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I took a series of photographs just before sunset, directly into what was a very weak, watery sun - barely made you squint to look at either with the naked eye or through the viewfinder.

To the naked eye, the sun had a light halo surrounding it, diffusion by the atmosphere - which later turned out to be sand & dust being brought over by Hurricane Ophelia.

However, on the exposure, that halo became darker than the surrounding sky rather than lighter.

I'm aware the sun itself is completely blown out, & though overall I think it gives the picture an interesting look I'd just be interested in knowing how it happened.

enter image description here

No post-processing at all, other than defaults applied by NikonView & conversion to jpg for upload here.
D5500 18-300mm f3.5-6.3G - 300mm ISO 100 1/1600 f6.3

I tested other apertures/speeds, but all show the same effect to greater or lesser degree, not related to the aperture itself.

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    \$\begingroup\$ Was Active D-Lighting on for this picture? \$\endgroup\$
    – scottbb ♦
    Commented Oct 18, 2017 at 11:39
  • \$\begingroup\$ Ahh, it was, on Auto - though D-Lighting HS [& everything else] is at zero in ViewNX. \$\endgroup\$
    – Tetsujin
    Commented Oct 18, 2017 at 12:20

3 Answers 3

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This can happen when there are strong light light sources in the scene (such as shooting sunrises/sunsets like yours), when Nikon's Active D-Lighting is on. Active D-Lighting (ADL) tries to help balance an image that has areas of high local dynamic range; essentially, it is a form of high dynamic range processing.

ADL slightly reduces the exposure, so darker regions near high dynamic range transitions can be boosted. There is also some tone curve adjustments that occur. Importantly, ADL is applied before/during the exposure. It is part of the image.

Caveat: CaptureNX2 can remove ADL if it was set to "Low". But any other setting, or any other processing tool (such as ViewNX2) cannot completely remove the effects of ADL.

Note that D-Lighting is not the same as ADL. D-Lighting is applied in the Retouch menu in camera, and if shooting RAW, can be removed/disabled by CaptureNX2 and ViewNX2 even if was applied in the camera's Retouch menu.

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  • \$\begingroup\$ Confirmed. Thank you. This is now off in the camera:/ Separate answer put in just to show a picture of the result. \$\endgroup\$
    – Tetsujin
    Commented Oct 18, 2017 at 15:03
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Separate answer, just to show confirmation of scotbb's diagnosis.

CaptureNX-D with Active D-Lighting overridden.
Screen shrunk just to show relevant info.

enter image description here

As to whether or not it's an optical illusion, here is a crop of the image, with [L] & without [R] Active D-Lighting, no other changes.

enter image description here

Further example of composite image...

enter image description here

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There is no halo - it's an effect that your brain generates. If you cover the sun with your fingers or a dark piece of paper, the 'halo' is gone.

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    \$\begingroup\$ if it's entirely an optical illusion, how come you can switch it off? Side by side comparison added to my answer. \$\endgroup\$
    – Tetsujin
    Commented Oct 18, 2017 at 16:49
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    \$\begingroup\$ The effect is well known and measured, so the software knows how much to brighten the image where, to make it look perfectly smooth to our brain. \$\endgroup\$
    – Aganju
    Commented Oct 18, 2017 at 16:54
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    \$\begingroup\$ Did you hover a colour-picker over both versions? I did. \$\endgroup\$
    – Tetsujin
    Commented Oct 18, 2017 at 16:57
  • \$\begingroup\$ @Tetsujin Did you mask the sun's disk and look at the "halo" without the brighter part of the image visible to your eyes? The halo is there, but it is nowhere near as pronounced as you perceive when the sun is visible. \$\endgroup\$
    – Michael C
    Commented Oct 19, 2017 at 8:52
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    \$\begingroup\$ I did & I saw an apparent change - but the eye-dropper doesn't lie; the colour actually changes in the halo compared to outside it. If it was entirely optical illusion, then both versions of the image would demonstrate the halo to some degree. That could actually imply that the act of covering the bright spot is more an illusion than not covering it. \$\endgroup\$
    – Tetsujin
    Commented Oct 19, 2017 at 9:00

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