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I caught a weird effect on camera. Which one?


Vitor Delduque

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9 hours ago, Karim D. Ghantous said:

It looks like diffraction except it isn't. I don't have any idea.

1 hour ago, Phil Rhodes said:

You're not shooting through strange bits of glass, filters, etc? Looks optical to me.

Yeah! It does looks like optical stuff. But I wasn't using or shooting through glass, filters, etc. I was testing a Cine Rokinon 50mm at T1.5, somewhere around 30cm (1ft) from the object. Despite this, the lens looks as it should.

7 hours ago, Mark Kenfield said:

I'd have pegged it for a LongGOP encoding artifact of some kind? What format did you record in?

 

Good one! I'm gonna try to get the effect again and if I do, I'll try All Intra next.

 

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4 hours ago, Vitor Delduque said:

LongGOP doesn't seem to be the problem. Here's the All Intra test.

On the other hand, it seems that the effect follows the background, specially the white chair and brighter objects. Back to diffraction? 

OBS: shutter speed, distance and fps don't change a thing.

Did you try a different lens?

 

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https://physics.stackexchange.com/questions/111006/how-does-light-bend-around-my-finger-tip

Quote

This effect is caused by the background being (slightly) out of focus, and by the foreground object effectively occluding part of the camera/eye aperture, causing the effective aperture (and thus the resulting image) to be shifted.

I've noticed while comparing blue screen composites with real images that a foreground object will distort the background and also make the background appear more in focus than it otherwise is because the foreground is working as an aperture somehow. 

Edit: except it seems to be the foreground that is acting strange for you? Try it at other apertures. I think it's optical but am not sure. 

Edited by M Joel W
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2 hours ago, Uli Meyer said:

Did you try a different lens?

 

Yup. Same effect with the 35mm, but I noticed something about the next quote

1 hour ago, M Joel W said:

https://physics.stackexchange.com/questions/111006/how-does-light-bend-around-my-finger-tip

I've noticed while comparing blue screen composites with real images that a foreground object will distort the background and also make the background appear more in focus than it otherwise is because the foreground is working as an aperture somehow. 

Edit: except it seems to be the foreground that is acting strange for you? Try it at other apertures. I think it's optical but am not sure. 

When I tested with the 35mm I started at the same distance I was with the 50mm (T1.5 also) cause I wanted to maintain the same "size relationship between foreground and background" (sorry.. what do we call this in english ??). The effect was almost imperceptible. So I tried again a little closer to the candle and the effect was back.. I think it was due to the DoF beeing closer to the one I had with the 50mm. This should add some credit to the article. I think that's it.

Thanks very much for all the answers ? Feel free to add any ideas!

Edited by Vitor Delduque
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