Did I catch laserbeams in flight?

[Ash]

I shot this video at the Bay Area Laser Enthusiasts Meet last month.
I slowed the video down and backed the frames up to try to figure it out.
+186,000 miles a second, filmed?


Did I catch laserbeams in flight?
I know that it looks like I am seeing the "back end" of the beams. :thinking:

 

[Sigurthr]

Since I'll assume your framerate isn't in the terahertz it would appear to be something to do with the persistance of the camera's sensor pixels? The only thing I can think of is that the beams are moving faster than the clock rate on the CCD, and perhaps it isn't operating in a synchronous mode so you're getting an odd blending/bluring effect; beam turns on and right half sees it but left half hasn't clocked yet so the right half reports it there and the left hasn't and then when the left clocks a fraction of a sec later the beam is off. The controller puts it all together and says there is half a beam.

 

[Things]

This is because the sensor captures each frame line by line. The laser beam was caught in only 1/2 the frame before it disappeared.

 

[Ash]

Hmm,... These sound like relatively adequate explanations.
But I am not totally convinced. :cryyy:

The only thing I can think of is that the beams are moving faster than the clock rate on the CCD,

Maybe. I was using an iPhone4 which uses a CMOS sensor. I'm sure it doesn't make any difference as a CMOS video sensor typically captures a row at a time within approximately 1/60th or 1/50th of a second.

This is because the sensor captures each frame line by line. The laser beam was caught in only 1/2 the frame before it disappeared.

Things: This line-by-line explanation would make sense if the lasers were propagating perpendicular to the CCD (or CMOS) processing direction,

but in this case they were going across, diagonal, horizontal, all-different directions, etc... so I don't know, really.

Things,... are you saying that this would not happen on a high-speed film camera?

Perhaps I will write to Time Warp* and see if we can get some 1,000,000 frames per second shots of this.

*If Time Warp is no longer on TV or doesn't give a shit about this, does anyone have a 1,000,000 frame per second camera that I can borrow or buy?

 

[weeba2kv]

You can read all about this in another thread , this guy asking why the laser beams are stopping asif they really come out and stop , i can't fidn that post right now .

 

[Cyparagon]

This thread.

 

[Ash]

This thread.

Thanks for the link.
But I'm still not convinced that it is purely an effect of the CCD (or CMOS) and shutter speed.

So, to clarify: Will this effect NOT happen with a film camera?: Single picture taken at the "perfect" moment? :thinking:

 

[Things]

AFAIK there is only 1 camera in existence that is able to capture light travelling. There is a video of it on Youtube somewhere. However, even then it isn't really capturing it in a single shot, it fired the laser hundreds of times and gets a frame at different times, each time, until you have a video.

 

[rodman1369]

Don't Question The Magic!

 

[weeba2kv]

ALBERTINO @ 30 ANNI di RADIO DEEJAY // parte 2 - YouTube

 

[ElektroFreak]

Maybe. I was using an iPhone4 which uses a CMOS sensor. I'm sure it doesn't make any difference as a CMOS video sensor typically captures a row at a time within approximately 1/60th or 1/50th of a second.

What you're describing is a commonly seen effect with iphones and some ipads so it seems that the sensors used in those devices are prone to it, and the descriptions here are accurate. Nothing so incredible as a million+ fps camera embedded in your iphone as much as you might like that. This effect is also commonly seen when taking video of fast moving things such as aircraft propellers which are not moving anywhere near the speed of light, in which case the moving object appears to separate into several oddly-shaped sections that seem to slowly scroll along.

 

[Ash]

What you're describing is a commonly seen effect with iphones and some ipads so it seems that the sensors used in those devices are prone to it, and the descriptions here are accurate. Nothing so incredible as a million+ fps camera embedded in your iphone as much as you might like that. This effect is also commonly seen when taking video of fast moving things such as aircraft propellers which are not moving anywhere near the speed of light, in which case the moving object appears to separate into several oddly-shaped sections that seem to slowly scroll along.

Thanks. Yes. I read the thread over at PL. :tsk:

And I've seen the aircraft propeller vid:

No worries. I already have a request in to Time Warp to "borrow" their camera. :wtf:

 

[ElektroFreak]

Ahh well in that case I feel I must sincerely apologize that my ESP skills are lacking.. maybe I'm having an off day.. Speaking of which can you please tell me where I've left my car keys as I've forgotten?

Also, when someone asks a question on LPF, I answer on LPF.. I know that's shocking and all. Your last post HERE indicated that you weren't buying the responses given. Lol.. sometimes people make my brain hurt.

 

[Ash]

Ahh well in that case I feel I must sincerely apologize that my ESP skills are lacking.. maybe I'm having an off day.. Speaking of which can you please tell me where I've left my car keys as I've forgotten? Your car keys are in your pocket. :na:

Also, when someone asks a question on LPF, I answer on LPF.. I know that's shocking and all. Funny, I thought I did answer here at LPF :undecided: and was just referencing the PL thread linked to. Your last post HERE indicated that you weren't buying the responses given. Lol.. sometimes people make my brain hurt.

I didn't mean to confuse you with my ambiguous answers. :yabbem:

I think people are not understanding my question. My question is not about the beams looking like they are going in "slow motion" like the (DeeJay) video you linked to. They don't look slow to me at all in my original (un-modified) video. It's about the "separated" ends of the beams as the laser "fires".

I just want my question answered:

If this is truly an effect of the "CMOS or CCD" limitations, will the "tail-ends" of the laserbeams not be seen by taking a single picture using a Film camera (if taken at the correct moment)?

 

[ElektroFreak]

What you are calling the ends of the beams I believe are just the effect of the sensor refreshing, not actually the backside of the beam traveling away. I think the reason the iphone is prone is because of the refresh method used. Now I can't tell you details about the sensor and how it refreshes so this is just speculation, but given the staggering nature of the response time it would take to actually freeze the tail of the beam in flight (film doesn't respond nearly fast enough) it's the most likely explanation IMO.

 

[LSRFAQ]

Also the MP4 file compression tends to do things like only store some changes in the image from frame to frame. So that is a factor as well. Withot schematics of the camera in question, chip data sheets, and a way to understand the MP4 compression software, we can only speak generally as to what is going on.

If it were a straight up old direct scanning vidicon camera, before CCD, the prop or the moving laser beam is just a blur, because the data came out one pixel at a time.

It is a sampling and software artifact.

The camera might also be sampling each line at a slow speed, we dont know what the exposure time is.

Also most modern cameras only store the "CHANGES" in each image, and use the last few images as seed frames to calculate the next image.

So all sorts of math is going on, making a exact explantion difficult.

Lets look at the airplane prop movie for a possible example.

I can tell you this, that is a constant speed prop, and its moving at ~9600 RPM.
Its ran from a geared down gas turbine. The turbine has its best fuel consumption when it runs near its max speed. They change the pitch angle of the blades to change the thrust and keep the prop spinning the same. This saves much kerosene/jet fuel and makes a easier gear box to build.

The camera is running at max 30 frames per second. So the camera is seeing a couple of passes of the blade per frame exposure time. Your seeing 3-4-5 or more images of the airplane propeller, and the blade moves faster at the tip, hence the curve.

Something simliar is going on with the beam show, and the MP4 compression, showing only some changes and key frames, plus the sampling, is wrecking havoic with the image.

We would need the "theory of operation manual" for that specific CCD/CMOS sensor, and a programming team telling us how they did the MP4 compression, to answer your question 100%. Some times you have to take things on faith alone and use assumptions.

Steve