Recently I've been going "viral" with videos of concerts where the laser seems to defy the laws of physics. I see this often enough that it's worth writing about, although the technique is nothing new.
So we see the singer and the laser falling on him from above. The beam seems to wrap around the singer like a dancer's sash. The envelope will drop for everyone, but the uninitiated may think - "Mother of God, what in the world is going on". And well it is happening and cars are already flying too. Only that it's not practical because you need a runway.
They are cheating my eyesight!
The technique in question is called LASER BANDING. Although the phenomenon itself is also called ROLLING SHUTTER. And it is an effect that can only be seen on camera. You may have seen a video where the rotor wings in a helicopter stand still, and the helicopter looks like it is levitating.
This is due to the setting of the number of recorded frames in the camera. In the case of a laser, the camera captures only part of the emitted light .
Explanation of the phenomenon
There is one reasonably good explanation on the net, the author I do not know, because everyone pastes it on various English-language forums. It seems to make sense to me. The author is brad1775:
Here's how it works: "If you project a line that moves back and forth, 32 times per second, using a camera that captures only one frame every 1/30th of a second, you will see a pattern that oscillates back and forth every 15 seconds (32/30 = 1 with a reminder of 1/16, resulting in 16 seconds). Lasers, of course, use much faster drawing patterns than 26 "lines" per second. This can allow for a range of co-current timing. If you notice that the ceiling-mounted device was casting several patterns, you will see that the device was capable of outputting several patterns at once, since it can draw 50,000 points per second, with a vector between the points."
(EDIT. Dominik: Nothing kur.... I didn't understand, fortunately below is simpler...)
In simple terms
In simpler terms. The effect involves manipulating and tuning the shutter so that the laser beam looks like this levitating helicopter. Except that in this case, the laser beam needs to be slightly faster so that it leaves a streak behind it, which gives the desired effect
It is worth adding how the laser scanning speed is measured, i.e. kpps. This is the unit that determines the speed of the projector's galvanometers and stands for kilo point per second.
*1kpps = one thousand points per second.
For graphic design, the recommended speed is 25kpps.
Why does the camera flicker?
By the way, I will also briefly touch on the topic of PAL and NTSC video formats, since it is somewhat related to our divagations. Why does the light blink in our cameras? It is related to the fact that in Poland and Europe in general, the electric grid has a voltage frequency of 50Hz, while in the US it is 60Hz.
They have an NTSC system and their stable recording speed is 60fps. Our European camcorder should be set to 50fps or two times less 25fps or two times more 100fps. This setting will guarantee a stable image. In most cameras we will find in the options the possibility to change between PAL and NTSC. If we don't have such an option we can do it with the shutter speed setting in this case to 1/50.
This is so in the form of an addendum to the topic of blinking and deception of vision - but maybe it will help someone if they want to record something for themselves.
