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Assembly and Operating Instructions for Kits


Operation of the Crossed-Beam Sensor


Assembly instructions for other kits


Click on any photo to enlarge.

Crossed-Beam Sensor

Figure 1

Crossed-Beam Sensor control box


3.5mm cable extender

Figure 3

3.5mm male-to-female stereo cable to connect control box to photogate frame

Nikon MC-30 shutter cable3.5mm cable extender

Figure 2

Photogate frame

Figure 4

Shutter cable with 6-ft extension for camera

(photo shows cable for a Nikon camera)



The Crossed-Beam Sensor detects objects such as small birds that pass through the intersection of two perpendicular infrared beams and triggers the shutter of a camera in response. This allows the camera to be prefocused on the specific region where the object will pass. The control box (Fig 1) houses the electronics that carry out the detection and triggering functions. The photogate frame (Fig 2) is connected to the Gate input of the control box using the supplied 3.5mm male-to-female cable (Fig 3). A shutter cable (Fig 4) with a plug for the camera connects to the Shutter output of the control box. Note that the shutter cable is not provided with either the control box kit or the frame kit and must be purchased separately.


Powering the unit

The photogate frame is powered through its connection to the control box. The control box is powered either with a 9-V battery or an optional AC-to-9V DC adapter. In order to install a battery, remove the 4 screws on the corners of the lid of the control box. Lift the lid carefully to expose the battery holder. Clip a 9-V battery into the battery holder. Then reassemble the box. Note that if a battery is installed but the AC adapter is plugged in, the battery is automatically disconnected internally so that it doesn't drain. If you plan to use the unit for long periods of time, it's recommended that you power the unit with the AC adapter.


When the photogate and flash or camera cables are connected, flip the on-off switch to ON to turn on the unit. The Power LED will light.


Testing and sensitivity adjustment

It's recommended that you test the photogate on an indoor tabletop in a dimly-lit room before setting the photogate up outside.

  1. Connect the photogate frame to the control box using the supplied 3.5mm male-to-female stereo cable.
  2. Turn both the fine and coarse sensitivity knobs to their halfway positions. Power the control box on. The Trigger LED should be off at this point.
  3. Place your hand in the middle of the photogate frame to block the invisible infrared beams. The Trigger LED on the control box should light as long as both of the infrared beams are broken. You can use a finger to accurately locate the intersection of the beams. Note that if the Trigger LED doesn't light, the room lights may be too bright. Either dim the lights or try turning down the Coarse sensitivity until you can get the Trigger LED to light.
  4. Now turn the coarse sensitivity gradually counterclockwise. At some point, the Trigger LED will light even though the beams aren't blocked. From this point, turn the knob clockwise to the point where the LED goes out. This is the position of maximum sensitivity. You can fine tune it by going through the same process with the fine sensitivity knob. Turn it counterclockwise until the LED comes on even with the beams unblocked. Then turn it back clockwise until the LED goes out.

Learning to adjust the sensitivity critically as described above is most important for using the photogate in relatively bright ambient light conditions. As lighting changes throughout the day, you may find that you need to adjust the sensitivity correspondingly. For particularly bright conditions, you may need to turn the coarse sensitivity to 0 and use only the fine sensitivity knob for adjustments. For indoor photography or photography at night, the sensitivity adjustment is generally not critical.


Connecting and triggering a camera, flash unit or wireless transceiver

The crossed-beam photogate can be used to discharge a flash unit or actuate a camera shutter or wireless transceiver. In most applications, though, a camera is actuated and the camera in turn discharges a flash unit. Before connecting a flash or camera to the control box, it's best to have the control box and the flash or camera turned off. Turn on the equipment after you've made connections.


In order to actuate a camera, connect the shutter cable for your camera to the 3.5mm stereo jack labeled Shutter on the control box. In this mode, you can work in ambient light, and your flash discharge will be synchronized by the camera. The response time is affected primarily by the shutter lag of the camera. Turn off as many automatic operations on the camera as possible, as these operations tend to increase the shutter lag time.Also, set your camera so that it doesn't go to sleep. You can try using live mode if your camera has that feature.


In order to discharge a flash unit directly, simply connect the flash unit to the Shutter output using a 3.5mm mono plug. When triggering a flash unit in this way, the response is quite rapid; the delay between breaking the beam and the start of flash discharge is less than 50 microseconds. Use this mode when you need the fastest possible response and you can work in a very dark environment. The reason for the latter is that you would need to keep the shutter of the camera open on bulb in readiness for the flash discharge. Caution: If your flash unit has a high-voltage synch circuit (>80 V), don't connect it to the control box as this would burn out the optocoupler. In the event that you do burn out the optocoupler, a replacement part is available here.


In order to actuate a wireless transceiver, connect the transceiver to the Shutter output uing a 3.5mm mono plug. Keep in mind that the use of a transceiver may introduced a delay of a few milliseconds.


Single-beam operation

The typical mode of operation is using two crossed beams with the camera prefocused on the intersection of the beams. However, it's also possible to use only a single beam. This may be used, for example, in photographing small animals feeding on a platform. See the description below. Click on the photos to enlarge.

The ramp, platform, and frame

A platform with a ramp was built for a chipmunk or other small animal to ascend. The photogate frame was positioned so that the horizontal beam passed over the top of the platform. The vertical beam was blocked by the platform. With the vertical beam blocked, the horizontal beam is active along its entire length. Wherever the chipmunk blocks this beam will result in triggering.


Dirt is scattered on the platform to make it look more natural, and sunflower seeds are scattered on and around the platform.

Camera and flash position

This view shows the position of the camera, which is mounted on a short tripod about the level of the platform. The ambient lighting was subdued due to clouds and an overhead deck, so two wireless flash units were used to augment the ambient light. The flash units were set to 1/4 power, shutter speed to 30 or 60, aperture between f/22 and f/32 for good depth-of-field.

Chipmunk feeding on the platform

A chipmunk is captured with a sunflower seed. The set up can also be used to photograph small birds that prefer to feed on the ground rather than from a platform feeder.


Note that if one wanted to use double-beam operation for the set up above, one could drill a hole in the platform at the appropriate place to allow the vertical beam to pass. In this case, the active area would be the intersection of the two beams, allowing more precise positioning of the subject for the photo.


Double-beam operation

A typical setup is described below


Setup of the frame and lights

  1. Before mounting the frame, the flight paths of birds to the feeder were observed. Then the frame was mounted to maximize the number of birds passing through the frame.The photo shows the frame mounted to a pole with clamps. Alternative methods of mounting include tape or hook and loop fasteners.
  2. For this photo, the camera was mounted on a tripod far enough away to show most of the seup. In actual use, the camera would be moved close enough to limit the field of view to the area within the frame.
  3. The camera was focused on a plumb bob hanging slightly in front of the frame. Choosing a location in front of the frame helps to account for shutter lag time, as hummingbirds can travel a significant distance after passing the intersection of the IR beams.The decision where to focus is a matter of informed trial and error. Using a small aperture, f/22 for example, provides greater depth-of-field.
  4. The photogate frame was connected to the Gate input of the control box, partially seen at the bottom of the photo. The Shutter output was connected to the camera, and an AC/DC adapter wais connected for power. In this case the sensitivity knobs were turned low due to the ambient light level. The Coarse sensitivity was set between 1 and 2 and the Fine sensitivity at 5.
  5. Two flash units were positioned close to the frame on either side of it. For convenience, the flash units were actuated wirelessly by the camera, although they could have also been actuated through PC cords. For this shot, a Nikon D700 in remote commander mode was used with Nikon SB600 and SB800 Speedlites. The Speedlites were set to 1/32 power in order to minimize motion blur.

Testing for triggering

The trigger function was tested by breaking the IR beams with a finger. This was checked occasionally as the ambient light level changed during the shoot.

First hummingbird photo

A rufous hummingbird passed through the gate shortly after setup was complete. The fact that the bird is off center is a result of shutter lag. The bird moved a significant distance between triggering and opening of the shutter. In this case, the bird was moving parallel to the plane of the frame and is therefore in acceptable focus.


Hints for successful operation

  • Set your camera for complete manual operation. Turn off any lens VR control. The fewer operations your camera needs to perform before opening the shutter, the faster it will respond (shorter shutter lag).Also, set your camera so that it doesn't go to sleep.While a bird passing through the gate would wake up the camera, the shutter wouldn't be activated until the next passage.

  • If you photograph outdoors, set up in an area that will be shaded throughout the day if possible. Use a shade if available.

  • If you're going to leave the gate set up for long periods of time and are within reach of an AC outlet, power your devices with AC/DC adapters.

  • When the light level goes down and the sensitivity drifts, your camera may take a large number of shots spontaneously or it may not take any pictures at all. Monitor your set up closely whenever the ambient light level is changing significantly and adjust the sensitivity accordingly.

  • Use a small aperture to increase depth-of-field. Flying birds and insects will quickly move out of the plane of the gate after triggering. Your camera's shutter lag, even if small, is still large enough that some subjects will leave the area of sharpest focus before the shutter opens.

  • Use more than one flash unit both to balance the lighting and also to provide more light on the subject. Use your units on low power in order to freeze wing motion. Set the flash units so that they don't power off automatically after a certain period of time.

  • The background will be dark even in daylight conditions if you're using a small aperture. If you want the background to show, reduce the shutter speed. This will take some trial and error. If you reduce the shutter speed too much, the subject will show ghosting as a result of movement. Something else you can try to bring out the background if it's not too far away is to use a flash to illuminate the background only. If the background is far away, you can hang your own background. Then you can set your camera for the fastest shutter speed that will synch with your main flash.

  • Finally, be patient. In many of your shots, the subject will be cut off by the frame, out-of-focus, or in an uninteresting position. If you get a few good shots per shoot, that's par for the course.

For more information on shooting using the Crossed-Beam Sensor and frame, see the articles below.



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