Sunday, March 20, 2011

Stroboscope



Materials:
•1.5” cardboard tube (we got ours from www.uline.com : S-5816, 1.5’’x36’’ kraft mailing tubes, but aluminum foil tubes would work just as well)
• foam core
• black mat board
• straw
• chopstick (that will fit in the straw)

Tools:
• fine tooth saw
• box cutter
• hot glue gun
• large scissors
• compass, straight edge 


Cut the eyepiece (3”) and the handle (6”) out of the large cardboard tube. Cut the two slots in the top of the handle, approx. 1” long and as wide as your foam core. Next, lay out the shutter disk using a compass and straightedge, the disk should be 6.5” in diameter with a small hole in the center and should have a least one radial 2”x.25” slot.  If you are making multiple stroboscopes we’ve found it useful to make one perfect template that can be traced onto other pieces of mat board. If you make a 90 degree cross on the center of your disks, a one slot template can be used to trace disks with one, two and four slots patterns.  A one slot disk will have a typical strobe light effect and is good for looking at people but will not be very effective at making fast moving objects appear still. Two and four slot disks work well for making rapidly moving (spinning or reciprocating) objects appear still, but do not work well for slower moving objects like people. Finally, cut out a foam core eye piece holder, a 2.5’’x3’’ rectangle with a semi circle the size of your I piece tube cut out of one of the short sides.  Mark the hole for the straw in the foam core  about 1.25’’ from the edge of the eyepiece cut out and in the middle height wise. You can check that the hole is in the right place be placing the center of the shutter disk over your mark and seeing if the slot completely clears the cut out in the eyepiece holder. Again, once you’ve made one of these they can be traced as these pieces do not need to be exact. You will also need two approx. 1.5” foam core washers, these can be circular or square with a hole the size of your chopstick/ straw in the middle.






After all your major materials are prepared it’s time to begin assembly.  Hot glue the eyepiece holder to handle so that the middle of the handle is directly under the hole mark in the eye piece holder.  Next, hot glue the eyepiece in place with 2” on one side and 3” on the other side of the holder. Note that you will look into the long side of the eyepiece so which side you choose to leave long will determine if you make a right or left handed stroboscope. Finally, cut a approx. 2’’ length of straw, use a nail to punch out the straw hole and then a pencil to stretch it so your straw fits snuggly.  Put the straw in the hole so that it clears the eyepiece on the short side and does not clear the long side by a good measure as seen above.  If the straw fits tightly use a small amount of glue to stick in place (too much glue can melt the straw).  If the straw fits loosely you may want to glue on a small foam core washer to shore it up (as seen with the shutter disk washer mentioned later).    




 


Next, create the shutter disk assembly. Put your disk and a washer on your chopstick. Insert the chopstick into the straw with the disk and washer on the short side of the eyepiece, and adjust their position so that the chopstick comes out the other side of the straw but does not pass the end of the eyepiece. If the chopstick is pushed too far though the straw, past the end of the eyepiece it will come very close to your other eye when you look through the stroboscope. Given this, it makes sense to look through the scope a few times before you glue the disk in place to make sure you can use it comfortably. 



When everything is aligned, glue the washer to the disk and glue the disk and washer to the chopstick on the non-straw side to keep friction down. 






Finally, add a tape flag on the back of the chopstick to prevent the chopstick and disk from falling out and you have a finished Stroboscope. To use, point at something moving, close one eye and look through the eyepiece with the other while spinning the disk via the chopstick.  We found twisting the chopstick in front of the disk is the most effective way to get the disk spinning fast, and that trying to spin the shutter disk itself tends not to work well and will eventually break the stroboscopes.



Things to do and Notice:
In the most basic sense a stroboscope is a device that exploits persistence of vision to make moving objects appear slow or stationary. In general our retinas will continue to report light for around a 25th  to a 30th  of a second after the original light source has moved depending on brightness. In the case of the disk stroboscope this plays out in two ways, it allows your mind to see the whole field of the eyepiece not just a slot and it allows this image to persist in the time the shutter is closed. For a project that explains the first effect well, see: http://www.exploratorium.edu/snacks/persistence_of_vision/index.html 
This process also allows what happened over a short time to be perceived over a slightly longer one.  In general the more slots you have and the narrower the slots the better your scope will be at making fast moving objects appear to slow, though the image may appear dim. Conversely, if you use one wider slot, slow moving objects will appear to move in steps, they will appear brighter and will persist somewhat longer. We would suggest looking at things like people playing sports with a one slot disk and things spinning or reciprocating fairly slowly like a record player or a sewing machine.  With two or four slots faster moving things like scroll saws, drills, bike and car wheels and even fans can be made to appear to stop.          

It is possible to use this idea backwards and create a mechanical strobe light simply by shinning a strong flashlight though you stroboscope in a darkened room.  
You can also take stroboscopic photography with a digital camera capable of very slow shutter speeds and through a disk stroboscope that is capable of maintaining a very constant speed (motor driven) see:   http://makeprojects.com/Project/Stroboscope/313/1     


Note: While unlikely looking though shutter disk stroboscopes can theoretically trigger epileptic seizures, like their flash tube based counter parts (strobe lights), as such similar precautions should be taken. 

Designed by Antonio Papania-Davis 2010

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