

Outdoors, Auto	Outdoors, 6500K / 5500K	Outdoors, Manual
Incandescent, Auto	Incandescent, 3000K / 3700K	Incandescent, Manual
Fluorescent, Auto	Fluorescent, 4000K / 4500K	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).

Thanks to its bright lens the E-20 provides a wide range of apertures between F2.0 (at wide angle, F2.4 at telephoto) and F11. While this will seem limited to conventional 35 mm SLR users it's at least two stops more than most consumer digital cameras.

• Wide: F2.0, F2.2, F2.4, F2.8, F3.2, F3.6, F4.0, F4.5, F5.0, F5.6, F6.3, F7.1, F8.0, F9.0, F10.0, F11.0
• Tele: F2.4, F2.8, F3.2, F3.6, F4.0, F4.5, F5.0, F5.6, F6.3, F7.1, F8.0, F9.0, F10.0, F11.0

Aperture Priority is an exposure mode is accessed by turning the mode dial to A. You can change aperture by rolling the main or sub dial. A basic example of aperture priority is shown below for more read my digital photography glossary:

F2.2, 1/50 sec (Narrow depth of field)	F11.0, 1/2 sec (Most depth of field)

Macro Focus

The E-20's native macro ability could be described as 'above average', switch into macro mode and use manual focus (it's easier to lock to the minimum possible focus distance) and you can use the entire zoom range, the best coverage (without distortion) was found at full telephoto. This produced a closest coverage of approximately 73 mm (2.9 inches) across the frame.

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.

Inconsistent results

Despite my best efforts the E-20 produced inconsistent results in low light. Its secondary infrared focusing system appeared to be able to work even in complete darkness, but not all the time. I ended up having to change the parameters of this test to produce some meaningful figures.

Instead of a single test I ran three tests at different light levels. At each light level I took 5 shots at wide angle and 5 shots at telephoto, for each shot I made sure that the AF system was sure of a lock (the dot indicator in the viewfinder was solid, not blinking). This test produced the following results:

• In complete darkness
  • Wide angle: 3 out of 5 shots were in focus
  • Telephoto: 1 out of 5 shots were in focus
     
• In 3 EV of light (20 Lux / 1.9 foot-candle)
  • Wide angle: 3 out of 5 were in focus
  • Telephoto: 3 out of 5 were in focus
     
• In 5 EV of light (80 Lux / 7.4 foot-candle)
  • Wide angle: 5 out of 5 were in focus
  • Telephoto: 5 out of 5 were in focus

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

As you can see the E-20's AF system proved to be unreliable in low light and better as light levels increased, what's a little more worrying is the fact that the camera was 'convinced' it had a good focus lock, examining the images later it was clear that it had not.