Digital image correlation, commonly referred to as DIC, enables full-field measurements of displacements and strains from a surface of interest. While DIC offers major advantages over commonly established methods, such as strain gauges or extensometers, some questions remain in guaranteeing data precision of the DIC measurements. This paper reports on improvements in the precision of DIC measurements of large deformations in copper tensile specimens by optimized patterning and lighting conditions, as well as quantifying the improvements in the data. In the context of detection of strain localization at welds in copper canisters for spent nuclear fuel disposal, the trade-off between spatial resolution and strain resolution is critical. To quantify the improvements in measurement conditions, we propose a method for estimation of spatial resolution and noise level of a full-field strain measurement, which does not require imposing a displacement field with variations in strain or displacement of well-defined length scale.