  Many augmented reality (AR) applications operate within near-field reaching
distances, and require matching the depth of a virtual object with a real
object. The accuracy of this matching was measured in three experiments, which
examined the effect of focal distance, age, and brightness, within distances of
33.3 to 50 cm, using a custom-built AR haploscope. Experiment I examined the
effect of focal demand, at the levels of collimated (infinite focal distance),
consistent with other depth cues, and at the midpoint of reaching distance.
Observers were too young to exhibit age-related reductions in accommodative
ability. The depth matches of collimated targets were increasingly
overestimated with increasing distance, consistent targets were slightly
underestimated, and midpoint targets were accurately estimated. Experiment II
replicated Experiment I, with older observers. Results were similar to
Experiment I. Experiment III replicated Experiment I with dimmer targets, using
young observers. Results were again consistent with Experiment I, except that
both consistent and midpoint targets were accurately estimated. In all cases,
collimated results were explained by a model, where the collimation biases the
eyes' vergence angle outwards by a constant amount. Focal demand and brightness
affect near-field AR depth matching, while age-related reductions in
accommodative ability have no effect.
