So I was lying in bed idling around when I brought my finger very slowly to my nose and I noticed that right before they touch, there are several solid lines that appear between them before they actually touch (parallel to the approaching surfaces.)
I thought it might be have something to do with the translucency of the skin, but then I repeated this with solid objects, and the effect is even more pronounced. Instead of 1 to 3 lines filling the space between the approaching objects, there are up to 5 of them when I use solid objects at the same distance or a bit further away than my nose.
I repeated this but with the objects far away from each other, depthwise, and do not get the solid line in between them. But I noticed a different phenomenon: when the objects approach each other, they tend to “bleed” into each other, i.e. when they get “close” enough to each other in my field of vision, the space on the two objects that are “closest” to each other will appear to jump toward each other and fill the space between them.
I think the explanation for this second phenomenon might have to do with the translucency of the skin because the effect is much more apparent when using my fingers than other objects. Furthermore, my fingers appear to have a “fringe” to them that other objects do not, even when they are not next to anything, if I look at them at a distance of about 6 inches: this supports the case that the “bleed” the objects have into each has to do with an area where the total “thickness” of skin the light is going through is enough to stop the light when combined between the two fingers, even in an area we would not normally see as part of a finger if we looked at them separately.
Or I could just be seeing things
So does anyone know anything about these diffraction-like lines or the “bleed” that mostly flesh-like objects have when approached closely together?
Just remember you’re a living organism on this planet, and you’re very safe. You’ve just taken a heavy drug. Relax, stay inside and listen to some music, Okay? Do you have any Allman Brothers?
Ignore the skeptics. I think you are seeing effects of the problem that your eye doesn’t view the world from a point, but rather from a finite disk several millimeters in diameter (the pupil). For one thing, this causes blurring for objects that are too close to focus on. For another, you might be seeing how the different parts of this finite disk actually work a bit differently because your cornea isn’t perfect - everybody is at least a little lumpy.
One experiment would be to put a pinhole in foil, and hole that as close as possible to your eye. Maybe fold it around your eyeglasses if you have any, or maybe tape it to your face (avoid the abovementioned skeptics for this test). What you see should now be darker, but the effects you mention should be much weaker if this is what is going on.
The pinhole effect can be pretty striking (eclipses here and here), and when you combine that with our inability to focus up close and flaws within our lens system, you can get all sorts of strange artifacts. You might even be seeing Airy disk artifacts.
Definitely push the pin through the foil before you put it in front of your eye.
No… wait… I do actually have something to contribute:
There’s an effect (I forget what it’s called) where the fringes of two shadows approaching each other appear to reach out and stick together - I believe this (or something equivalent to it) could be happening here - two blurred objects overlapping in the blurred portion, appearing more solid than before because they add together optically.
Damn, Mangetout, where were you a few years ago? Your method is MUCH nicer.
Jackdavinci, what does “simply a matter of focus” mean? Poor focus has to take some specific form, right? I mean, if you were trying to see sharply, being too close is simply a matter of focus, but if you want to figure out how certain appearances arise, there have to be good detailed mechanistic statements that would have predicted what the OP describes, right?
I know exactly what the OP means and always figured it was diffraction.
You can do it now. The SDMB’s white background is good for this.
Close one eye (so you don’t get any double vision effects from having both eyes open.
Focus on the screen from maybe 12-18 inches away.
Now put your hands together,as if to do the “here’s the church, here’s the steeple” thing, with your forefingers coming together into a triangle (it makes the point of contact bigger then doing it tip-to-tip, so the effect is easier to see).
Bring your hands up to three or four inches in front of your eyes, and slowly move your fingers apart so they are barely touching, and focus through the gap.
If you have your fingers just touching, but without squeezing the pads of them together, you should be able to see the fine fringes or lines that the OP mentions. They look just like diffraction lines so I always assumed that is exactly what they are.
Experiment with focusing and moving your fingers for the best effect. Trying it now I get the best result when my fingers aren’t quite touching each other but are just barely overlapping from the point of view of my eye. Also I am getting funny looks from my work colleagues.
Here’s a previous thread on the shadow penumbra effect I mentioned above (interestingly, I had posted in that thread about objects close to the eye creating a similar effect.
Colophon, I can only see what you’re describing if I hold my fingers so close that I can’t focus on them, or if I purposefully don’t focus on them. It just seems to be an artifact of poor focus. If it was diffraction, shouldn’t I be able to see it with my fingers in perfect focus?
