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Author Topic: Mysterious optical effect of spiral on stem  (Read 1200 times)

ta0

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Mysterious optical effect of spiral on stem
« on: May 05, 2024, 09:53:15 PM »

Playing with the koma that ejects the dragon, I noticed something that surprised me. Although the red line on the stem is a spiral going around it, while spinning I see static rings (a little fuzzy, but well located). That's not what I would have expected. The spiral should slide up (or down) when the stem rotates, fusing into a single color with the background if spinning fast. I then tried with a chasing koma (okkake koma) that also has a red spiral over the stem and had the same effect (what I had seen but not paid attention to until now).

Unfortunately, I cannot show the effect with a video, as the frame rate will cause a stroboscopic effect. Here is a photo of the tops (that I spun by themselves):



No, it's not due to a strobe effect of the lights: it works the same under sunlight.

When I attached the okkake koma to a drill, the effect was not present. Instead, I saw what I expected: a moving spiral a low speeds that at high speeds becomes just a uniform pink.
I guess the effect must be produced by a combination of the spin plus the wobbling of the top. But I need to further think about it.

I would be curious if somebody can also see this effect. You just need a top with a long stem and paint a spiral around it.
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Iacopo

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Re: Mysterious optical effect of spiral on stem
« Reply #1 on: May 06, 2024, 11:49:07 AM »

When I attached the okkake koma to a drill, the effect was not present. Instead, I saw what I expected: a moving spiral a low speeds that at high speeds becomes just a uniform pink.
I guess the effect must be produced by a combination of the spin plus the wobbling of the top. But I need to further think about it.

I think you are right, the wobble could be responsible for the effect.
I have an idea about it:
I suppose that the wobble is due to unbalance, so that the wobble is synchronized with the spin speed;
If the top spins clockwise, when the stem is moving towards the left, because of the wobble, the figure painted on the stem, (the spiral), will appear to move towards the left faster, because of the combined movements of the spin and of the wobble.
But when the stem moves towards the right instead, because of the wobble, this will make the figure painted on the stem to appear to move slower.
Since the wobble is synchronized with the spin, the side of the stem appearing to move faster is always the same; when the movement appears faster, the white areas of the spiral appear darker, at those heights, and this produces the static rings.
I think that a photo with a long enough exposure, (2 seconds ?), could reproduce the effect.     
 
« Last Edit: May 06, 2024, 11:55:46 AM by Iacopo »
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ortwin

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Re: Mysterious optical effect of spiral on stem
« Reply #2 on: May 06, 2024, 02:09:22 PM »

Very good ideas Iacopo!
Now please turn that into a balancing method some way. Maybe by putting a ring on the stem that changes colors like a rainbow?
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ta0

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Re: Mysterious optical effect of spiral on stem
« Reply #3 on: May 06, 2024, 05:50:01 PM »

This is a 1 second shutter photo and, as Iacopo expected, you can see the static lines. But I'm really surprised how defined they are, with the space between them almost the same color of the background wood.

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Iacopo

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Re: Mysterious optical effect of spiral on stem
« Reply #4 on: May 07, 2024, 06:45:30 AM »

Now please turn that into a balancing method some way. Maybe by putting a ring on the stem that changes colors like a rainbow?

Could you explain your idea ?

But I think that your intuition is correct, and some balancing method could be developed starting from these observations.

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ortwin

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Re: Mysterious optical effect of spiral on stem
« Reply #5 on: May 07, 2024, 11:35:15 AM »

Not very well thought through this idea, somehow the main colour you see should tell us something.
Maybe I make a ring half black half white to start with and see what happens.
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Iacopo

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Re: Mysterious optical effect of spiral on stem
« Reply #6 on: May 07, 2024, 01:55:15 PM »


This is the mine, I used some adhesive tape for to make a white spiral on the stem:



When the top spins balanced, (second photo, exposure 10 seconds), some horizontal rings appear on the stem, (they are visible from live too), but I think that this is my fault, the spiral is not accurate enough and the percentage of black and white is not always the same at the various heights. Otherwise the color on the stem should be uniform.

In the other two photos the top is unbalanced and it is wobbling, (the exposure is always 10 seconds); the rings now look tilted and they are very evident. 
 

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ta0

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Re: Mysterious optical effect of spiral on stem
« Reply #7 on: May 07, 2024, 02:37:00 PM »

Very nice photos.

I still find it surprising that it works as well as it does.

I'm guessing that if the spiral was colored into 4 sectors (front, sides, back), you could see perhaps three colors in the slanted rings.
With the wobble precessing, these colors would be slowly shifting.
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Iacopo

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Re: Mysterious optical effect of spiral on stem
« Reply #8 on: May 07, 2024, 03:18:20 PM »

I'm guessing that if the spiral was colored into 4 sectors (front, sides, back), you could see perhaps three colors in the slanted rings.
With the wobble precessing, these colors would be slowly shifting.

I am going to try...
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ta0

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Re: Mysterious optical effect of spiral on stem
« Reply #9 on: May 07, 2024, 05:54:31 PM »

I'm guessing that if the spiral was colored into 4 sectors (front, sides, back), you could see perhaps three colors in the slanted rings.
With the wobble precessing, these colors would be slowly shifting.

I am going to try...

I was hoping you would . . .  ;)

Perhaps just color dots on the spiral would also work.
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ortwin

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Re: Mysterious optical effect of spiral on stem
« Reply #10 on: May 08, 2024, 02:00:00 AM »

...

Perhaps just color dots on the spiral would also work.


Why spiral? What about dots on a ring?
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ta0

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Re: Mysterious optical effect of spiral on stem
« Reply #11 on: May 08, 2024, 10:44:43 AM »

...
Perhaps just color dots on the spiral would also work.

Why spiral? What about dots on a ring?
I think you would get some color mixing with rings. But it's also worth trying. That's your homework  ;)
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ortwin

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Re: Mysterious optical effect of spiral on stem
« Reply #12 on: May 08, 2024, 01:51:22 PM »

...
Perhaps just color dots on the spiral would also work.

Why spiral? What about dots on a ring?
I think you would get some color mixing with rings. But it's also worth trying. That's your homework  ;)
Yes, but homework needs to be done at home. And I am traveling at the moment. So, next week then.
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Iacopo

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Re: Mysterious optical effect of spiral on stem
« Reply #13 on: May 08, 2024, 03:14:21 PM »


This is the unbalance wobble with the spiral painted in four sectors, red, yellow, blue and black.
The red sector of the spiral is in the side with the added weight; that side of the stem is the more tilted outwards so the spiral in the photo appears red at its sides.
The side opposite to the red one is blue; the blue side of the stem spins staying tilted inwards, so in the photo we see the blue only in the central part of the spiral.



This can be used for to detect the heavy side of the top; the color appearing at the sides of the spiral tells the heavy side of the top.

I think that making a ring instead of a spiral as Ortwin suggests would work too, but the spiral is nice.
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ortwin

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Re: Mysterious optical effect of spiral on stem
« Reply #14 on: May 08, 2024, 05:26:04 PM »

Nice!
A theoretical advantage of a ring over the spiral could be, that a ring could easily be repositioned by some angle to maximize the visual effect leading also to higher accuracy of the method.
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