“The Principal Eyes of a Jumping Spider Have a Telephoto Component”, 1980-12-11 ():
Jumping spiders are a cosmopolitan family (Salticidae) of predators that can make visual discrimination between prey and mates1,2. This task is mediated through the anterior median eyes, described by Land3 as consisting of a corneal lens and a motile retina that comprises 4 layers of receptors embedded in a matrix. The retinal matrix contains a pit distal to the receptors and symmetrically centred on-axis.
We have now found that in Portia fimbriata (Doleschall) and some other species, this pit has a refracting interface that increases the focal length of the eye beyond its axial length, thereby magnifying the retinal image and increasing visual resolving power above that possible with only a corneal lens. The most effective part of the conical pit is its rounded apex, which augments the corneal lens to provide a telephoto system that increases the overall focal length by about 1.5×.
This mechanism is of particular value to small spiders like P. fimbriata, for the possible axial length of their eyes is constrained by the small size of their prosomae (Figure 1).