Equipment is Canon EOS 5D3 (5760x3840) with a 24-105 f/4 L lens at 105mm, ISO 200.
The following are crops from the same small (676x449) section of a couple of blue sky shots I did to test for sensor dirt. The first image is unmodified other than Raw->JPEG conversion in Lightroom with no setting changes, and shows some faint dark circles.
To enhance the circles I cranked up contrast and clarity to 100%, giving this:
However, the same area of an image taken 1 second earlier at f/7.1 shows no evidence of these spots, even after cranking up the contrast/clarity to 100%.
- The spots seem to be more prevalent towards the edges of the original (full-size) image, although there is one spot near the center. None of the spots are visible at f/7.1.
- All the spots appear to be the same size, but have different densities.
Given all this evidence can I deduce that these are lens defects (or dirt on a lens element)?
Since they're completely undetectable at "normal" apertures I don't consider this a problem. I just would like to know what I'm seeing.
BTW, the obvious test is to shoot the same image with a different lens and compare, but I won't be able to do that for several days and thought this might be an interesting question for photo.se.