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Copyright 2010-2015
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Last update : 2020/09/05

Barrier detector for laser photography.

This small electronic assembly is a complement of the lightning detector.
It is simply composed of a photoresistor.
The principle of this plug-in is to detect the failure of the laser beam
when passing an object or a subject, which is transmitted to Lightning Detector.
You can use any source of visible light to make a light barrier,
but I preferred to use a laser because the range can be several tens of meters.
The lightning detector triggers the relay when the photocell does not receive the laser beam.
You can adjust the sensibility of lightning detector to detect any failure of the laser beam.
The relay permit to control the DSLR camera with the remote control from the camera.
For more details on the lightning detector and its implementation,
please refer to the "Lightning Detector" in the "Tips and Tricks".

The electronic assembly is visible on the photo01.
To perform the laser detector will require just a photoresistor and
a box or tube. I chose a photoresistor in TO18 format, and integrate it directly
in a jack (photo02). You can use any photoresistor.
Photo03, you can see the photoresistor soldered directly onto the jack and connected to the lightning detector.

Photo04 on, you can see the photocell illuminated by the laser LED.
The advantage of laser red light from a few milliwatts is that the light beam is not visible
and therefore will not interfere in the photograph.

The detection of the failure of the laser light takes a few milliseconds.
Each digital DSLR camera at a time trigger different, for my Nikon D90 the
time is approximately 100 ms.
Thus the detection of an object or moving subject takes a few milliseconds but takes the
photo with my Nikon D90 takes about 100 ms. If the subject is moving at a speed of 8 meters per second
then the picture will be taken when the subject will have traveled 0.8 meters.

To test the detection laser beam, I used a quad Playmobil rubbing (Photo05).
The camera is set on low speed (1/15s - 1/40s) to capture the sensation of movement.
The flash was set on the second curtain to freeze the Playmobil at the end of the photo.

The Photo06, Photo07 and Photo08, permit to show that the detection is accurate (always at the same time)
and that the system works very well, day and night.

Copyright 2011 ThierryD -
Last update 03/05/2011
Reproduction prohibited

Use arrows for the direction and speed. Click on thumbnail for enlarge.