Reproducing the Velador Experiment

The camera cell and laser cell are best installed during final assembly of the support beam, at a point where there are three walls of the support beam secured in place but the last wall of the support beam has not been added.  I'm saving the support beam's top board for last, because it's the only one with through-bolted fasteners, and thus the only one that can't lie flat when assembled.  It's easier to assemble the beam in two board corner angles rather than screwing one board at a time onto the main beam, then assemble the two angles to form a completed support beam, but this would prevent direct access to the laser and camera cells, which would make sighting in difficult.  So, it's best to make a small concession to side mounting and leave the top board off until coarse adjustment of the cells is complete.  (Note that one side of the beam wall is higher than the other in these photos of the beam under construction.  This is a consequence of the cross-section used.  The missing top board is placed to fill the gap and create a square profile.  Note also that the cell mounting brackets will fit entirely inside the assembled beam.)

The laser cell is installed with the springs set solid.  3/4" wood screws are used to secure the bracket ends as shown, with a 1/8" average gap between the beam and backboard.  The adjusting nuts can then be let out, each by the same number of turns, to reach an adjustable range.

The laser can be mounted in the cell at this time.  I had already mounted the camera in its cell before installing the cell, although I did not yet have the filter in place.  I plan to use a paper screen as a filter, but this is a variation from Osadchey's original design and its performance must be tested first.  I plan to run a short series of tests to check for the best filter type and relative position.  Alternatives include polarizing filters and using the laser off axis.  (Note that the diffuse light of the laser diode is clearly visible in the construction photo, even though the laser is not aimed at the camera.  This light will be detectable inside the beam as well, even when the laser and camera are not aligned, and will have to be checked to see if its image exhibits the same behavior as the coherent laser light.  This also suggests the use of an LED as a cheaper alternative to a laser diode, but that would prohibit examination of thermal refraction as an error source because of the significantly smaller image.)