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A project log for Mechanical Laser Show

device that projects a pattern by quickly moving a laser. all mechanical, 3d printed, hand powered

Evan StanfordEvan Stanford 06/13/2017 at 20:380 Comments

(See the video in the project details. Sorry about the ending.)

Filming the mechanical laser show presented 2 challenges- exposure and focus.

Exposure:

Photographing the POV effect is easy. Just set the exposure to over 1/5 second. Filming the POV effect is challenging. At 30 fps, each frame can have a conceptual maximum exposure of 1/30 second. Since your computer monitor is much dimmer than a laser, it does not create the full POV effect. Therefore in order to display the laser pattern like it is perceived in real life, I applied an After Effect called Echo. This effect merges the current frame into the N next frames, each time fading a predefined amount. This simulates what a human sees when a laser is moved quickly- a path that fades in about 1/5 second.

To further complicate things, my camera cannot actually take 1/30 second (= 33 ms) exposures while filming at 30fps. The camera needs time to read and clear the sensor before starting the next frame. In reality that takes around 3ms, leaving me with only 30ms exposures for each frame. That might not sound like much loss, but during that time part of the path was traced and it was not recorded by the camera. That results in false gaps in the video of the pattern. I did not attempt to fix this for the video.

Focus:

The laser show projects at a very small angle and therefore must be far from the projection surface in order to make a decent sized pattern. When filming both at the same time, the device must be much closer to the the camera than the pattern. With the required low light conditions is was near impossible to get both items in focus at the same time. See Hyperfocal distance . Therefore, in order to make both parts of the shot more closely match reality, I filmed it twice at 2 focus levels and combined the results in post. The Echo effect was only applied to the laser pattern part. Please see the below video for a raw, untouched version. Note that the laser point is out of focus which causes it to look much larger




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