The full moon is Thursday this week. They’re forecasting overcast skies and precipitation for the next several days, so I’m not sure we’ll see it at its peak, but right now, two days before full, the moon is pretty bright, enough that we don’t need to wear a headlamp to walk down to check the owl nets. Moonrise this evening was timed with dusk, and as I was looking out over the lake an hour or two after the sun had gone down, the rising moon caught my eye, hanging behind the silhouettes of the tall trees in the yard. I grabbed my camera and set it up on a tripod out on the deck. Uncertain about what exposure was necessary to capture the scene, I took several at different settings. The above was the one that most closely resembled what my eye saw. All the photos were taken at F/5.6 and ISO800, with just the shutter speed changed – this was at 1 second exposure.
Some animals can see a lot better in the dark than we can. This is largely due to the structure of the eye. The vertebrate eye contains two types of cells in the retina – rods and cones. Rods are used in capturing light, and cones are used in detecting colour. Humans have more cones than rods, which is why our colour perception is so good. We have some rods, but being primarily diurnal species we don’t need a whole lot. Other critters, on the other hand, who do a lot of moving around at night tend to have more rods than cones – colour isn’t as important at night. Cats, for instance, frequently hunt at night and are known for their excellent night vision. The average cat has about six times more rods in their retina than a human (which translates to about six times more light captured, allowing them to see about six times better). I fancy that this is what the world looks like to a cat at night. This was a 4 second exposure, so not quite six times difference, but close.
Owls are well-adapted to hunt at night, and may have among the best night vision of any land creature. Their retinas have as many as 10 times the number of rods that those of humans do, so they can see exceptionally well in the dark (this is helped by their exceptional 3-dimensional hearing, which results from their ears being off-centre from each other). Owls also have very large eyes relative to the size of their head – so large, in fact, that there’s hardly any room for eyeball muscles to move them around, and so the eyes are fixed in the skull. To look around the owl moves its whole head, and although it doesn’t have a complete 360 degree range of motion, it does come fairly close. These large eyes provide a greater expanse of retina for light collection, also contributing to their excellent night vision. This was a 15 second exposure. It might as well be daytime, you can even make out the colours of the trees across the lake.
In doing some of these long-exposure photos I often find it astounding how much light is actually available to the camera that our eye just can’t detect. It may look like the dark is rising at sunset, but it really isn’t.