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ISO / Sensitivity accuracy

In a new addition to our reviews we are now measuring the actual sensitivity of each indicated ISO sensitivity. This is achieved using the same shots as are used to measure ISO noise levels, we simply compare the exposure for each shot to the metered light level (using Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV.

As you can see the Olympus E-500 and E-300 metered the same exposures which matched the metered exposure as-good-as exactly, the Canon EOS 350D (Digital Rebel XT) proved to be about a third of a stop more sensitive than indicated.

Indicated
sensitivity
Olympus E-500
(actual sensitivity)
Olympus E-300
(actual sensitivity)
Canon EOS 350D
(actual sensitivity)
ISO 100 ISO 100 ISO 100 ISO 125
ISO 200 ISO 200 ISO 200 ISO 250
ISO 400 ISO 400 ISO 400 ISO 500
ISO 800 ISO 800 ISO 800 ISO 1000
ISO 1600 ISO 1600 ISO 1600 ISO 2000

ISO / Sensitivity noise levels

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. The works by turning up the "volume" (gain) on the sensor's signal amplifiers (remember the sensor is an analogue device). By amplifying the signal you also amplify the noise which becomes more visible at higher ISO's. Many modern cameras also employ noise reduction and / or sharpness reduction at higher sensitivities.

To measure noise levels we take a sequence of images of a GretagMacBeth ColorChecker chart (controlled artificial daylight lighting). The exposure is matched to the ISO (ie. ISO 200, 1/200 sec for consistency of exposure between cameras). The image sequence is run through our own proprietary noise measurement tool (version 1.4 in this review). Click here for more information. (Note that noise values indicated on the graphs here can not be compared to those in other reviews). Room temperature is approximately 22°C (~72°F), lighting simulated daylight.

E-500 Noise Filter option

When we were first introduced to the E-500 we were fairly excited to hear that Olympus were including a user controlled 'Noise Filter' designed to deal with high ISO noise. This however turned to disappointment when we realized that there are in fact only two levels of noise filter, the default (when ISO boost is set to 'ON') equating to 'Some', the additional option (when ISO boost is set to 'ON+NF') equating to 'Some more'. It would have been nice to have a full range of NF levels to choose from. As you can see from the comparison below the default is already applying quite a bit of noise reduction (more than the E-300), enough to soften the image, so my preference is to leave the additional NF option switched off.

Olympus E-300 vs. E-500 (Noise Filter comparison only)

Olympus E-300
ISO 400
Olympus E-500
ISO 400
Olympus E-500 NF
ISO 400
Olympus E-300
ISO 800
Olympus E-500
ISO 800
Olympus E-500 NF
ISO 800
Olympus E-300
ISO 1600
Olympus E-500
ISO 1600
Olympus E-500 NF
ISO 1600

As mentioned above the additional 'NF' option doesn't suddenly make the image look 'cleaner' than with it switched off. What it does appear to do is reduce the visibility of chroma noise (colored blobs for want of a better description). Compared to the E-300 however the E-500's crops look cleaner but at the expense of detail, with the E-500's detail crops looking noticeable softer and more 'blurred' than the E-300.

Olympus E-500 vs. Canon EOS 350D (Digital Rebel XT) vs. Olympus E-300

For the reasons demonstrated above we chose to use the 'ISO Boost: On' option which applies the lowest level of noise reduction for the comparison below, primarily because the 'On+NF' option doesn't visually reduce noise that much more but does soften the image even further.

  • Olympus E-500: Olympus 50 mm F2.0 Macro lens, Aperture Priority (F3.5), Manual WB,
    Default Parameters, JPEG Large / Fine, ISO Boost: On
     
  • Canon EOS 350D: Canon 50 mm F1.4 lens, Aperture Priority (F4), Manual WB,
    Parameters 1 (default), 50 mm F1.4, JPEG Large / Fine
     
  • Olympus E-300: Olympus 50 mm F2.0 Macro lens, Aperture Priority (F3.5), Manual WB,
    Default Parameters, JPEG Large / Fine
Olympus E-500
ISO 100
Canon EOS 350D
ISO 100
(125 equiv.)
Olympus E-300
ISO 100
Olympus E-500
ISO 200
Canon EOS 350D
ISO 200
(250 equiv.)
Olympus E-300
ISO 200
Olympus E-500
ISO 400
Canon EOS 350D
ISO 400
(500 equiv.)
Olympus E-300
ISO 400
Olympus E-500
ISO 800
Canon EOS 350D
ISO 800
(1000 equiv.)
Olympus E-300
ISO 800
Olympus E-500
ISO 1600
Canon EOS 350D
ISO 1600
(2000 equiv.)
Olympus E-300
ISO 1600

Up to ISO 400 there's essentially no difference in noise the three cameras although the EOS 350D (Digital Rebel XT) does exhibit better per-pixel-sharpness. At ISO 800 the EOS 350D hangs on to this sharpness where as the E-500 and E-300 images have become softer, with the E-500 looking cleaner than the E-300 especially on the black patch (shadows).

At ISO 1600 there's a marked difference between all three cameras; the E-300 is obviously noisiest with both luminance and chroma noise, the E-500 comes next with a cleaner image but obvious softness (noise reduction), it exhibits less detail than the E-300 at this sensitivity, lastly the EOS 350D which looks less sharp than it did but still maintains some detail. In comparison the EOS 350D ISO 1600 (2000 equiv.) image looks about the same as the E-500 / E-300 do at ISO 800.

Luminance noise graph

The E-500's new noise reduction filter delivers lower luminance noise than the E-300, especially at ISO 1600. Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis. Gray refers to the middle gray patch, Black refers to the black patch.

Chroma noise graph

Here we can see that the E-500's noise reduction filter affects chroma noise the most and starts at ISO 800. Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of chroma (from the gray patch) on the vertical axis.

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