Strange water formation in long exposure

Started Jul 22, 2013 | Questions
rdspear Veteran Member • Posts: 4,601
Re: Strange water formation in long exposure

Looking at some of the components in the photo (leaves, specifically), this seems to be a fairly small drop.  I'd say the apex of the arc is no more than 2 feet above the surface.  So 2=1/2(32.2)t^2 - t = about .35 seconds.  I see about 16 drops from the apex to the bottom, so something would be oscillating at nearly 50Hz.  That seems quite high for a natural phenomena.

But I have no better answer

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PeterK Senior Member • Posts: 1,017
Re: Strange water formation in long exposure

Thanks AShimon!  Not sure anyone else noticed my post

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ktownbill Senior Member • Posts: 2,191
Re: Strange water formation in long exposure

PeterK wrote:

Well, here's my 2 cents:

#1: It is definitely one drop of water projected into the air at an angle, forming a classic parabolic projectile motion trajectory.

#2 Something is definitely flashing light on the droplet at even periodic intervals (the distance between the drops caught in the light display the characteristics of projectile motion, where the object travels greater distances near the ground, and smaller distances near the top of its trajectory)

#3 I doubt the full trip took the drop 2 seconds, for this simple reason:

a) from the top of its trajectory to the water's surface would take the droplet the exact same amount of time as from the water's surface to the top - they each take 1/2 the total time in flight (basic physics)

b) If the time to fall from the top of its trajectory is one second, the height would be 5 meters, or about 16 feet. Again, basic physics: all objects in free fall near the surface of the earth fall 5 meters in the first second.

c) as noted previously, it is hard to tell the exact scale, but I don't think that is a 16 ft high arc.

d) The exact time of its trajectory isn't really that relevant though.

#4 The big question is: what is causing the "strobe" effect?

- I don't think anyone has mentioned the second most obvious source of light in the frame, aside from the sun: REFLECTIONS from the WATER.

- Now, what might be causing a periodic reflection from the water?

>> The waterfall hitting some natural barrier at the base of the water that is periodically moved back and forth by the waterfall, or perhaps a pool of water in a rock that is periodically filled and emptied by the waterfall. The possibilities are endless, and I'm sure we could all imagine numerous other physical phenomena that will produce periodic motion at the base of a waterfall - in this case, periodic motion that results in the reflection of the sun's rays into the air where that drop happened to be thrown into the air.

Simple harmonic motion at the base of a waterfall seems a much more probable event than a strobe assist beam lighting that drop at such a large distance - to me, anyway.

Rather than just guessing and hypothesizing why don't you compare the frequency of the water-drops to the frequency of the AF-Assist beam and see if they match?  You aren't curious?

You need only point the flash at a photo-transistor hooked up to an oscilloscope to get your answer.

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Bill

PeterK Senior Member • Posts: 1,017
Re: Strange water formation in long exposure
1

ktownbill wrote:

Rather than just guessing and hypothesizing why don't you compare the frequency of the water-drops to the frequency of the AF-Assist beam and see if they match? You aren't curious?

You need only point the flash at a photo-transistor hooked up to an oscilloscope to get your answer.

Don't have photo transistor or an oscilloscope handy, and, if I did, I wouldn't know which flash to fire at it, on which camera, or at what settings.

There's no evidence of flash being used. If this is a hoax (which I don't think it is - I take the OP at his word), done using flash, then I'm not interested in wasting any more time on it.

The most reasonable answer, in my opinion, is the simplest: naturally occurring simple harmonic motion causing a reflection to shine on a water droplet projectile. I'm really not interested in proving it; just offering my thoughts.

I'm interested if anyone else has a more likely explanation, but I really don't think introducing a non-mentioned flash, which then fires an auto assist beam, stroboscopically, that illuminates a droplet quite far away, is a reasonable explanation. Others may disagree.

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AnthonyL Veteran Member • Posts: 3,081
Re: Strange water formation in long exposure

Lonzo wrote:

Hi,

without having read all the other replies.. this looks like a stroboscope effect - as you didn't use a flash it seems I figure that this could have been a single drop that was reflecting light in a periodical way while flying through a dark/shadowy area after bouncing off somewhere i.e. by a flickering branch/leaf somewhere in the pathway of the lightray during the exposure time - the scene seems to be able to explain that

I wonder if there was diffracted light through which the drop passed.  Diffraction has light/dark (nodes/antinodes) doesn't it?

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MOD Dale Buhanan Veteran Member • Posts: 4,280
Re: Strange water formation in long exposure
1

ktownbill wrote:

PeterK wrote:

Well, here's my 2 cents:

#1: It is definitely one drop of water projected into the air at an angle, forming a classic parabolic projectile motion trajectory.

#2 Something is definitely flashing light on the droplet at even periodic intervals (the distance between the drops caught in the light display the characteristics of projectile motion, where the object travels greater distances near the ground, and smaller distances near the top of its trajectory)

#3 I doubt the full trip took the drop 2 seconds, for this simple reason:

a) from the top of its trajectory to the water's surface would take the droplet the exact same amount of time as from the water's surface to the top - they each take 1/2 the total time in flight (basic physics)

b) If the time to fall from the top of its trajectory is one second, the height would be 5 meters, or about 16 feet. Again, basic physics: all objects in free fall near the surface of the earth fall 5 meters in the first second.

c) as noted previously, it is hard to tell the exact scale, but I don't think that is a 16 ft high arc.

d) The exact time of its trajectory isn't really that relevant though.

#4 The big question is: what is causing the "strobe" effect?

- I don't think anyone has mentioned the second most obvious source of light in the frame, aside from the sun: REFLECTIONS from the WATER.

- Now, what might be causing a periodic reflection from the water?

>> The waterfall hitting some natural barrier at the base of the water that is periodically moved back and forth by the waterfall, or perhaps a pool of water in a rock that is periodically filled and emptied by the waterfall. The possibilities are endless, and I'm sure we could all imagine numerous other physical phenomena that will produce periodic motion at the base of a waterfall - in this case, periodic motion that results in the reflection of the sun's rays into the air where that drop happened to be thrown into the air.

Simple harmonic motion at the base of a waterfall seems a much more probable event than a strobe assist beam lighting that drop at such a large distance - to me, anyway.

Rather than just guessing and hypothesizing why don't you compare the frequency of the water-drops to the frequency of the AF-Assist beam and see if they match?  You aren't curious

Once the camera had focused and took this shot, there is no further AF assist.  That all happens before AF is locked and the camera will fire. So there is no way the AF assist would be active during the shot -- unless it came from a second camera.  But then the whole waterfall would have the strobe effect.  It has to be something else.

My guess would be sunlight flashes reflected up from water ripples on the pond.  That would be intense enough, directional enough, close enough, and you can get fairly fast ripple play.  Whether that is really the cause I don't know.  But this is a strange anomoly to be sure. I've never seen anything quite like it.

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mailman88
mailman88 Veteran Member • Posts: 6,148
Re: Could it be a rogue water droplet?

....A single water droplet would travel slower than the water in masse. So the water droplet is falling slower than the faster waterfall with the 2 second exposure.

Water almost never travels up before going down. The picture shows the droplet doing this, very strange. Like guess hitting a hard object would force the water up.

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AShimon Contributing Member • Posts: 797
Re: Could it be a rogue water droplet?

mailman88 wrote:

....A single water droplet would travel slower than the water in masse. So the water droplet is falling slower than the faster waterfall with the 2 second exposure.

Your hypothesis ignores the laws of physics. The water droplet falls just as fast as the droplets in the waterfall. The difference is that no other droplet follows the parabolic one (unlike the water going over the falls).

Water almost never travels up before going down. The picture shows the droplet doing this, very strange. Like guess hitting a hard object would force the water up.

Not sure what you're driving at here. Try re-wording this to better explain your thoughts. But to my eyes and experience, there is nothing unusual about the path the water droplet took. It appears to have been caused by a splash from the falls into the pool below. Simple enough to me.

mailman88
mailman88 Veteran Member • Posts: 6,148
Re: Could it be a rogue water droplet?

Once you view the pic at its largest size, you'll see the water hitting the rock base right of center. A singular water droplet will bounce from this rock base. The droplet is traveling up and down like a rainbow, and its speed is slower than the water itself.  The laws of physics apply here and the shutter speed and aperture proves it.

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Jeff Peterman
MOD Jeff Peterman Forum Pro • Posts: 12,890
Re: Could it be a rogue water droplet?
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The speed the water moves to the zenith of the curve depends on the force that made it fly up. But the rate at which it drops is simply dependent on gravity - which will be the same for the droplet and the waterfall.

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mailman88
mailman88 Veteran Member • Posts: 6,148
Re: Could it be a rogue water droplet?

but remember, The droplet itself is smaller and weights less than the water in mass. The waterfall is traveling downward at all times, with one droplet traveling up and then down. Even the water pressure created by the waterfall, would effect the a single droplet. I think the picture captured the moment. A faster shutter speed would have missed it.

This is a good thread on how shutter speed and aperture can actually change the perception of a pic. A creamy waterfall looks much better than freezing the action. Propellers look  better moving than frozen. Sometimes you capture something special, but not expecting the results, the OP did just that.

Its good conservation anyway, just my take.

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AShimon Contributing Member • Posts: 797
Re: Could it be a rogue water droplet?
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mailman88 wrote:

Once you view the pic at its largest size, you'll see the water hitting the rock base right of center. A singular water droplet will bounce from this rock base. The droplet is traveling up and down like a rainbow, and its speed is slower than the water itself. The laws of physics apply here and the shutter speed and aperture proves it.

mailman88, please explain what you are saying again. You are talking about 'speed' of the droplet being slower than the water itself. Meaning what?

I am well-trained in classical physics, and I can assure you the droplet is falling no slower than the waterfall behind it.

2esetters
2esetters Senior Member • Posts: 1,978
Re: Could it be a rogue water droplet?

Well, possibly slower.

The water on the waterfall did not start accelerating from zero if it was fed from a stream which already had some component of downward motion. Additionally, it is unlikely in such a short waterfall that terminal velocity was not reached. Since the falls is higher than the arc of the droplet, would they not have accelerated to a slightly different speed?

Of course, even if true, I don't know how that would create the phenomenon/artifact shown in the photo.

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2esetters
2esetters Senior Member • Posts: 1,978
Re: Could it be a rogue water droplet?
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My only hypothesis is an archer fish with hiccups

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AShimon Contributing Member • Posts: 797
Re: Could it be a rogue water droplet?

2esetters wrote:

Well, possibly slower.

The water on the waterfall did not start accelerating from zero if it was fed from a stream which already had some component of downward motion. Additionally, it is unlikely in such a short waterfall that terminal velocity was not reached. Since the falls is higher than the arc of the droplet, would they not have accelerated to a slightly different speed?

Of course, even if true, I don't know how that would create the phenomenon/artifact shown in the photo.

The vectors involved in the stream's downward motion are equivalent to a 1 degree or less, based on the apparent velocity of the water (judged as the distance between where the water leaves the streambed above and the resulting arc created by the water's motion).

Now, the peak of the parabolic curve is obviously where the droplet vector changes toward the Earth. Acceleration at the same distance from the Earth's center mass affects all objects the same way. In this scenario, a given drop of water at the moment of vector change at the top of the waterfall will fall at the exact same rate as the droplet from its parabolic peak.

The phenomenon is caused, I believe, by a reflection of the sunbeam on the pool below the waterfall. Which is oscillating at a moderately steady frequency. It is the simplest explanation that fits the evidence provided.

dr jim Veteran Member • Posts: 6,645
Re: Strange water formation in long exposure

Clearly there are no fishermen in this group or you'd have figured this out a long time ago. Two possibilities.

First, anyone who has spent much time fishing in small creeks like this (and I have) has seen a small branch caught in water flow, whether it be a little fall like this or a strong current. Commonly, a vibration is set up in the branch that could easily achieve the frequency seen here.  Could be light flashing off a wet leaf or even ripples caused by the vibrating branch.

The second and most likely, is s shiny fishing lure that has snagged and broken off in the stream and is caught in the water flow.  Fishing lures are specifically designed to vibrate and flash as they move through the water. (or in this case as the water moves past them). The flashing attracts the fish.  There is a whole category of lures called flashers. Most of these lures are polished chrome and if it were in the blown out water at the bottom of the falls, it would never show on the image.

Easy. (Sorry this had to come from a Sony shooter whith minimal physics))

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Tim Hutson Forum Member • Posts: 79
Re: Strange water formation in long exposure

I have never considered how the signals from the CCD are sampled by the camera but this photo suggests to me that the droplet effect may be a result of CCD sampling frequency.  The spacing of the droplet seems to be somewhat proportional to the speed a droplet would take in an arc like that.   That is, it is relatively widely spaced toward the bottom of the arc on each side of its apex where its speed is greater.  The closer spacing near the apex suggests a slowing of the droplet which is to be expected.   If the camera does not just bin all of the light intensity until the shutter closes, but instead frequently samples the intensity of the CCD pixels and adds or co-adds the intensities, the images of the droplet (which are pretty bright) would simply register as bright spots in the image each time the CCD signal is sampled and the droplet has moved.

Anybody know if this is the way a time exposure or exposures in general work in today's digital cameras?

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Michel EOS400D SONY DSCV3 Contributing Member • Posts: 872
Re: Strange water formation in long exposure

pfffffft, is this thread still going on ? i must be in the science forum me think

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WilbaW
WilbaW Forum Pro • Posts: 11,595
Re: Strange water formation in long exposure

dr jim wrote:

Clearly there are no fishermen in this group or you'd have figured this out a long time ago. Two possibilities.

First, anyone who has spent much time fishing in small creeks like this (and I have) has seen a small branch caught in water flow, whether it be a little fall like this or a strong current. Commonly, a vibration is set up in the branch that could easily achieve the frequency seen here. Could be light flashing off a wet leaf or even ripples caused by the vibrating branch.

The second and most likely, is s shiny fishing lure that has snagged and broken off in the stream and is caught in the water flow. Fishing lures are specifically designed to vibrate and flash as they move through the water. (or in this case as the water moves past them). The flashing attracts the fish. There is a whole category of lures called flashers. Most of these lures are polished chrome and if it were in the blown out water at the bottom of the falls, it would never show on the image.

The problem I have with these "flasher theories" (as they will be known from now on ), is that the water drop appears to have left no image between the flashes. I would expect to see at least a faint trail along the entire arc of the drop's travel.

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WilbaW
WilbaW Forum Pro • Posts: 11,595
Re: Strange water formation in long exposure

Tim Hutson wrote:

I have never considered how the signals from the CCD are sampled by the camera but this photo suggests to me that the droplet effect may be a result of CCD sampling frequency.

If that were true, anything moving at a suitable speed would appear strobed, but this image shows a distinct exception to that.

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