ISO & MacroAlthough Canon has publicized the high-quality high ISO of the Canon S90, much has been left to desire. It is true that the high ISOs of 1600 and 3200 work relatively well (as tested while crawling through the Cu Chi Tunnels of Vietnam) to other compacts or even older DSLRs, but it would be much nicer to have ISO 80 through 400 free of splotchy chromance noise. Sometimes the race to have the highest or best is overkill, and simplicity is king. Canon did take the bait and engineered the S90 into the ISO wars rather than focusing on extremely clean low ISOs. The macro function works well, but focus is sometimes a problem and the sharpness does fall-off at the edges. However, simply recomposing and taking another photograph overcomes focus issues. Despite any drawbacks, the macro function is fabulous! Also, the Canon S90 has a nice autofocus magnification window option. When activated, this option superimposes a large box in the center of the LCD with the center of the scene magnified. This helps in landscapes and macro compositions to determine if the scene is really in focus, and it especially helps in taking sharp macro shots.
From Canon S90 Review