I just took a photo with manual focus and blurred as much as I could a light, but instead of getting a uniform colour, there are dots, like dust :

enter image description here

Do you know what's causing the darker dots?

  • I take it this is a 1:1 crop from a small portion of the frame? – mattdm Aug 29 '15 at 16:06
  • @mattdm yes, this is a cropped photo (that has by the way also been zoomed with a lens), why ? – Trevör Aug 29 '15 at 16:14
  • Because it's a big difference whether this is a pixel-peeping magnified view or the whole scene. – mattdm Aug 29 '15 at 16:22
  • Other information that would be useful: RAW or JPEG from the camera? If RAW, processed with what software? – mattdm Aug 29 '15 at 16:26

Since you're looking at the pixel level, these artifacts are too small to be dust. It's also unlikely that dust would be outlined sharply when you're using a wide aperture.

I think it's most likely that they are random shot noise combined with demosaicing artifacts, possibly then also smoothed out by denoising.

  • I don't think it's noise since it's always there (and position varies with lens zoom). – Trevör Aug 30 '15 at 4:51
  • Can you post an example of that? – mattdm Aug 30 '15 at 5:23

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