ISO Sensitivity / Noise levelsISO 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. Nikon D700 vs. Sony DSLR-A900 vs. Canon EOS 5D vs. Nikon D300
D700 Higher ISO settings
All cameras in this comparison perform very well up to ISO 400 when we see the first hints of chroma noise appearing on the Sony A900 output. At ISO 1600 all cameras still produce perfectly usable results but as the noise reduction really starts kicking in the D700 produces visibly more detail than the competitors. The D300 and A900's sensors are much more densely packed than the D700's and the Canon 5D is simply one generation older than the brand new Nikon. These factors show in the image output. As you go up the ISO scale you see a small, but increasing, amount of luminance noise (grain) creeping into the D700 images but thanks to Nikon's very sensible approach to noise reduction it always maintains a relatively pleasant, almost-film-grain-like, appearance up to the very highest settings. Unsurprisingly the D700's performance in this test is very similar to what we saw in the D3 review a few months ago. This means you still get perfectly usable results at ISO 6400 and while due to Nikon's light-handed approach to luminance noise reduction you get some graininess at the highest ISO settings the results still look surprisingly sharp and detailed. Only the maximum ISO setting (25600, something that was unheard of only a year ago) should pretty much be reserved for emergency use only. The ability to produce usable results at such high sensitivities makes the D700 the camera of choice for any photographer who is having to deal with challenging light conditions and prefers the D700's smaller dimensions over the D3. It's also an ideal second body for anyone already using the D3. * These results are with the cameras in their default modes, all four cameras offer some control over the amount of noise reduction used at higher ISO settings. Noise graphsNote that we normally show both gray and black results on the same graph, comparing four cameras this became too difficult to read hence we have two separate graphs, one for the gray patch (middle gray) and one for the black patch (shadows). Luminance noise graph (gray patch)The D700's noise rises in a fairly linear manner but inevitably the curve starts to get a lot steeper once you get towards very high ISO settings. The D700's measured noise is the lowest here at most settings but in reality the gap to the competition is even bigger. When you look at the actual output is becomes obvious that the other three cameras can only keep up by applying visibly more noise reduction at the higher settings.
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis. Luminance noise graph (black patch)The picture looks slightly different for the black patch (which generally represents shadow noise). The Canon EOS 5D can keep up with the Nikon up to ISO 1600 while the D300 and A900 produce more measurable noise at all settings. Again noise only starts to rise steeply once you get to the very high ISO regions when the crops at the top of this page start to look distinctly grainy.
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis. Chroma (color) noise graphThe D700's big photosites also have a significant impact on chroma noise. The D300 which has the same megapixel count but a smaller sensor can keep up but only by massively pushing up the chroma noise reduction at ISO 800 which results in visibly softer images. The D700 beats the EOS 5D at most settings although only by a whisker. The Sony DSLR-A900 with its 24 megapixel sensor has the highest measurable chroma noise and if you want to confirm that you only have to look at the crops above.
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of color on the vertical axis. |
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