Can anyone explain this

Can anyone explain this

Ok, I’ve been pondering this and I remain baffled. This image is about 10% of full frame - of an image I’ll be posting soon. It’s cropped from an image of rushing water, a little white water that of course creates random splashes and drop of water.

Why, why is the stream of water broken up in equal little segments? I’m assuming this is a water droplet flying through the air. Why doesn’t the camera record the streak? The shutter speed is .3 sec. I don’t think any other tech info is relevant? but I could be wrong.

Why does the smooth water (non-specular highlights) record smooth and contiguous as one would expect with longer shutter speeds, but the water droplet doesn’t? Ok, with the smooth water, it’s simply a continuous feed of water molecues recorded during that .3 sec giving the “illusion” that the water is flowing smoothly - but in reality it’s thousands of molecules added together… ok, I think I get the smooth water part.

Still am unable to understand why the flying drop is recorded in this way? I can think of a jet flying across the night sky and it records the blinking red lights and they come out in a similar display. However the planes red lights are blinking… so that makes sense.

The water drop travels a certain distance in the .3 seconds. Why is it not recorded as a smooth line?

I’m no physicist… and I’m hoping someone can help me understand.

Just thinking about this… it has to be mechanical on the camera side of things. Perhaps it’s the duty cycle of the sensor? Kinda like refresh rates for video?

Anyone have a clue?

Well Lon, you have me stumped on this one. I find it odd that you have at least four separate arcs of different sizes, all consistently about perpendicular to the current. And you also have a series of six larger dots running diagonally at consistent intervals. I initially considered sensor debris, BUT that doesn’t explain the odd repeating patterns (on the arcs they are the same shape. All very curious… maybe someone else can answer this riddle.

Learning the camera model used could be of some help.
I would inspect the sensor for dirt and/or a scratch and look for the condition on adjacent images. Fortunately, it looks like something that can be cloned out. GL

The droplets are rising and hence moving slower than the cascading water and you are looking at a series of droplets? Heck if I know, but that is my WAG.

I have no answer Lon, but this reminds me of the way plane trails appear as a series of red dots in my nighttime Milky Way images. I searched for what causes that, and found nothing on point. However I believe it is because the running lights on planes flash intermittently. Not sure how that relates here, but it looks similar. And it is amazing that you got this many dots in only 0.3 seconds.

Yeah, sorry, some extra info might be helpful. Camera is Nikon D800E, Lens Nikon 28-300mm.

Which leads me to something… What does the D800E NOT have, that the D800 does? The anti-aliasing filter! I’m reading up on that wondering if that may be it.

It’s not dust or scratches, those show up as dark as you know. There were a few dust spots within this frame that were cloned out. Looking at other frames, it’s definitely water drops splashing through the air. I notice too that they are pretty much perpendicular to the flow.

Interesting mystery

One thing I’m seeing is that the length of the drops and their separation aren’t the same. In fact, they vary quite a lot. That makes me suspect that there’s a physical phenomenon at work outside the sensor. Question: Were you using a polarizer?

@Dennis_Plank, I’m fairly certain I was using a polarizer. In fact I had it on most all this last weekend when these pics were taken.

Here are 3 more. The first two from the same scene, different frames and different parts of the frame. The second one is the most bizarre to me because it doesn’t seem to h ave a source like the others where a splash seems to be the starting point. I’ve been going through my images and found the 3rd example from the fall of 2018. No idea if I had a polarizer on at the time, it’s possible.

from 2018:

Maybe the drops are like the satellites that are spinning around reflecting light making them appear like blinking lights.

Nailed it! The droplets is rotating.

Hmmmm, this initially sounds like a good explanation. But in thinking about this further, I’m not so sure. A water droplet is basically a clear ball right? Imagine a clear, glass marble. It wouldn’t matter how it’s rotated it would reflect, refract and transmit light the same, no matter the rotation.

Now that I think on it, all the night-sky images of satellites I can think of are straight line images - like a falling star, meteor, etc. A spinning satellite essentially has the same reflective surface no matter how it’s rotated. It’s not like it’s silver metal on one side, and black on the other.

Anyway, here’s the full image the shows an even larger example of the phenomena. It’s the full frame view of the first post above. Notice the serrated streaks between the submerged rock and the white water caps. The arched droplets in the original post can be seen below and to the left of the larger streaking drops.

Just plain weird. I’m not losing sleep over it, but it remains a mystery to me

Here’s a guess.

The line doesn’t represent the movement of a single drop. Rather each dash is a single drop. A set of drops flew across in the same trajectory. When photographed with a slow ss they appear as dashes. Had this been shot at a slower ss you would have had a continuous line instead of a dashed line.

1 Like

Lon, this takes me back to the part of my PhD thesis on light scattering from small particles. Each “streak” is a single drop of water flying in a standard arc determined by the speed of the drop, the initial angle of flight and gravity (think baseballs, footballs, missiles, etc). I expect that the what you’re seeing is determined by the scattering angle (angle between the sun, the drop and the camera. When light is scattered by a single particle, the amount of light scattered changes with the scattering angle, sometimes slowly and sometimes quickly. The magnitude of that change can easily be 1000X so the bright areas are where there’s lots of scattering and the dark areas are where there’s only a little scattering. The rate at which the scattering changes with angle depends on the size of the drop, so you should see different lengths of bright/dark for different size drops as well as for different scattering angles. (The scientific description is called Mie Scattering, if you want to investigate further.)


I have to guess it has all to do with the droplet itself. If you get past an assumption that it’s round and stable, it’s easy to start think of high speed changes in how it reflects light. After all, we’re only seeing .3 seconds and a “launched” droplet could take more time than that to settle into a round form.

Thanks, Mark. I was hoping you’d chime in.

Rotating is a better word than spinning.

Thanks @Mark_Seaver! I knew someone on here would chime in to provide me an education! Your explanation sure seems to be at the heart of the observed phenomenon. Let me see if I can muddle through the sequence of events.

  1. The water in rushing rivers is dynamic, always in flux, rising, falling, currents, eddies, rocks, boulders, debris and the river bottom creating waves, splashing, white water, etc.

  2. Streams of water are “launched” routinely when opposing currents or direction of flow hit each other, collide with rock, etc.

  3. These little streams of water come out much like water comes out of a “Rainbird” sprinkler. It’s a “stream”, but the stream separates in to individual droplets (either naturally or mechanical - think of the mechanical sprinkler.) And so @Hank_Pennington, your point fits in here in that you are correct, droplets are dynamic, change shape through the launch and flight process; may or may not ever become round - like my glass marble analogy… :roll_eyes:

  4. How and where these streams of water are launched determine the launch angle, the force and the volume, which create differing archs, speed, distance and trajectories. And so your observation @Dennis_Plank, confirms the variation in drop sizes, volume and all those variables to cause slight variations in size and length (and ultimately the light scatter properties…)

  5. And so finally we have the photographic capture. @Igor_Doncov you would be correct in the .3 second exposure of course allowed the light to be recorded long enough to create a blur - captured on the sensor. Of course longer shutter speeds would create the effect of a longer, unbroken stream - faster shutter speeds of course freezing the motion and more likely seeing droplets, rather than dashes.

  6. And so we come full circle to @Mark_Seaver 's explanation. So why don’t we see these little dashes everywhere the water is splashing? Well, I’m guessing because all the stars don’t line up. In other words, the light being scattered at varying angles through the drops has to be just right, relative to the position of the camera. There might not be direct light falling in other places, and yet other places where the angles (as well as speed, volume, arch and trajectories…) don’t line up for this little phenomenon to be captured by the camera. Guessing.

Lastly, not to discount the spinning or rotating variable. I’m sure it’s possible even likely that the droplets could be rotating in flight - As such, the scattering properties could change as well depending on speed or rotation, geometry of the droplet, etc.

So, Whew. Everyone gets a gold star for my lesson in physics and optics today. Mystery solved!

Thanks everyone for pitching in. I found this enlightening and educational.

1 Like

Lon, I was trying not to write a tome, but there is more. It is well known and well documented that raindrops that are larger than about 0.1 mm in diameter oscillate between prolate spheroids (think frisbee shape) and oblate spheroids (football shape). That will change the size of the circumference that’s in the same plane as the sun, drop and camera. So you can have that in addition to the variation in scattering vs angle. At smaller diameters, the surface tension of the water insures that the become round very soon after they are launched.

In one of your close ups, my guess is that you don’t see the complete trail because part of the flight path is in the shade. I’m very sure that each arching trail is a single drop. I suspect that the key to seeing the broken arc trails is getting occasional single drops launched. If there are lots of drops launched then you get full streaks.

Yes, physicks if phun and sometimes it affects our photos.

1 Like

I’m by no means an expert, but would venture to guess that they might have been individual droplets, streaking from the .3 shutter speed. I would imagine if the shutter speed was increased it would eventually freeze them into dots. A cool experiment, and an interesting thread!

Okay this has been a fascinating discussion and we need to have a geologic point of view. Water in rivers is always moving down and it is affected by multiple variables such as gradient surface texture, trees/plants, shoreline, etc. Water flows in rivers are either laminar or turbulent. Sometimes you can have both and they are affected by little microenvironment’s. In the case of the smooth flowing water in a rapid, it is probably laminar flow and then becomes turbulent flow when it encounters impeding factors such as increased gradient, rocks, etc. something impeded this particular drop at this point in time and allowed it to bounce off the laminar flow. The physics has been well explained by Mark. I have included another image taken in Costa Rica which shows the same effect. Here you can see the transition between laminar flow and turbulent flow.