Dynamic range
Our laboratory tests indicate that the D90 has a dynamic range of around 10EV, while the EOS 550D’s range is closer to 12EV. This may be a little surprising given the smaller size of the Canon camera’s photodiodes, but in practice the 2EV difference isn’t apparent and generally the D90’s JPEG images benefit from a slight boost to the contrast.
Both cameras allow the dynamic range of images to be optimised. With the D90, Active D-Lighting can be applied at one of four levels (plus Auto and Off) to darken highlights and brighten shadows. Like the EOS 550D’s shadow brightening Auto Lighting Optimiser (ALO), its effect can be difficult to predict, but its highest setting can be useful with high-contrast scenes, although it may be accompanied by an increase in the level of noise visible in the brightened areas.
The EOS 550D also has a mode called Highlight Tone Priority that is used to preserve and darken the highlights, but this cannot be used in conjunction with ALO and it can therefore be more beneficial to use the exposure compensation facility to protect the highlights and let the camera concentrate on adjusting the shadows.
