We know that a window can actually reflect light. But if the window has some dirt sticking to it, the image we see sometimes get magnified. Why?

Question

Well, I was traveling in a bus yesterday and saw this occur. The board that separates the passengers from the driver's had something written on it and I saw that the window that was a few meters away from the board reflected all of the things written.. But the window had some dirt on the part where I saw the image of the writings... And, they appeared to be enlarged just at the point where dirt was present.

Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. — Community, Dec 22 '22 at 19:02
Possibly a duplicate of How does light bend around my finger tip? — benrg, Mar 14 '23 at 18:57

score 0 · Accepted Answer · answered Dec 22 '22 at 18:37

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The open spaces between dirt particles each acts like a "pinhole camera" to magnify the image behind the dirty glass pane. The magnification is slight but noticeable. Try this experiment: make a small triangular hole shape by putting three fingertips together so as to leave a gap at their intersection. by pressing your fingertips together, you can make the size of the hole shrink; by relaxing them, you can make the hole larger.

That hole will act as a pinhole camera. now look through the hole at your computer screen from about 24 inches away and vary the hole size. you will find a certain diameter at which the image you see through the hole will get sharper and the text on the screen will become easier to read.

answered Dec 22 '22 at 18:37

niels nielsen

92,630

You may be correct, but I'm skeptical. When I think of a dirty window, I think of a lot of scatterers, not a lot of holes. The situation seems to be reflection not transmission, but I suppose a very small mirror (or element of a glass window) could behave like a pinhole. And if I think of two pinholes, it seems that rays originating at a single point would hit my retina different locations, blurring the image. But ... I may be seriously under-thinking the situation. – garyp Dec 22 '22 at 19:11
One can sometimes observe people looking at a window display though a small gap between two fingers. This produces a sharper image because the entrance pupil of the eye has been reduced and so only a small part of the eye cornea and lens is used to produce an image on the retina. The smaller aperture results in the effect of aberrations in the optical system being reduced and a sharper image being produced on the retina. – Farcher Dec 22 '22 at 21:46

We know that a window can actually reflect light. But if the window has some dirt sticking to it, the image we see sometimes get magnified. Why?

1 Answers1