How we see see the world is made possible by specialised rod and cone photoreceptor cells in our eyes. Rod cells are more sensitive to light, and grant us our low-light night vision. However they aren’t able to distinguish between colours, whereas cone cells are. Human beings usually have three types of cone cells, each able to perceive different wavelengths of light (approximately between 400-700nm), roughly translating to red, green and blue light. This means our vision is “trichromatic”.
Many species of animal, including a number of birds, have 4 types of cone cells, granting them tetrachromatic vision. This extra 4th type of cell is able to perceive into the near ultraviolet spectrum of light (300-400nm), which is invisible to the human eye.
We are taking images of preserved bird specimen skins, both in human visible spectrum (what we can see) and in the ultraviolet spectrum (300-400nm). This is achievable using a modified DSLR camera which has had its UV filters replaced with quartz, allowing for full light spectrum transmission to the sensor. We also use a specialist UV lens (Nikon UV 105mm F4.5 Lens) which contains quartz elements. We are currently using a pair of filters on the front of the lens to block out either everything except what we can see( 300-400nm) or everything except near UV (300-400nm).
By analysing the four separate “colour channels” (Ultraviolet, Blue, Green and Red) in the images, we will be able to determine, among other things, which species utilise UV reflecting plumage.