Is this a diffraction pattern?

[curious2021]

 

[Motore]

https://en.wikipedia.org/wiki/Moiré_pattern

 

[sophiecentaur]

Diffraction patterns and Moiré patterns have a lot in common and it can be difficult to distinguish between them. @Motore has assumed that the patterns are Moiré and they may well be (so not optical diffraction) but there are colours around those fringes, which implies there's some wavelength dependence. You will probably see some of that patterning in diffuse lighting (which doesn't support visible diffraction fringing well. There may be 'beats' between the thread spacing and the regular variation of colours along the threads themselves.
I suggest it's a bit of both because some of the fringes have coloured edges. But also there is clear colouration in the irregularities elsewhere in the picture.
If you want to see diffraction patterns through fabric then look at distant street lights (pinpoints of light) and you can get all sorts of repeated dot patterns. See this link for some pretty patterns, including curtain diffraction.

 

[curious2021]

Diffraction patterns and Moiré patterns have a lot in common and it can be difficult to distinguish between them. @Motore has assumed that the patterns are Moiré and they may well be (so not optical diffraction) but there are colours around those fringes, which implies there's some wavelength dependence. You will probably see some of that patterning in diffuse lighting (which doesn't support visible diffraction fringing well. There may be 'beats' between the thread spacing and the regular variation of colours along the threads themselves.
I suggest it's a bit of both because some of the fringes have coloured edges. But also there is clear colouration in the irregularities elsewhere in the picture.
If you want to see diffraction patterns through fabric then look at distant street lights (pinpoints of light) and you can get all sorts of repeated dot patterns. See this link for some pretty patterns, including curtain diffraction.

Thanks for the reply. I’m confused though. My reading of the Moire pattern is that it’s caused by two overlapping patterns which produce multiple slits that the light passes through, diffracts and interferes, producing an interference pattern? So Moire patterns are really interference patterns? From what you’ve said though, it sounds like I’ve read that article wrong?

great spot on the color too. I never noticed it, but can see it plainly now.

 

[hutchphd]

Moire patterns are not diffraction related. They are simply the effect of slightly different periodicities of screening adding together. I like to think of them as the same physics as a Vernier scale. They are " interference" patterns but not in the usual physics meaning related to waves and diffraction.

 

[sophiecentaur]

So Moire patterns are really interference patterns?

They are the result of the interaction of two patterns which, with a different hat on, is the same as optical interference where two wave patterns add together in different ways in different places. I guess you could say that there is interference in both cases but diffraction only in the optical case.
This is yet another example where classification and terminology can trip us up if we don't look deeper at the details. School level learning has a lot of this and a lot of teachers still have the same attitude as their forebears stressed the importance of Kings and Queens of England and the rote learning of 'Capes and Bays'.

great spot on the color too.

Hah - I spotted it but not sure if I can actually explain it!
Edit: perhaps it's refraction / dispersion in the fibres (like raindrops and rainbows).

 

[Orthoceras]

On the photo of the curtain, the red fringes and the green fringes seem to have identical intervals. That suggests the color fringes are not due to diffraction, but due to 'color moiré'. Color moiré is essentially the same as brightness moiré. Color moiré occurs if the red, green and blue pixels are located next to each other on the sensor, for example by the use of a Bayer filter. In low resolution cameras, the color moire effect was reduced by using a blur filter in front of the sensor. In high resolution cameras the color moire effect is less conspicuous, and no blur filter is needed.

 

[sophiecentaur]

In high resolution cameras the color moire effect is less conspicuous, and no blur filter is needed.

[Edit: important to know I'm talking about my Pentax SDSLR]. There is no blur filter (Anti-aliasing) but, if you are taking critical pictures where the moiré is noticeable, the sensor is vibrated (same motors used as for dust elimination and star tracking). Cool eh?

 

[Motore]

My reading of the Moire pattern is that it’s caused by two overlapping patterns

I think in this case that one pattern is the curtains (mesh with the threds) and the other is the camera sensor. (I see @Orthoceras beat me to it)

https://photographylife.com/what-is-moire

 

[sophiecentaur]

I think in this case that one pattern is the curtains (mesh with the threds) and the other is the camera sensor. (I see @Orthoceras beat me to it)

https://photographylife.com/what-is-moire

It looks to me like the lines of threads and the pattern on the threads themselves. This can be resolved if the OP saw the patterns before he took the picture.

 

[curious2021]

I think it’s maybe both.
I saw the patterns with the naked eye, so that’s presumably Moire with two layers of curtain material interfering.
The color fringes I think only showed up in the image, so that could be inteference with the sensor. I’ll check the next time the sun shines through there again.

Thanks a mill for all the explanations btw. I think I get it now. Nice to finally understand!