What causes this diffration pattern?

[Tuolumne]

The attached photo was taken with a Ricoh Caplio GX-100 at 25mm. There are two large, clear diffraction patterns in the photo: one near center and the other at the center left. At first I thought these might be caused by some sort of reflection of the flash off dust particles rising from the BBQ grill. But I don't think so. I have seen these diffration patterns on other shots @25mm taken with the flash indoors. Anyone have any idea what causes this?

/T

 

[oftheherd]

Reminds me of what you would get with snowflakes and flash. I would guess that you had something, perhaps particles from the charcoal that, were large enough to return an out of focus reflection.

 

[keithwms]

Looks like perhaps there was moisture on your lens or sensor. Is that possible? Other than that I think I see a lot of high ISO noise.

 

[Tuolumne]

Looks like perhaps there was moisture on your lens or sensor. Is that possible? Other than that I think I see a lot of high ISO noise.

It was shot at ISO 1600. I forgot to turn the speed down when I went from available darkness to flash.

/T

 

[planetjoe]

I'd agree with the "snowflake" theory, but I would also add that the object would need to be relatively close to the lens, if not on it. For example, check out this website, which in all honesty is a random Google result. Scroll down to the heading "Flashlight and ghosts".

The gist of the idea is pretty obvious: the particles close to the lens get an exponentially higher illumination than distant objects, and tends to produce this result.


Cheers,
--joe.

 

[Bryce]

It is largish particles in the air very close to the lens, like an inch or two (and the flash) but not on it. Were it on the lens it couldn't very well be illuminated by the flash, right?
This problem is especially serious with small sensor camera and ones with the flash near the lens. Were the sensor larger, the OOF particles would be so blurred you wouldn't see them; were the flash further from the lens, the particles wouldn't be so brightly lit.

 

[planetjoe]

This, of course, is an excellent point.

I think I was in-between two different crackpot explanations, but I was preoccupied with the idea of "diffraction"; classically speaking, I was trying to imagine some mechanism by which light from behind the speck diffracts around it.

The more probable mode, of course, is exactly as you say - corroborated, in fact, by the "literature" - the diffraction pattern (if indeed it really is one; we're presupposing only be appearances, I think) is produced in the camera's optical path, rather than by the source particle itself. In this more likely mode, the source particle behaves as a point source of intense illumination.

Were it on the lens it couldn't very well be illuminated by the flash, right?

Cheers,
--joe.

 

[Tuolumne]

This, of course, is an excellent point.

I think I was in-between two different crackpot explanations, but I was preoccupied with the idea of "diffraction"; classically speaking, I was trying to imagine some mechanism by which light from behind the speck diffracts around it.

The more probable mode, of course, is exactly as you say - corroborated, in fact, by the "literature" - the diffraction pattern (if indeed it really is one; we're presupposing only be appearances, I think) is produced in the camera's optical path, rather than by the source particle itself. In this more likely mode, the source particle behaves as a point source of intense illumination.




Cheers,
--joe.

It is hard to tell in this small size image, but the full size image clearly shows a true diffraction pattern. The one at the center of the image is quite nicely formed with evenly spaced circular rings around a point source. The circle to the left center shows a fair amount of what looks like coma and the diffration circles are quite fuzzy and not at all sharp.

/T

 

[Tuolumne]

BTW, attached is another image taken indoors, Ricoh Caplio GX-100 @25mm, with flash, that shows an enlargement of another diffraction circle that appeared in the photo. No smoke particles around at all this time.

/T

 

[Bryce]

See if you can't reproduce it by firing the camera with flash and focused at least several feet away while some tiny object is held just in front of the lens.
I don't have a good explanation for the diffraction like pattern but I'm sure you'll be able to reproduce the image as I've laid out.
I'm pretty sure because I've seen this repeatedly from friends' compact digital cameras, and usually in conditions where there is a lot of stuff floating around in the air. Of course there is always some, that is why you have to dust your house!

 

[Chris101]

I heard they are called 'orbs' and they are dead people's personalities, or beings from another dimension or maybe the exhaust from tiny spaceships. Something like that. Congratulations Tuolumme, I've been trying to capture these for a while now, and all I get are blurry pictures!

(woooo oooooooo.....)

 

[Abbazz]

There are two large, clear diffraction patterns in the photo: one near center and the other at the center left. At first I thought these might be caused by some sort of reflection of the flash off dust particles rising from the BBQ grill. But I don't think so. I have seen these diffration patterns on other shots @25mm taken with the flash indoors. Anyone have any idea what causes this?

There seem to be two different issues. First, the big reflection in the center of the frame is the back of your lens illuminated by the light coming from your subject, which is reflected back by the sensor. See these samples: http://www.pbase.com/pganzel/ccd_lens_flare_testing

Apart from the center reflection, the second issue seems to be some smoke particle in front of the lens reflecting the bright light from the flash. As stated by others, it happens frequently when there is snow, dust or mist illuminated by the flash right in front of the lens.

Cheers!

Abbazz