Very strange result with 350D

accidental shots are great aren't they?

How about the fact that the water drop is a non rigid free body? It is a mode of vibration (hence the steady period) due to the exchange of energy between surface tension and kinetic energy
When the drop jumps out of the water it is stretched out. Surface tension tries to pull it into a sphere (least surface area) and in the process gives the back of the drop a velocity relative to the front. Then it overshoots the spherical shape and goes flatish. Again the surface tension tries to pull it into a sphere. But it overshoots... and so on.
So the changing shape is reflecting sunlight at regular intervals. If the drop's journey lasted longer the motion would eventually dampen out.

It's a very common sort of phenomenon, but capturing it like this is very special. Nature and physics at its best (well, pretty good anyway).
It's a nice change to see an interesting topic.

The miniscus of the droplet - that is the 'skin' of water held together by the cohesion of the water molecules - is altering shape harmonically, ie stretching into a shape that diffracts light to the camera lens in a rhythmic manner. Think of it as a very thin balloon, changing shape because of the momentum of water inside it...

Very neat capture!

I am new here, and just a beginner, but I humbly suggest that the branch and the drop image are related.

Is the sun coming from the right in the picture? If the branch was moving because of a breeze, it could be moving up and down in a rhythmic pattern. This rhythmic pattern of the branch intermittently blocked the sun's light on the drop, causing the stroboscopic effect.

Good explanation MiG82, I think you may be right. I initially thought that there could be a continuous stream of droplets being deflected by that branch, like someone else mentioned, but then if you look at the 'pattern' the gaps between the droplets increase as it's falling down due to gravity, the push/pull force you mentioned, etc. Now I'm not even close to having a physics major, but if there were more than just one droplet wouldn't the pattern stay constant throughtout the frame?

Even if there's a periodic shape change, which would imply that surface tension was a stronger force than the basic acceleration of the droplet(s), it wouldn't cause the water droplet to cease reflecting light; at best there'd be a diminution of the light, rather than a series of discrete "pulses".

Totally agree with MiG82.

You partially answered your question. The droplet speed keeps rising due to gravity, starting from the top of that curved path. So the distance between the "flashes" would grow too.

Thanks all for your explanations and hypothesis.
I noticed that I had captured this strange phenomena when reviewing the pictures on my computer.
Next time I'll go back there to do more experiments.
I like very much the theory of the droplet changing shape and reflecting the light periodically.
Rgds
Jose

Neat accident, jose. Bet cha can't do it again. It will be different even if you can get close.

Very true, Jon. And it also doesn't explain the "multiple exposures" of the branch either. I'm sure the branch isn't fluctuating in shape from its surface tension.

No. The gravity has no effect on the shape because it acts on every molecule equally. The effect of gravity is to have every molecule follow a parabolic path. The effect of surface tension and small scale momentum are superimposed on this motion.
An excellent example of the very effect we're talking about are videos from the vomit comet, the ISS and the space shuttle. They have messed around with blowing and releasing liquids and you get this exact effect happening. The blobs of liquid vibrate in their natural modes. Don't forget that in these cases there is plenty of gravity (more than 95% of earth surface gravity IIRC) , but the whole scene is in freefall, just like our water drop.

It would be total internal reflection at work rather than diffraction (which is very different to reflection and refraction).


It is extremely unlikely that it is the branch casting shadows because the "shadows" are too regular. If you ran a giant comb through the path of the sun it could happen, but that's assuming the drop is always reflecting into the lens.

Hey there.... Just took this photo with my 20D and found the same thing.

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Please could you post a 100% crop of that section for us to see?

_SBradley_ wrote:
Please could you post a 100% crop of that section for us to see?

Yes, and also the exif data if possible.
Neat picture by the way.
Jose

_SBradley_ wrote:
Please could you post a 100% crop of that section for us to see?

The full picture and exif are here on my gallery. I have to say I was surprised when I found this strange effect.

EOS 20d
LENS EF 85MM f/1.8
ISO 100
F/16
Shutter speed 8sec