On the negative side 10

B&W negative time exposure of train crossing at night
So for our next negative from the mists of time, we have this authentic B&W image from Florida, back when I was experimenting with random films and developing them in the bathroom. It’s grainy partially from being old film, partially from being a time exposure in the dark, and partially from developing at a less-than-ideal temperature; film does best when the chemicals are 20°C, but even the cold water came out of the tap in Florida during the summer at better than 25° – subsequent efforts involved moderating the temperature of the chemicals with an ice bath. Anyway, what we’re seeing here is a train bridge at night, a long exposure as the train passed through, thus the streaks of light atop the bridge. [As a side note, I always find it disconcerting that train bridges have no guardrails, but then they don’t really need them, and if the train starts to leave the tracks, ain’t no railing gonna do a damn thing about it. Yet I still expect to see them.] This image has an anomaly, however, and it takes a little to grasp it.

The anomaly comes from the glow in the water, seen in the lower half of the frame. The lights of the train were reflecting in the water as they passed, and this is normal and expected. What’s not normal are the dark periodic arcs in those reflections, because they don’t make immediate sense. The exposure was for an unknown time, but at least thirty seconds, possibly much longer – doesn’t matter too much, because the key bit comes from the passage of the train lights, so call it ten seconds or so. It’d be easy to consider these shadows, but the moving lights wouldn’t throw a distinct shadow in one location – instead, they’d produce tracking shadows that would pan across the frame during the exposure and thus almost eradicate themselves in the reflections thrown from the same locations when they weren’t there. Not to mention that there wasn’t anything (like guardrails) to throw shadows in the first place.

So here’s what I think is going on, and engineer Jim Kramer agreed, years back when I first showed him the photo: it’s an artifact of ripple interference. Bear with me here.

Any water source will show ripples a great percentage of the time, mostly due to wind or breezes, sometimes due to flow, and these will generally be in one direction. And then, disturbances (splashing, vibrations) may throw out another set, usually expanding in concentric circles from the source; these won’t eradicate the existing linear ripples, but intersect with them, in places causing combined-height wave peaks, in others cancelling each other out and producing very localized smoothness. So as the train passed over the bridge, it produced vibrations that carried down the bridge supports and into the water, and these ripples interacted with the existing ones to create a double, overlapping pattern. And at key points in this pattern, the water simply faced the wrong way to send reflections of the train lights back to the camera. Because one set of ripples originated from fixed points, the bridge supports, the pattern presented a more-or-less immovable interference pattern.

The part that doesn’t seem to support this hypothesis is the number of bridge supports versus the number of interference arcs, plus the fact that they don’t appear to line up. And I can’t explain why there’s only one arc on the right side but dual arcs for the rest. So without experiments or video that seems to show how these patterns work, I’m not 100% convinced that this is right. Yet I also don’t have any other explanations.

Notice how, over on the right side of the frame, the reflection from the bright light in the distance cuts right through the dark arc, but this is expected because that light was shining on the water well before and after the train had passed, so the interference pattern would not have existed at those times. I don’t recall for certain which way the train was traveling, but I was favoring right to left, and the reflections kind of support this too, in that they’re extending further out/down from the bridge on the right side, where the ripples could travel farther while still catching the train’s lights.

Anyway, I thought it was an interesting artifact, and I remember noticing and pondering about it after scanning in the negative, way back when. And since there’s little to shoot and no time to shoot it anyway, this is what I got right now ;-)