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.

The E-410 proved to have inconsistently indicated ISO sensitivities. In reality ISO 100 proved to be slightly more sensitive than indicated (more like ISO 125) and ISO 1600 slightly less than indicated (closer to ISO 1250).

Indicated sensitivity	Olympus E-410 (actual sensitivity)	Canon EOS 400D (actual sensitivity)	Nikon D40X (actual sensitivity)
ISO 100	ISO 125	ISO 100	ISO 100
ISO 200	ISO 200	ISO 200	ISO 200
ISO 400	ISO 400	ISO 400	ISO 400
ISO 800	ISO 800	ISO 800	ISO 800
ISO 1600	ISO 1250	ISO 1600	ISO 1600
ISO 3200	n/a	n/a	ISO 3200

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), simulated daylight lighting.

Olympus E-410 vs. Canon EOS 400D (Digital Rebel XTi) vs. Nikon D40X

• Olympus E-410: Olympus 50 mm F2.0 Macro lens, Aperture Priority, Manual WB,
  Default Parameters (Normal), High ISO NR (Normal), JPEG Large / Fine
   
  
• Canon EOS 400D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
  Default Parameters (Standard PS), JPEG Large / Fine
   
• Nikon D40X: Nikkor 50 mm F1.8 lens, Aperture Priority, Manual WB,
  Default Parameters (Normal), JPEG Large / Fine
  

Olympus E-410 ISO 100 (ISO 125 equiv.)	Canon EOS 400D ISO 100	Nikon D40X ISO 100
Olympus E-410 ISO 200	Canon EOS 400D ISO 200	Nikon D40X ISO 200
Olympus E-410 ISO 400	Canon EOS 400D ISO 400	Nikon D40X ISO 400
Olympus E-410 ISO 800	Canon EOS 400D ISO 800	Nikon D40X ISO 800
Olympus E-410 ISO 1600 (ISO 1250 equiv.)	Canon EOS 400D ISO 1600	Nikon D40X ISO 1600
Olympus E-410 n/a	Canon EOS 400D n/a	Nikon D40X ISO 3200

From a noise point of view there's little difference between these three ten megapixel digital SLRs up to ISO 400. At ISO 800 and 1600 the E-410 has the cleanest looking gray and black patches although this is clearly at the expense of detail lost to noise reduction, especially at ISO 1600. The noisiest 'flat area' patches come from the Nikon D40X although it doesnt 'smear' as much detail at ISO 1600. From an overall performance point of view the Canon EOS 400D (Rebel XTi) with its CMOS sensor once more delivers the best compromise between noise and detail.

Luminance noise graph

Here you can see the clear effect of the noise reduction system (noise filter) on the E-410, it keeps measurable noise virtually flat from ISO 100 (125) to 800, rising only slightly at ISO 1600 (1250).

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.

Chroma (color) noise graph

The noise reduction system also works on chroma noise, we even see a slight dip at ISO 1600 (1250).

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of color on the vertical axis.