When we’re out shooting a project, it’s absolutely critical for us to know the various strengths and weaknesses of our photography equipment. A lot of that revolves around the overall quality of the image we can create in a given shooting environment. Is it dark? Bright? High contrast? Lots of fine detail or color? Answers to these questions found in our Canon 5d native ISO test will determine how we approach the task of getting the best shot.
Part of the image quality equation involves the sensor’s sensitivity to light – measured in ISO (or ASA, or decibels). We can change the sensor’s sensitivity to be less if the scene is too bright, or more if the scene is too dark. In each case the number of photons required to achieve a neutral exposure changes proportionally. An ISO of 100 requires twice as much light to create the same exposure as does ISO 200, all other settings being equal.
What’s important for our purposes is that each camera has what we’ll call “native” ISO’s – a level of sensitivity that is ideal and generates the least amount of image noise. ISO’s that fall outside of the native ISO values are achieved by a somewhat nefarious method: the camera amplifies the sensitivity artificially. The short story is that artificial ISO’s will have degraded image quality – more noise, less contrast, less detail.
One might think that the true native ISO of the camera is the lowest setting – in the case of most DSLR’s, that would be ISO 100. Surprisingly, ISO 100 is not a native ISO setting for the Canon 5D Mark II. Neither is ISO 125. As it turns out, the lowest native ISO setting for the 5D Mark II is 160.
The conventional wisdom is that as ISO increases, image quality decreases due to noise. But we see that that it not all all the case. ISO 320 has less noise than ISO 250, 125, and probably less than 100 as well. Now, you might think that since 320 is a multiple of 160, the “native” ISO’s would all be multiples of 160. But there is really no such pattern. ISO 400 also appears to have very minimal noise, and ISO 1250 is clearly a winner as well.
Of course, we see that at ISO’s above 1600 the noise profession is in fact linear. This suggests that all ISO’s in that range are amplified artificially and there are no “native” settings to be found.
So why is this test important? As we discussed in the RAW vs. JPEG series, image quality is paramount in projects that require extensive color grading and/or post-production exposure adjustment. Knowing that ISO 1250 produces far less noise than ISO 125 allows us to make smart camera setting adjustments during a shoot to maximize our post-production latitude.