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Author Topic: Strobe light?  (Read 31793 times)
Keith S
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« on: January 14, 2008, 09:06:33 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.



If you have any question feel free to ask.

Thanks, Keith
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DarkPenguin
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« Reply #1 on: January 14, 2008, 09:21:02 PM »
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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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Keith S
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« Reply #2 on: January 14, 2008, 09:35:23 PM »
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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.
[a href=\"index.php?act=findpost&pid=167216\"][{POST_SNAPBACK}][/a]

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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jjj
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« Reply #3 on: January 15, 2008, 09:41:25 AM »
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Very bizarre and interesting.
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DarkPenguin
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« Reply #4 on: January 15, 2008, 09:59:40 AM »
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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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Keith S
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« Reply #5 on: January 15, 2008, 10:37:12 AM »
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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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DiaAzul
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« Reply #6 on: January 15, 2008, 11:44:29 AM »
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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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Keith S
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« Reply #7 on: January 15, 2008, 12:16:24 PM »
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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).
[a href=\"index.php?act=findpost&pid=167353\"][{POST_SNAPBACK}][/a]

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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DiaAzul
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« Reply #8 on: January 15, 2008, 12:32:20 PM »
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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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David Plummer    http://photo.tanzo.org/
Keith S
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« Reply #9 on: January 15, 2008, 12:44:07 PM »
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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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Rob C
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« Reply #10 on: January 15, 2008, 01:52:19 PM »
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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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Keith S
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« Reply #11 on: January 15, 2008, 02:56:15 PM »
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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.



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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Wayne Fox
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« Reply #12 on: January 15, 2008, 03:30:02 PM »
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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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Jonathan Wienke
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« Reply #13 on: January 15, 2008, 04:38:42 PM »
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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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John Sheehy
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« Reply #14 on: January 15, 2008, 05:11:02 PM »
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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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Keith S
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« Reply #15 on: January 15, 2008, 05:13:03 PM »
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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.
[a href=\"index.php?act=findpost&pid=167414\"][{POST_SNAPBACK}][/a]

I'll try to set that up tonight and also post the camera/photo info.

Keith
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BruceHouston
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« Reply #16 on: January 15, 2008, 06:35:03 PM »
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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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Keith S
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« Reply #17 on: January 15, 2008, 07:24:52 PM »
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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.



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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Keith S
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« Reply #18 on: January 15, 2008, 10:15:56 PM »
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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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Wayne Fox
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« Reply #19 on: January 16, 2008, 12:59:28 AM »
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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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