How do you take a photograph through a mesh

August 2, 2008 10:35 AM

At night, through the mesh netting of my tent, I often observe a beautiful effect that forms around the moon - sort of "shockwaves" or lines that spread out from it in four directions. It's some sort of diffraction illusion? How do I photograph it?

Here's my best attempt - so fuzzy / out of focus you may not be able to tell what I'm talking about. It looks really amazing though, anyone know what I'm talking about and know how to explain the science behind it? Thanks!

http://www.wavejumper.org/MoonDifraction.jpg

posted by wavejumper to sports, hobbies, & recreation (10 comments total)

Moire?
posted by box at 10:42 AM on August 2, 2008

You're halfway there with the name of your file.

The screen is acting as a Diffraction Grating, and and example of this phenomenon can be had here.

I think to better photograph it, you'll need to manually focus on the target, not the screen.
posted by tomierna at 10:42 AM on August 2, 2008

I think this is an example of a Moiré pattern. This might be difficult to capture accurately, because it's technically an artifact itself. Slow shutter speed and low compression on a decent camera? Try different things.
posted by disillusioned at 10:42 AM on August 2, 2008

Here's another one from the movie "Atonement." How did they photograph that?

http://www.wavejumper.org/screenshot_01.jpg
posted by wavejumper at 11:00 AM on August 2, 2008

it's not a moire pattern; it looks like diffraction.

a moire pattern would need two meshes (the pattern comes from when the two overlap or not) and would be present whether the moon was there or not (ie during the day too).

the evidence from diffraction is that the extensions are along the two principal directions of the mesh grid (which wouldn't be the case for moire).

however, the spacing of the lines in the grid/netting is completely wrong for diffraction - way too big. my best guess is that it's diffaction from the gaps between the fibres within the threads that make up the netting. is the netting made from threads that have many separate fibres? if not, my idea makes no sense.

as tomerina said, you want to focus on the moon (ie "at infinity") rather than on the netting for the best photo.

lucky you for seeing something so neat...
posted by not sure this is a good idea at 11:06 AM on August 2, 2008

that photo from atonement would be taken with a filter on the camera that includes a diffraction grid.
posted by not sure this is a good idea at 11:07 AM on August 2, 2008

however, the spacing of the lines in the grid/netting is completely wrong for diffraction - way too big.

no - the threads are effectively the slits, not the mesh spacing. remember babinet's principle? you can replace the netting with its inverse and get the same diffraction pattern.
posted by sergeant sandwich at 11:25 AM on August 2, 2008

ah, that makes sense. thanks.
posted by not sure this is a good idea at 11:39 AM on August 2, 2008

There are special filters you can get for your camera to produce these and other effects. I'd eliminate the mesh from your tent and find something designed for the purpose.
posted by ikkyu2 at 12:05 PM on August 2, 2008

When! The!
Lines that you're seein'
Make more lines in between
That's a moire! (That's a moire!)

Now you won't forget.

I'm sorry if you wind up singing that all day.
posted by cmyk at 4:20 PM on August 2, 2008 [1 favorite]