Physical Limits in Digital Photography

Digital photography has made immense progress over the past 15 years, particularly in increasing resolution and improving low-light performance. But continuing progress in these aspects of performance is not possible, because cameras are now approaching the limits imposed by the basic nature of light. This article looks at the physics that explains these limits. It shows how the fact that light has the characteristics of both particles and waves puts caps on resolution and “film speed” that are not far beyond the performance of current high-end dSLRs, and are already impacting pointand shoot cameras. Resolution is limited by the wave phenomenon of diffraction: the current generation of fullframe sensors begin to be diffraction-limited at about f/10 and above, and the best APS sensors at about f/7. More pixels can only improve resolution and contrast at wider apertures and if new lenses are up to the task. Pocket cameras begin to be diffraction limited at f/2.4 and above, which is faster than all but one available lens. High ISO performance is limited by the number of photons available per pixel. ISOs above about 3200 will always result in noise, no matter how much sensors are improved. Actually, the dynamic range of current dSLRs implies that noise in the deepest shadows is limited by photon count even at low ISOs. These limits change the nature of tradeoffs that photographers have been making concerning film or sensor size, depth of field, and sensitivity.