The ability of a camera to take low noise images under low light conditions is extremely valuable. Given that almost all digital camera these days have more than enough megapixels, low light performance is arguably one of the most important factors to consider when purchasing a new camera.
The purpose of this thread is to discuss methods for testing and comparing the low light performance of different cameras. What testing method(s) would enable a prospective buyer to judge which camera performs better under low light conditions, and how much better? What exactly should be compared, and how would you go about doing it?
This is not as simple as it may appear. Many respected camera review sites test and compare low light / high ISO performance of cameras, but it is not at all clear (at least to me) what their tests are trying to achieve, or even if their comparisons have any real meaning at all.
I will start the discussion by giving some of my own ideas on this topic. On 15/2/09 I started a thread entitled ‘Large Sensors and Image Noise’, specifically to provide some background information for this topic, and much of what I write here is explained in greater detail in my first posting to that thread.
Consider the common situation where a prospective buyer would like to know how camera A compares with camera B, in terms of low light performance. An obvious example would be choosing between a top end point and shoot (say a Canon G10), and a basic SLR, for example a Canon EOS1000D. To my mind, two key questions that should be included in such a comparison are :-
How much intrinsic low-noise advantage (if any) is provided by the larger SLR sensor? The comparison should show two images, one from each camera, which directly illustrate the lower image noise provided by the larger sensor. The key concept here is that both sensors must receive the same number of photons, and a method of doing this is given in the thread ‘Large sensors and Image Noise’. This is an important measurement because it cannot be predicted from the specifications.
How much better will the SLR be when the conditions are really tough, and both cameras are flat out capturing all the light they can get? In other words, what advantage is gained by the better camera as a whole, including the lens system? Express this advantage in terms of stops, and show two images, one from each camera, that illustrate this advantage. Again, see the previous thread for details of taking this measurement.
I contend that these are key questions that the prospective buyer would like answered, and the (admittedly few) online tests and comparisons that I have seen do not seem to answer either question!
Any agreement or disagreement that these are important key questions?
Any suggested alternative testing/comparison methods?
Any comments on what the low light (high ISO) tests in dpreview.com, for example, actually mean?