Bioinspiration Example I - Low light lens inspired by the eyes

In most vertebrate, the iris is generally assumed to be immobile and its pupil does not change in size and response to variation of ambient changes. The plecostomus catfish were chosen to study because they may show extensive pupil mobility without providing the extent and speed of migration [1]. An explanation of this pupil can be elaborated further that they may have the tendency to reduce the effect of any longitudinal spherical aberration [2]. However the plecostomus catfish has crescent-shaped pupils that functions primarily to reduce such aberration. Addition to that, few studies were investigated that the density of retinal ganglion cells with crescent-shaped isodensity contours in retinal whole mounts of a weaver. 

Figure A: Condition of pupil size with absence      Figure B: Condition of pupil size after

of visible light.                                                            60 minutes of white light exposure.

Based on the Figure A, it was the initial size of the pupil with the absence of visible light. As for Figure B, the plecostomus fish was exposed with white light after exposing on it for 60 minutes which resulted decrease in pupil diameter and outgrowth of iris. Results showed that the response of the pupil towards light is slow, about half of the contraction happens from1-8 minutes and full contraction usually takes around 35-45 minutes. In general, higher light intensity speed up the pupil contraction much faster compared to the results obtained [1].

The low light sensitivity of the lens is a very important specification. Biomimicry from cat fish eyes of its capability to see in low light has inspired to increase the capacity of lens that can captured and shoot images at night and at low light environment.The iris of can control the amount of light that hits the lens sensor.  When there is a lot of light the iris opening is very small, and when there is very little light, the iris opens up as much as it can. This mechanism is similar to how cat fish controls lights entering its iris whereas its eyes changing from a normal iris shape to an omega iris shape.  In most lens setting is automatic, but some can manually fine adjustments.  When iris lens open, it can get the most light on the sensor hence capable of objects are still in focus by the lens. Application from low sensitivity lens can be found in camera lens, monocular, riflescopes and many more [1].  Through this lens we can see on objects due to maximum contrast with a background beyond human eye sensitivity.

Figure 1: Night vision rifle scope lens that capable of focusing object at low light environment. 

Reference :

[1] R. Douglas, S. Collin and J. Corrigan, "The eyes of suckermouth armoured catfish (Loricariidae, subfamily Hypostomus): pupil response, lenticular longitudinal spherical aberration and retinal topography", Journal of Experimental Biology, vol. 205, no. 22, pp. 3425-3433, 2002.

 [2] C. Murphy and H. Howland, "The functional significance of crescent-shaped pupils and multiple pupillary apertures", J. Exp. Zool., vol. 256, no. 5, pp. 22-28, 1990.