This has very little to do with photography, but given the light/colour nature of the question I'm expecting that those who understand the "physics" behind photography/light/colour will also be able to answer this question...
I was sat in an evening lecture the other week - the lights were dimmed and there was a powerpoint presentation being projected onto a white screen. The slides were mostly black and white (text and/or x-ray images). I was sat behind someone (a large table's diameter away) and could see the whole screen apart from where this guy's head was. When I moved my eyes from side to side or blinked rapidly (as I got bored with the topic) red, green and blue vertical lines would appear over the silhouette of this guy's head (nowhere else, just over the area where the guy's head was overlapping the screen).
It got me intrigued... Can anyone offer an explanation of how/why this happens?! Thanks!!
@lluniau Funny you say that... Holly Anna's (@redwax66) pic of the moon this week had similar 'aura' - made me wonder why. Thought it must be something to do with the spectrum being broken up?
@lestat@binny Possibly - but I was thinking it was something other than "something in my eyes/head"! Something more technical maybe. If I had known anyone else there I would have asked them if they could see it too.
@filsie65 Yup - I think I see what you mean. And although it's not the same, it's a similar sort of thing.
@mallocarray Now that sounds more like what I was expecting! It's all a bit too complex for my complete understanding (!) but this paragraph makes me think it's probably what I was describing -
"This effect is caused by the way the eye follows a moving object on the projection. When an object on the screen moves, the eye will follow the object with a constant motion, but the projector will display each alternating color of the frame at the same location, for the duration of the whole frame. So, while the eye is moving, it will see a frame of a specific color (red for example). Then, when the next color is displayed (green for example), although it gets displayed at the same location overlapping the previous color, the eye will have moved toward the object's next frame target. Thus, the eye will see that specific frame color slightly shifted. Then, the third color gets displayed (blue for example), and the eye will see that frame's color slightly shifted again. This effect is not perceived only for the moving object, but the whole picture."
@filsie65 The moon picture looks to be chromatic aberration, which is due to the camera lens not focusing all wavelengths of light exactly the same. This is visible especially near sharp high-contrast edges.
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Here's wikipedia explanation http://en.wikipedia.org/wiki/Entoptic_phenomenon
@filsie65 Yup - I think I see what you mean. And although it's not the same, it's a similar sort of thing.
@mallocarray Now that sounds more like what I was expecting! It's all a bit too complex for my complete understanding (!) but this paragraph makes me think it's probably what I was describing -
"This effect is caused by the way the eye follows a moving object on the projection. When an object on the screen moves, the eye will follow the object with a constant motion, but the projector will display each alternating color of the frame at the same location, for the duration of the whole frame. So, while the eye is moving, it will see a frame of a specific color (red for example). Then, when the next color is displayed (green for example), although it gets displayed at the same location overlapping the previous color, the eye will have moved toward the object's next frame target. Thus, the eye will see that specific frame color slightly shifted. Then, the third color gets displayed (blue for example), and the eye will see that frame's color slightly shifted again. This effect is not perceived only for the moving object, but the whole picture."
Thanks. I'm happy now :)
@redwax66 - did you know you had posted a chromatic aberration? I think that sounds really cool!