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Author Topic: Strobe light?  (Read 32203 times)
Colorwave
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« Reply #20 on: January 16, 2008, 01:37:35 AM »
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If you have any question feel free to ask.

Thanks, Keith
[a href=\"index.php?act=findpost&pid=167213\"][{POST_SNAPBACK}][/a]
I've got nothing but questions, Keith.  Isn't the drop moving almost perpendicular to the water flow?
Would you mind posting a larger crop (or 100% crop) of the drop portion of the image?
Thanks,
Ron H.



UFO reflection?
« Last Edit: January 16, 2008, 01:44:10 AM by Colorwave » Logged

John Sheehy
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« Reply #21 on: January 16, 2008, 07:43:45 AM »
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I agree with this ... there is a lot of "detail" and "texture" in what should be very blurred water.[a href=\"index.php?act=findpost&pid=167474\"][{POST_SNAPBACK}][/a]

Well, that could be explained by very bright specular highlights that are moving.  The level of illumination along their trail stands out against the background.
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Wayne Fox
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« Reply #22 on: January 16, 2008, 12:48:37 PM »
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Well, that could be explained by very bright specular highlights that are moving. The level of illumination along their trail stands out against the background.
[a href=\"index.php?act=findpost&pid=167528\"][{POST_SNAPBACK}][/a]

But it would seem that several of the somewhat sharp streaks, in a moving stream, are only about a second or so long- much too short for a 15sec exposure ... when photographing moving water specular highlights are all over the place and in 15 seconds would pretty much blur together.

Thinking this through, one thought has crossed my mind, having to do with specular highlights.  How do you take a 15second exposure in what appears to be somewhat direct lighting - a lot of ND?  Is it possible that a polarizer or even multiple polarizers (such as Singh-Ray's variable ND filter) was used to add neutral density, and the construction and design of the polarizer is causing this affect on specular highlights?  Just a crazy thought ...
« Last Edit: January 17, 2008, 10:53:31 AM by Wayne Fox » Logged

BernardLanguillier
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« Reply #23 on: January 19, 2008, 05:01:37 PM »
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Maybe the projectile is spinning.
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That would be my guess too.

Cheers,
Bernard
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A few images online here!
Keith S
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« Reply #24 on: January 19, 2008, 06:35:18 PM »
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That would be my guess too.

Cheers,
Bernard
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Here is a crop if the drop arc.



Being new to all this I was experimanting with ND filters and a circular polarizer. To get the 15 sec exposure I used a 4X + 8X Hoya ND and a B+W circular polarizer. Personaly I think this is caused by the polarizer or in combination with the ND filters.

I also sent this to Canon for review. They came back with this....

"Thank you for your E-mail inquiry regarding your EOS 5D digital camera.

After reviewing the images you have provided I am having difficulty seeing a problem with the camera.  To insure that the arch in the first photo is not caused by water droplets you may want to provide some other samples with no water.  A photo outside on a sunny day and a photo at night.  Please forward the samples when you get a chance to send them to us. Also please forward some more sample photos with the water at faster shutter speeds."

I realize that it may seem like I am fixating on this but finding root causes is what I do for a living.


Thanks for all the input

Keith

Edit- just to keep things straight, the arc shot was 1.3 sec, the other full shot was at 15 sec.
« Last Edit: January 19, 2008, 06:38:34 PM by Keith S » Logged

je1330
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« Reply #25 on: February 09, 2008, 09:51:46 AM »
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Hi, I have two questions that I didn't notice in here so far...

1.)  Might the area in the picture have been under mottled light, such as from a tree full of leaves?  I could almost see the drop moving in and out of the light and producing that sort of image, but the gradual seperation between the dots would mean it would have to be a very precise pattern of mottled light.  So, I guess there went that theory.

2.)  My second thought, is are you absolutely positive it's a drop of water?  You'd be the one to know, but did there happen to be anyone near you when the picture was taken, maybe throwing rocks out at the ice to break it?  My thought is possibly a rock or something thrown in a curve up and outward and spinning so that it caused flickering light-flare in the lens as it went.

It would be quite a coincidence, but I believe it's certainly possible.  Of course, if you were alone, it's not.
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AndyF2
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« Reply #26 on: February 10, 2008, 10:25:55 PM »
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Here is a crop if the drop arc.
...
Being new to all this I was experimanting with ND filters and a circular polarizer.
...
[a href=\"index.php?act=findpost&pid=168269\"][{POST_SNAPBACK}][/a]
In your first photo, it looks like something splashed into the water.  There are three sprays coming up.  The dotted arch may be a piece of ice thrown up from that splash.  It wouldn't be rotating (hard to see where a spinning force would have been applied to it), but it could be tumbling while going up and falling down again.  The polarizer may make the difference between reflecting and not reflecting more extreme.
In your second photo there's another one but this is going straight up, or down.
A nice puzzle! Maybe that's the explanation.
Andy
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PTeeCee
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« Reply #27 on: February 27, 2008, 09:32:23 AM »
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Interesting problem. I suspect that it is due, somehow, to reflections off the surface of a droplet of water that is undergoing a harmonic oscillation in shape, i.e. the drop is not continuously spherical but is isovolumetric of course. The drop wobbles alternately elongating and shortening (for the want of a better description) rhythmically as a result of the combination of surface tension effects and the forces applied to the water that resulted in the generation of the drop. This application of force may be relatively great (the drop appears to be traveling at a high angle to the general flow of the water in the stream) and the resulting oscillation more pronounced.

I am making some guesses here. It is not my area but a quick Google search does pull up some suggestive scientific paper titles, including  "Laboratory Measurements of Small Raindrop Distortion. Part 2: Oscillation Frequencies and Modes" http://ams.allenpress.com/perlserv/?reques...2.0.CO%3B2&ct=1

Ultimately in theory if the drop were to travel undisturbed for long enough it would be become more and more spherical with internal friction progressively dampening the oscillation.

Having said all that I am assuming that at some particular stage in the cycle of the changing shape a surface forms that reflects light most effectively at the camera to give a specular highlight.  Where is Harold Edgerton when you need him? http://www.rit.edu/~andpph/photofile-sci/d...nce_0076-6a.jpg  (I think I can see some wobble in this drop already! Look at the last two frames)
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Keith S
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« Reply #28 on: March 27, 2008, 11:14:44 PM »
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Interesting problem. I suspect that it is due, somehow, to reflections off the surface of a droplet of water that is undergoing a harmonic oscillation in shape, i.e. the drop is not continuously spherical but is isovolumetric of course. The drop wobbles alternately elongating and shortening (for the want of a better description) rhythmically as a result of the combination of surface tension effects and the forces applied to the water that resulted in the generation of the drop. This application of force may be relatively great (the drop appears to be traveling at a high angle to the general flow of the water in the stream) and the resulting oscillation more pronounced.

I am making some guesses here. It is not my area but a quick Google search does pull up some suggestive scientific paper titles, including  "Laboratory Measurements of Small Raindrop Distortion. Part 2: Oscillation Frequencies and Modes" http://ams.allenpress.com/perlserv/?reques...2.0.CO%3B2&ct=1

Ultimately in theory if the drop were to travel undisturbed for long enough it would be become more and more spherical with internal friction progressively dampening the oscillation.

Having said all that I am assuming that at some particular stage in the cycle of the changing shape a surface forms that reflects light most effectively at the camera to give a specular highlight.  Where is Harold Edgerton when you need him? http://www.rit.edu/~andpph/photofile-sci/d...nce_0076-6a.jpg  (I think I can see some wobble in this drop already! Look at the last two frames)
[a href=\"index.php?act=findpost&pid=177705\"][{POST_SNAPBACK}][/a]

Been gone for a while
I agree, this drop was oscillating. This would explain the "strobe effect" as it changed it's shape and caught the light. I have since taken this photo which was taken around .5 seconds.



Even in this shot you can see drops as they trail off and caught by the light.

Keith
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DiaAzul
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« Reply #29 on: March 28, 2008, 06:01:32 AM »
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Ultimately in theory if the drop were to travel undisturbed for long enough it would be become more and more spherical with internal friction progressively dampening the oscillation.

Entropy - the motion would be converted to heat and the drop of water would warm up. Eventually all the energy which is driving the oscillations would be converted to heat => warm up the droplet and the droplet would assume the steady state form which is the sphere. Thermodynamics not internal friction.
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David Plummer    http://photo.tanzo.org/
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« Reply #30 on: March 29, 2008, 12:07:49 PM »
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Thermodynamics not internal friction.

Internal friction would be the process by which the oscillation of the water droplet is converted to heat...
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nhnus
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« Reply #31 on: April 20, 2008, 09:38:49 AM »
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It's well know in the "Cloud Microphysics" discipline that raindrops oscillate as they fall.  (There's at least one paper by Ken Beard in the late 60's early 70's showing photographs of falling drops oscillating.)  Now when you combine that information with the fact that the scattering of light by "small" particles is strongly directional, I think you've got the most probable explanation for your phenomenon.  You see the drop when it's shape is oriented in particular direction with respect to your camera.  By the way, it's really cool that you've got the entire trajectory including the initial fall and the bounce off the water surface.  (Why it bounces is another mystery.)
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Keith S
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« Reply #32 on: August 28, 2008, 12:08:10 AM »
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A friend of mine took this shot. When I first viewed it I thought OK HERE WE GO, I have proof that the sensor receives light at a set frequency! After taking time to think about it I believe the answer is that a light bulb using AC power has a frequency of 60 hz (cycles per second). This is why the light streak is broken up into segments.
The technique he used was to have a shutter speed of 15 seconds and at the last second he would pick up the camera and move it around. This resulted in the background being in relative focus.





ISO100
17mm
15sec @ f/22

Dutch Square, Melaka, Malaysia

 

Comments?

Thanks, Keith
« Last Edit: August 28, 2008, 01:01:28 AM by Keith S » Logged

BruceHouston
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« Reply #33 on: August 28, 2008, 03:00:26 AM »
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A friend of mine took this shot. When I first viewed it I thought OK HERE WE GO, I have proof that the sensor receives light at a set frequency! After taking time to think about it I believe the answer is that a light bulb using AC power has a frequency of 60 hz (cycles per second). This is why the light streak is broken up into segments.
The technique he used was to have a shutter speed of 15 seconds and at the last second he would pick up the camera and move it around. This resulted in the background being in relative focus.

ISO100
17mm
15sec @ f/22

Dutch Square, Melaka, Malaysia

 

Comments?

Thanks, Keith
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Several thoughts:

(1) The plausability of your hypothesis depends in part on the type (technology) of the light sources.  An incandescent bulb takes much more time to start and stop emitting light than the 10 ms period of a one-half cycle on/off period of a 50 Hz power source (I say 50 Hz because most of the world is on 220v. 50Hz).  However, other light sources react more quickly to the AC power on/off transitions, notably LEDs, etc.

(2) You could easily test your idea by doing a more controlled exposure for 1 or 2 seconds and moving the camera in a more controlled pattern, then counting the segments in a light path to determine whether the number sums to 100 (100 half-cycles at 50 Hz for a one-second exposure).  I did this roughly for the thickest orange light path in the foreground; it appears to sum to around 100-110 segments.

(3) There certainly are frequencies (time windows) associated with imaging sensor operation, including enabling the sensels for reading, a capture (integration) window, and a readout window.  These windows differ for different technology sensors and whether or not a mechanical shutter is part of the imaging system.  In some systems, for example, integration and readout are done one sensel row at a time.  For more information, see:

[a href=\"http://www.isgchips.com/pdf/Shutter_Operations_Kodak_App_Note.pdf]http://www.isgchips.com/pdf/Shutter_Operat...ak_App_Note.pdf[/url]

Best,
Bruce
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Keith S
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« Reply #34 on: June 22, 2009, 01:55:12 AM »
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I knew that if I continued to take flowing water shots this would happen.
   Took this shot this weekend while going for an abstract flowing water shot. Here is the shot where there are "streaks" and the "strobe effect" anomalies in the same capture.
Here is the shot

exif
 Exposure: 0.067 sec (1/15)
Aperture: f/11.0
Focal Length: 66 mm
ISO Speed: 200
(CP + 8XND)






Here is the "streak"






And here is the "strobe" effect





With exposure time being 1/15s there is no doubt in my mind that the "strobe effect" is an oscillating drop of water catching the light and the "streak" is a single drop moving on one plain.

Keith
« Last Edit: June 22, 2009, 02:07:23 AM by Keith S » Logged

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