Luminous Landscape Forum
Equipment & Techniques => Beginner's Questions => Topic started by: Keith S on January 14, 2008, 10:06:33 pm
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Just to the right of the ice there is a drop of water that travels up in an arch. My question is why does it look like a strobe light was on? This shot was taken in a river with only sunlight. I was using ND filter with a circular polarizer.
(http://img91.imageshack.us/img91/937/mg0753xr2.jpg)
If you have any question feel free to ask.
Thanks, Keith
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I'm going to guess that as it traveled the sun struck it at various angles. Maybe demosaicing and/or noise reduction finished the job.
Complete guess.
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I'm going to guess that as it traveled the sun struck it at various angles. Maybe demosaicing and/or noise reduction finished the job.
Complete guess.
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The long exposure noise reduction was on (1/3 sec exposure). One thing that is interesting is that you will notice the space between the drop deceases as it reaches it's apex then the spacing increases as the drop goes down. This would infer that what ever was highlighting the drop had a specific freq which would explain the spacing change as the drops velocity changed.
Keith
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Very bizarre and interesting.
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The thing is I can probably find a near identical example in my own files. I know I've seen this in some waterfall photos.
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The thing is I can probably find a near identical example in my own files. I know I've seen this in some waterfall photos.
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The shot was taken at 1.3 seconds not 1/3. The only thing I can think of is if the sensor samples the incoming light at a set freq then this may explain it. But if that were true then why are action shots c/w blur not staggered, as in multiple images spaced like the drop in the photo?
Keith
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The shot was taken at 1.3 seconds not 1/3. The only thing I can think of is if the sensor samples the incoming light at a set freq then this may explain it. But if that were true then why are action shots c/w blur not staggered, as in multiple images spaced like the drop in the photo?
Keith
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The only explanation I can think of which holds water is that there are several drops each equally spaced and, because of the motion towards (or away from) the camera the amount of perceived motion is much less than those drops traversing the plane of view. Whether the rock formation and flow of the water are able to produce a regular stream of drops each small, equally spaced and following the same path is open for debate (though I don't see any reason for a strobing effect on a single drop).
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The only explanation I can think of which holds water is that there are several drops each equally spaced and, because of the motion towards (or away from) the camera the amount of perceived motion is much less than those drops traversing the plane of view. Whether the rock formation and flow of the water are able to produce a regular stream of drops each small, equally spaced and following the same path is open for debate (though I don't see any reason for a strobing effect on a single drop).
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The only problem with this concept is that the drops would have to have the exact same mass and velocity. If you look just to the left of the arch you will see another one. Two sets of identical drops traveling at the same speed?
Wierd stuff.
A group of us here at work (not digital photo experts) are leaning towards sensor sampling freq.
Keith
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A group of us here at work (not digital photo experts) are leaning towards sensor sampling freq.
Keith
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(a) sensors don't sample, they accumulate.
( Why does it only affect two drops and not the rest in the image?
If the water is being forced through a hole in the ice then it is not unreasonable for all the drops to be equal size, velocity and production rate. There is plenty of equipment and many natural environments where such situations occur - it's just rare to catch the phenomena in this one.
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(a) sensors don't sample, they accumulate.
( Why does it only affect two drops and not the rest in the image?
If the water is being forced through a hole in the ice then it is not unreasonable for all the drops to be equal size, velocity and production rate. There is plenty of equipment and many natural environments where such situations occur - it's just rare to catch the phenomena in this one.
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Thanks for the info on the sensor that puts that idea to rest.
I agree there are conditions where this can be created as in water canons in a water fountain display. If you look at the photo there is no ice at either end of the drops path. Also, if you blow up the drop you will see that as it is traveling up it looks like it is trying to separate into two drops but at the apex it goes back into one drop since the velocity at the point is zero.
I appreciate the comments.
Keith
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With a slow shutter speed, how can anything such as moving water drops possibly be sharp and not blurred?
Rob C
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With a slow shutter speed, how can anything such as moving water drops possibly be sharp and not blurred?
Rob C
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Here is a shot of a ball being dropped with a 1.3 sec exposure. Notice the blur and no sharp images which is what we would expect.
(http://img248.imageshack.us/img248/1456/balldrophc6.jpg)
Now here is a thought. The river shot had the sun off to the side but not 90 degrees can a circular polarizer cause this??
Keith
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Interesting phenomenon. I'm really intrigued by what might cause it.
I have no insight, but would suggest asking this in one of the other forums. I know I personally rarely visit this forum and to me this is more advanced than a beginner's question.
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What camera model, ISO setting, etc? It looks to me like the camera did the equivalent of taking several high-speed exposures and then blended them to create a strobed effect. The entire image has that look, not just the drop; there is a lot of unusually sharp structure in the moving water that should be a smooth blur. If this isn't the result of some weird in-camera processing the only other possibility is a strobe that produces pulsed output was involved in the lighting somehow. And the bouncing ball test is invalid; the ball is big enough that the successive "frames" of the strobe effect would overlap into a smooth-appearing blur. Try dropping BBs or something like that against a distant, unlit, black backdrop, and drop them from above the frame so they are moving faster.
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Maybe the projectile is spinning, like a water drop with a small flake of mica schist in it, and when the schist is in a certain position, it flashes back at the camera. Or, maybe it's just the optical properties of a spinning drop without a particle.
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What camera model, ISO setting, etc? It looks to me like the camera did the equivalent of taking several high-speed exposures and then blended them to create a strobed effect. The entire image has that look, not just the drop; there is a lot of unusually sharp structure in the moving water that should be a smooth blur. If this isn't the result of some weird in-camera processing the only other possibility is a strobe that produces pulsed output was involved in the lighting somehow. And the bouncing ball test is invalid; the ball is big enough that the successive "frames" of the strobe effect would overlap into a smooth-appearing blur. Try dropping BBs or something like that against a distant, unlit, black backdrop, and drop them from above the frame so they are moving faster.
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I'll try to set that up tonight and also post the camera/photo info.
Keith
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Yes, sensors accumulate charge as photons impinge upon the receptor sites. And then the sensor is read out or "sampled" one line at a time, synchronously. "Synchronously" may be the key here, because it implies the single "specific frequency" that Keith mentions in the thread, above.
This is a single drop of water, following the classic parabolic acceleration curve caused by the force of gravity on a projectile. But how the in-camera processing created it, I do not know. I tend to agree with Jonathan that it is an in-camera composite artifact. However keep in mind that, as regards sensor read-out, a frame is not an atomic entity. Thus, such an in-camera composite as Jonathan postulates might be comprised of only certain pixel rows or portions of pixel rows.
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I'll try to set that up tonight and also post the camera/photo info.
Keith
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Attached is the drop photo information. The camera was set to shutter lock/timer and I was using a tripod (guess that goes without saying). The distance to the water was about 3 feet.
This shot was taken at the same time @ 15 sec f22 the rest of peramiters are the same.
(http://img223.imageshack.us/img223/900/mg0696kd9.jpg)
After 15 seconds I expected the water to be milky white as mentioned earlier.
I'll try to setup the BB shot now.
Keith
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I couldn't find any BB's so I used a 1/4" ball bearing. Image Shack is not allowing me to upload at this time. The shot showed a blur on the way down but it also picked up the rebound off the floor. The rebound was very simular to the water drop shot in arching but it was just a blur with a little more detail at the apex.
just thought to add it as an attachment.....
Keith
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The entire image has that look, not just the drop; there is a lot of unusually sharp structure in the moving water that should be a smooth blur.
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I agree with this ... there is a lot of "detail" and "texture" in what should be very blurred water. It shows in the full image as well. I personally have never seen this with a stream or waterfall, but I don't think I've ever used an exposure longer than 2 or 3 when shooting those.
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If you have any question feel free to ask.
Thanks, Keith
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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?
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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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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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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 ...
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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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That would be my guess too.
Cheers,
Bernard
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Here is a crop if the drop arc.
(http://img266.imageshack.us/img266/4946/dropcropmx8.jpg)
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.
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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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Here is a crop if the drop arc.
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Being new to all this I was experimanting with ND filters and a circular polarizer.
...
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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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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 (http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0469(1991)048%3C2245%3ALMOSRD%3E2.0.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 (http://www.rit.edu/~andpph/photofile-sci/drip_sequence_0076-6a.jpg) (I think I can see some wobble in this drop already! Look at the last two frames)
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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 (http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0469(1991)048%3C2245%3ALMOSRD%3E2.0.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 (http://www.rit.edu/~andpph/photofile-sci/drip_sequence_0076-6a.jpg) (I think I can see some wobble in this drop already! Look at the last two frames)
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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.
(http://farm4.static.flickr.com/3265/2350619079_6b11b78816_b.jpg)
Even in this shot you can see drops as they trail off and caught by the light.
Keith
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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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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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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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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.
(http://farm4.static.flickr.com/3125/2788370800_17cbef0a5e_b.jpg)
ISO100
17mm
15sec @ f/22
Dutch Square, Melaka, Malaysia
Comments?
Thanks, Keith
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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.
(http://farm4.static.flickr.com/3125/2788370800_17cbef0a5e_b.jpg)
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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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)
(http://farm4.static.flickr.com/3632/3649964972_a9c850f15f_b.jpg)
Here is the "streak"
(http://farm3.static.flickr.com/2464/3649965072_866597bed3_o.jpg)
And here is the "strobe" effect
(http://farm4.static.flickr.com/3537/3649161383_99a3ac9b44_o.jpg)
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