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Author Topic: Spinning Tops and Optical Illusions utilizing persistence  (Read 1822 times)

Neff

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Re: Spinning Tops and Optical Illusions utilizing persistence
« Reply #15 on: July 14, 2016, 12:28:33 AM »

Drew Tetz has been working with this effect a lot lately





can be spun on a record player or as a finger top

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Jeremy McCreary

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Re: Spinning Tops and Optical Illusions utilizing persistence
« Reply #16 on: July 14, 2016, 03:06:50 AM »

Tetz' tops are gorgeous, Neff. Would love to see the last one spinning.

I find that the dynamic patterns created by spinning tops can be very hard to predict from their appearance at rest -- whether in video or in person. One advantage to building tops with LEGO is that it's often easy to tweak the static pattern repeatedly to get just the right dynamic effect.

« Last Edit: July 14, 2016, 04:31:38 AM by Jeremy McCreary »
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the Earl of Whirl

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Re: Spinning Tops and Optical Illusions utilizing persistence
« Reply #17 on: July 14, 2016, 10:37:22 AM »

Drew Tetz always seemed to have a secret love of top spinning.  He was just never quite able to lay his yoyo down long enough to get fully immersed in our sport.  Glad to hear he is still doing some whirling activities!
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Lourens

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Re: Spinning Tops and Optical Illusions utilizing persistence
« Reply #18 on: July 14, 2016, 12:02:20 PM »

Thank all of you very much for your reactions and Neff for showing the work of Drew Tetz. But most of all, I like the spinning tops!
I have several spinning tops which are worthwhile showing but making videos is not my thing! But maybe in future.
For now i have a photo from the caleidoscopic Colour Top, made by John Gorham (1858). Every disc  (in different sizes, colours) has a small and thin rope on it. If you make the top spinby pulling its own rope, the discs on it get on turning. By touching the rope at the disc while top is spinning tou change the speed of one of the discs and that will change the patterns. Hope to show it in future on a video but for now ... that's all folks!
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Jeremy McCreary

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Re: Spinning Tops and Optical Illusions utilizing persistence
« Reply #19 on: July 14, 2016, 04:47:14 PM »

.... I have several spinning tops which are worthwhile showing but making videos is not my thing! But maybe in future....

Looking forward to the videos, Lourens! I'm by no means a good videographer, but I may be able to save you some frustration by sharing a very recent discovery regarding my smartphone camera.

When I was shooting all my videos with a high-end Canon digital SLR, the video capture of persistence-of-vision effects in my spinning tops seemed impossible -- no matter how conspicuous to my own 2 eyes. Time after time, the persistence effects were either totally absent or swamped by the stroboscopic and wagon-wheel effects associated with the video frame rate. Long-exposure stills seemed to be my only option.

Then I discovered that the camera in my phone has a "pro" mode that actually gives me =much= more control over video capture settings than my fancy SLR does! I have full control of only two of ISO, shutter speed, and exposure compensation (EC), while the camera retains control of the 3rd, but that's enough!

The video below was shot in a low-light setting at a forced 1/20 sec and ISO 160 with automatic EC.



Overall, I'd call it a qualified success WRT capturing the persistence effects (color mixing, virtual surfaces of revolution, etc.) I saw during the shoot. I had to underexpose it a bit to get the camera's cooperation, but the interference from frame rate effects is generally tolerable.

Hope that helps.

PS: Exposure times longer than the frame interval are quite possible in video and are likely behind my success above. For more on the color-mixing tops in the video, see http://www.moc-pages.com/moc.php/421944.
« Last Edit: July 14, 2016, 04:54:44 PM by Jeremy McCreary »
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ta0

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Re: Spinning Tops and Optical Illusions utilizing persistence
« Reply #20 on: July 14, 2016, 11:23:59 PM »

That's a good hint Jeremy about using the slower camera on your phone instead of the better camera.

I guess the best way would be to record at a high frame rate and then average the frames in post production. Unfortunately (for this application) the usual way of decreasing frame rate is by skipping frames (because it leaves the frames sharp). You probably need to get an advanced editing software (or plugin filters) to be able to blend frames. I think I can do it on Adobe premier, but I haven't tried yet.

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ta0

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Re: Spinning Tops and Optical Illusions utilizing persistence
« Reply #21 on: July 14, 2016, 11:50:58 PM »

I love those tops by Drew!  8) I hope he starts selling them.
They use a strobe effect. In the video the strobe is due to the camera frame rate, I believe. But they could also work with the naked eye under artificial lighting (incandescent, some fluorescent or some LED).
« Last Edit: July 16, 2016, 09:43:22 AM by ta0 »
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Lourens

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Re: Spinning Tops and Optical Illusions utilizing persistence
« Reply #22 on: July 16, 2016, 02:01:16 PM »

Hello Jeremy,
Thank you for the advice and the video of the Lego-tops. Maybe I will try in near future!
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