Two things happen with smaller pixels. First, the base ISO sensitivity of the sensor drops because more light is needed to fill the ultrasmall pixel wells. To compensate, cameras offer higher ISO modes, which unfortunately boost noise levels in the process of increasing low-light sensitivity (see ISO 100 vs. 400 shots at left). Second, the physical characteristics of the sensor, especially the materials used to create the boundaries between pixels, are less able to prevent electronic background noise from interfering with the signals from individual pixels. Thinner, more transparent walls between small pixels also allow angled light to strike adjacent pixels, causing noise, color fringing, and softer edges-especially with wide-angle lenses set to their widest apertures.