I hope that sometime soon I can sleep at normal hours again, but as it goes I keep waking up. This time I was staring into the dark kitchen (which is by my bed in the ‘studio’ flat kinda way I live) and .. looking for our “friends”. Right now I have a little bit of a cockroach problem, and have just put out some traps. I was curious how many of these things were walking around in the dark, since they don’t all come out in the day. There were a few as I expected.

What I found very interesting though, was that I could see little dark patches and spots on the floor where perhaps a little bit of food that needs to be cleaned was laying, or even a cockroach was walking.. but a very surreal aspect of this was, anything under a certain size was completely invisible if I stared at it, but if I allowed my eyes to wander I could see it in the periphery. Assuming that usually you can see in front of you and vision is less sensitive to the edges, this was very odd indeed.

So perhaps you’re thinking that I’m just seeing things and that actually the dots are my imagination since there’s not even enough light.. so after staring for 15-20 minutes mesmerized by the curious things I was seeing, I took my small camera and took a bunch of photos with a flash in the dark. Without moving the camera (similar to looking into a star field) I had a couple of sequential images to compare and sure enough, the dark spots were bugs, and the bits that weren’t moving were either bits of food or cockroaches dead from previous accidents. It all sounds pretty horrific, but in total I think there’s maybe 8 walking around and laying there.. it’s not as if the floor is crawling, and hopefully the poison gets to work very quickly.

So what’s going on here? A first thought would be that when your iris is open to allow the maximum amount of light in, as with close-up photography, specifically using a macro lens on a small object, the depth of field decreases, but this shouldn’t really play a part in it since I can still see the dark lines of the tiles.

One difference between an eye and a camera is that while the film plane is flat in a camera, your retina is the inside of a sphere, which not being an optician or expert here but perhaps might affect our depth of field slightly? I would imagine that mostly what that would do would be to have a far narrower focus, since anything not directly centered would not be hitting the fovea, and inside the curve would become closer to the lens and so blurred if the lens was acting to focus the image to the center. I imagine we would be overwhelmed if everything was constantly in focus, and so it makes perfect sense that we would benefit from a small very clear area, and a large blurry area that is primarily to detect movement in the periphery.

The subject matter was 1-1.5M away doesn’t make me think I would be getting any drastic depth of field. Now I can’t imagine that the blind spot is directly centered, and I’m hoping that this is normal and not something I should get checked out.

A couple of thought sprung to mind, and were equally swiftly dismissed. Perhaps the eye is actually accustomed to more light at the center since that’s where we lay focus during the day on a cellular level, and so it is calibrated differently from the periphery? Well I suppose that might make sense, but how then would it end up less sensitive in the dark?

I also wondered that maybe the lens would be a different shape, argument for either flatter or fatter still didn’t conclude, but since in the low light there is no easy way to find focus on an object, perhaps the lens is relaxed (and so fatter?) which means it bends light differently. Could that explain why more light from off center was actually being focussed on the area of the retina surrounding the usual focus point? And that if i stared directly at a dark spot I would actually find myself staring into nothing, until perhaps the ‘dark spot’ walked back into view/out of my direct focus?

Another thought that just occurred would be that since the non focussed area would produce a blurred image, and the lens would also be producing a blurred image off center, perhaps the blur from the lens was the result of collecting more light from a larger area but not putting it into a point, so the sharpness is reduced, but the amount of collected light would actually be increased. I am thinking along the lines of the “two blurred images” (I’m referring of course to one blurred image but the two points in the eye which are out of focus, i.e. the lens and the retina) combining in a way that actually gives more information about the light intensity than the imperfect focus of the direct center of the eye. The only way I can think to describe this visually would be similar to lens flare, multiple images from internal reflections cueing up and shifting in a way that might be describable as parallax.

Anyway, that’s just a brief write up and I think I’d be wise to look further into it before making any bold statements, but I’m quite interested to see if this is documented and what the answer is.. hopefully not that there’s something wrong with my eyes!


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