Pasco AP-8210A Camera Option

The “Millikan Oil Drop Apparatus” device from Pasco (Part Number:  AP-8210A) is used in our Modern Physics lab.  The device works very well and gives excellent results.  It was the object of a light source upgrade in 2021 replacing the original incandescent bulb with several LEDs.  Under consideration now is a way of attaching a camera to the viewing telescope so that the live image can be saved as a movie for offline data analysis.

The viewing telescope is the tube part of the machine toward the bottom of the picture at the right.  Because the telescope contains a number of elements, the goal of this project is to leave the telescope unchanged so the system can be used normally if desired.  The camera will be fitted to the end of the telescope.

The camera selected was the “ALPCAM USB 8MP 2-12mm”.  It was selected because the 8MP sensor by Sony is of reasonable size, the focus is manual, the lens has zoom (2-12mm), and the lens is attached by a CS mount.  The included 2-12mm lens has three adjustments on it:  focus, zoom, and aperture.  For this application, the aperture is always full open.

Initial Camera Results

For initial testing, the camera was set directly in front of the telescope.  The typical image is shown at the left.  The illuminated area doesn’t fill the screen and shows about 3x3 big blocks.  Since the area of view is so small, it is very difficult to see enough oil droplets.  

This is a lens problem.  If the lens is zoomed in, the 3x3 blocks are larger but the field of view isn't increased.  Replacing the 2-12mm lens with the longer 5-50mm lens allows more of the image to be filled with the illuminated grid. Unfortunately with the stronger zoom, only 2x2 of the big blocks are visible.  The conclusion is that the 2-12mm lens is the best one to use, it just needs to be closer to the telescope.

Lens Modification

To get the camera closer to the telescope, the solution was to cut the lens hood off the 2-12mm lens using the lathe.  Both ends of the lens were covered with blue painters tape while doing the cutting so metal pieces didn't get into the lens.  The cut was centered on where the outer screw is attached.  Half the cut was done with the lathe bit and then the cut was finished with the cutoff tool.  

The rough edges were carefully trimmed using the deburring tool.  Then the lens was reattached to the camera and positioned in from of the telescope.  The results are much better with 4x6 large grid squares now visible.  

Final Configuration

The final step was to 3d-print a TPU foot and shroud to hold the camera in place at the telescope.  The shroud was printed with dimensions so it fits tightly to the camera on one end and tightly to the telescope on the other.  The TPU foot slides over the camera post and allows some vertical adjustment.  The completed system is shown in the picture below.