29/06/2015
Author: Matt Jaskulski, University of Murcia
We presented the results of our most recent study about the influence of the longitudinal chromatic aberration on the depth of field during the ARVO 2015 conference in Denver, CO.
Concepts
If the eye is focused at a given distance, then objects located either nearer or further away will produce blurred images on the retina. Although theoretically a perfectly clear and in-focus retinal image is formed only when the object is precisely optically conjugate with the retina, a slightly defocused image will also be interpreted in this way by the brain as long as it is positioned within the optical extent of the depth-of-focus (DOF). Related to the DOF is the depth-of-field (DOFi). It can be defined as the „projection of the dioptric interval of the depth-of-focus into free space”. The observer is unable to detect blurring of objects within this interval and perceives them with maximum visual acuity.
The longitudinal chromatic aberration (LCA) is the dependence of the refractive power of the eye with wavelength and is one of the important cues for the accommodative system that affects its response and accuracy.
Measurements
We measured aberrations of 7 young subjects while showing them a target at 3 different distances to make their eyes accommodate. We used a custom-made adaptive optics system equipped with a 1024-lenslet Hartmann-Shack sensor, a deformable mirror (Mirao 52e, Imagine Eyes), and a Badal system controlled by the subject. The target was presented on on an OLED microdisplay that was covered with color filters.
Results
The figure above shows that there is no difference between the eye's response to B&W and green stimuli. The DOFi extend in these cases right up to the „ideal response” line. This confirms the statement that the eye accommodates only the minimum amount, enough to place the target within its depth of field and see it relatively clearly. The fact that the LAG and DOFi for polychromatic stimuli don't differ from those for monochromatic green indicates that they are not influenced by the presence of the LCA.