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ISO Accuracy

The actual sensitivity of each indicated ISO is measured 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 a calibrated Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV (the margin of error given in the ISO specifications). Measured ISO from the EOS 550D is within +/- 1/6 EV of indicated ISO, and the 550D gives almost exactly the same luminance readings from middle grey across its entire ISO range, which represents excellent consistency.

ISO Sensitivity / Noise levels

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. This 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 (i.e. ISO 200, 1/200 sec for consistency of exposure between cameras). The image sequence is run through our own proprietary noise measurement tool (version 1.6 in this review). Click here for more information. Room temperature is approximately 22°C (~72°F), simulated daylight lighting.

Canon EOS 550D vs. Nikon D5000, Pentax K-x and Canon EOS 500D

  • Canon EOS 550D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Standard PS), High ISO NR Default (off), JPEG Large / Fine
     
  • Nikon D5000: Nikkor 50 mm F1.4 G lens, Manual Exposure, Manual WB,
    Default Parameters (Standard), High ISO NR Default (on, 'low'), JPEG Large / Fine

  • Pentax K-x: Pentax 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Standard PS), High ISO NR Default (off), JPEG Large / Fine
     
  • Canon EOS 500D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Standard PS), High ISO NR Default (off), JPEG Large / Fine
       
  Canon 550D Nikon D5000 Pentax K-x Canon EOS 500D
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200
ISO 6400
ISO 12800  

Given the density with which its sensor is packed with photodiodes, the EOS 550D delivers an impressive balance between detail capture and noise reduction at its default noise reduction setting. Although fine detail is clearly blurred at ISO 6400 and 12800 compared to the lower settings, the areas of highest contrast still contain some recognizable detail. The real star of this comparison is the Pentax K-x though, which at its default NR setting delivers an impressive amount of detail right up to ISO 12800. Despite its lower pixel count, images from the Canon EOS 500D are slightly noisier when compared directly against the 550D, but we certainly can't say that the newer model offers any significant improvement - except of course for the larger files.

Noise graphs

The graphs below show us that the Canon EOS 550D compares very favorably to its competitors in terms of chroma noise, consistently showing slightly lower levels. Only the 500D diverges significantly from the others in the group, and recorded chroma noise levels are higher (but only slightly in 'real-world' terms) than the other camera from ISO 1600 upwards. In terms of black and grey noise levels, the EOS 550D gives a good showing too. Only the Nikon D5000 offers lower noise levels on these graphs, and then only beyond ISO 1600, where noise reduction really kicks in. For all three types of noise, the Canon EOS 500D gives the highest readings at the higher end of the ISO scale.

  Canon EOS 550D
Chroma
Black
Gray
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.

High ISO noise reduction

By default, (and somewhat confusingly) the Canon EOS 550D applies high ISO noise reduction at all ISO settings, but it can be disabled via custom function II 5. Here, we can see the effects of high ISO noise reduction where it really counts - at the higher ISO settings, in both raw and JPEG files.

You can see that when high ISO noise reduction is disabled, JPEG images display more chroma (color) noise than those taken when NR is turned on. With noise reduction turned to 'strong', it is clear that images are being fairly aggressively processed, although the downsides of this processing only become a significant problem beyond ISO 3200, where fine detail starts to be smoothed over. At the highest ISO setting of 12800, chroma noise hits an unacceptable (or at least unattractive) level with noise reduction disabled, and the optimal setting when shooting JPEG is 'standard', which hits a pretty good balance between noise reduction and detail preservation.

The raw files shown here are processed through Adobe Camera Raw with noise reduction dialed down to zero. This allows us to see the images in as close to their unprocessed state as possible, and it is obvious that at all NR settings, even 'off', the EOS 550D is applying some noise reduction to JPEG data before it is written to the card.

  ACR (no noise reduction) JPEG (NR 'off') JPEG (NR 'STD') JPEG (NR 'Strong')
ISO 1600
ISO 3200
ISO 6400
ISO 12800

This graph shows noise as standard deviation of luminosity at all of the EOS 550's high ISO noise reduction settings, from ISO 1600 and above. In all cases it is interesting to note that the results with noise reduction turned off, and those when it is turned to 'low' are very close. There is a sudden drop in measured noise when noise reduction is switched to 'Standard' (the default setting) and another, fairly large decrease when it is dialed all the way up to 'strong'. In fact, you can see from comparing the values on the y axis that at all of the ISO settings we've shown here, measured noise almost halves when NR is switched to 'strong' compared to measurements taken when it is switched off.

RAW noise

Here, we have converted raw files from the Nikon Canon EOS 550D, Nikon D500, Pentax K-x and Canon EOS 500D in exactly the same way, in Adobe Camera RAW, with sharpening at default settings, and noise reduction turned off (to 0). Naturally, these images look somewhat different when processed using the bundled raw converters, but by processing the files in the same program in the same way, we achieve the closest thing to a 'level playing field' that is practical (whilst still being meaningful).

With ACR's noise reduction turned off, we get a better idea of what the sensors in these cameras are actually capable of. At ISO settings up to ISO 800, there is very little noticeable difference in noise levels and detail capture between these four cameras. There are differences, naturally (you can see the data in the graphs below this table) but they don't translate into markedly different looking images. At ISO 1600 and above, however, the performance gaps become clear, with the EOS 500 giving the noisiest results with the least detail, and the Pentax K-x delivering the best output in our opinion, with plenty of detail still showing through the (inevitable) noise even at ISO 12800.

The EOS 550D is a middle ground. Images are less noisy than those from the slightly lower resolution 500D, but detail isn't quite as well defined as it is in images from the K-x. Naturally, sensible post-capture noise-reduction in ACR or any other raw conversion software can make all of these images a good deal more attractive than they appear here.

  Canon 550D Nikon D5000 Pentax K-x Canon EOS 500D
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200
ISO 6400
ISO 12800  

Raw Noise graphs

Using a common raw converter tells us a lot more about the actual characteristics of these cameras' sensors when it comes to noise. As usual, measured noise levels from all of these cameras are higher in raw mode (without any noise processing) compared to JPEG. Again, the EOD 500D gives the highest levels of measured noise, but the 550D is very close behind, and even gives (fractionally) higher figures in grey and black noise towards the lower end of the ISO scale. Once more the Pentax K-x gives the lowest measured results where it counts, towards the top of the ISO scale, but the differences you can see here don't translate into huge discrepancies in image quality, as you can judge from the images above.

  Canon EOS 550D
Chroma
Black
Gray
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis. NOTE: The scale of this graph is different to the JPEG noise graph towards the top of this page, and goes up to a standard deviation of 20, not 10, to account for the higher levels of measured noise in raw capture mode.
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Comments

Total comments: 2
BobFoster

Seriously Pentax has around 2% of market share :O The K-X and K-7 are really good cameras for there categories and price etc... Given that they have only 2% market share should I be scared to buy a camera from them? Could they just say one day right we will no longer make cameras and that's it? To add to that question what other lens do mount on Pentax?

1 upvote
reanim888

The camera was ok, but as soon as I dial in my personal settings, problem is still there!! aarrrgg!

I just sent them the camera back to Canon, waiting for explanations.

1 upvote
Total comments: 2