Figure 1.

Trigonometric calculation used for obtaining a theoretical value of the visual acuity. Visual acuity was calculated in cycles per degree (cpd) using the following formula: 1/(2(arctan(s/f)). f: focal length; s: distance between the center of two red-green double cones; ΔΦ: inter-receptor angle at the nodal point of the lens.

Haug et al. Frontiers in Zoology 2010 7:8   doi:10.1186/1742-9994-7-8
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