strange spots on my pictures

[cmazza]

Hi there,

I have finally made the jump to digital and purchased a K10D. I have been playing around with photographing some smoke and found round spots on some of my pictures.

I took the pictures facing a north window. I was using a black sheet as the background but the smoke was back lit by the window light. I was also using a flash as side lighting.

The spots seem to be of varying size and do not appear in the same place in every picture. They also do not appear in every picture. It sort of seems like lens flare but not like any I've seen in film.  I was not using a filter and my aperture only varied between 5.6 and 8.

Any thoughts or ideas would be appreciated.  

I have posted a few pictures here.
http://www.sfu.ca/~cmazza/spots

Thanks
Candida

[PTeeCee]

They do look strange! Perhaps they represent out of focus dust motes that are being lit by the flash (or the ambient light; depending on the relative strengths thereof). I base this on the similarity between the tubular look to what I believe is the out of focus plumes of the smoke and the annular look of the spots. Sort of a "bokeh" effect. The varying sizes is explained by the degree to which the dust motes are in focus. I would like to see an occasional one as a pinpoint dot of specular white light to back up this interpretation. Was there it a dusty backdrop or corner of room etc? Peter

[Jonathan Wienke]

Your link is broken...

[francois]

It was working a few hours ago    Looks like the files were removed.

[cmazza]

Bad timing.  The server where my pictures are stored is down for some or all of the day today for repairs.    .  I forgot.  I am posting one of the pictures with lots of spots.

Peter,

I had another look through the pictures. You could say that the area was a bit "dusty".  I was burning incense which was leaving some particulate in the air.  There was a only a few pictures with pinpoint white spots.  I'm beginning to think that you might be right that it is dust but why would these particles show up as perfect black circles with white rings.  I would have expected more just white spots.  In addition, I would have expected more out of focus spots.  So many are in perfect focus.  Can't say that about a lot of the shots .

I suppose my biggest concern is that this is not a camera issue (sensor, pixel).  I just got the camera and would still be able to exchange it if there is something major wrong with it.

Thanks
Candida

[Peter McLennan]

What happens if you shoot the plain black background?  No flash, no smoke.

[cmazza]

What happens if you shoot the plain black background?  No flash, no smoke.
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Hi Peter,

I took a few shots of a dark background and did not get any round spots or any spots at all.

C.

[32BT]

I suppose my biggest concern is that this is not a camera issue (sensor, pixel).  I just got the camera and would still be able to exchange it if there is something major wrong with it.
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It's definitely not a camera problem. Some of the spots clearly show lens barrel masking which means it is a lens & light issue. It looks like there may be incident light from the side. Perhaps there are particles between the flash and the picture path, but not directly in the picture path. Did you use a lens shade?

[Jonathan Wienke]

I'm going to vote for stray light in the lens as well; a strong light source somewhere out-of-frame hitting the front element and causing flare effects. The spots look similar to the flare spots I get shooting outdoors with my 17-40 with the sun just out-of-frame. Look for open windows, lamps, or shiny reflective surfaces that can shine directly on your lens, and flag them off. It may even be the light source you have illuminating the smoke. Are you backlighting the smoke?

[PTeeCee]

Hi, I agree with another poster that it it does not look like a camera problem (that is the good news!, the bad news is ... if it is not dust, I'm at a loss) the unusual structure may be an example of the so-called "hard" or "wired" or "poor" (sic) bokeh, see www.kenrockwell.com/tech/bokeh.htm. (Fig 1) Sorry I could not get an example at short notice other than that from the redoubtable Mr Rockwell. Peter.