Recently I was doing some night sky photos using my D850 and the Nikon 20mm f/1.8. When I looked at the shots in Lightroom I noticed something odd: in the darker areas, especially toward the corners of the frame, a series of faint concentric rings were visible, apparently emanating from the center of the image. I did not have any sort of filter on the lens, so this could not be some sort of interference pattern. What was happening?
I started doing a lot of testing. I finally discovered that these “rings” would disappear if I unchecked the “lens profile correction” in the Lens Corrections tab in Lightroom’s Develop module.
Was this a bad lens profile or what? I considered some options:
- I first noticed this while working on my laptop which has a high resolution 4K screen. Was this just a monitor artifact? I opened the same files on my desktop computer which has a much larger, but slightly lower res monitor. Nope, the circles were still there when “lens correction profile” was on.
- Was this only a factor of high ISO in dim light? I needed some control shots, done in dim light. With my camera firmly mounted on a tripod I snapped a series of images inside my garage with the garage door closed and the overhead lights turned off. I kept the lens at f/2 and went from ISO 100 to ISO 12800 in one stop intervals, with shutter speeds from 30 seconds up to 1/4 second. The rings were still visible in all the images when I turned on the “correction profile.”
- What about shooting in more “normal” lighting conditions? I went outside and shot a series looking down my street, at different exposure values and different ISOs. I could not see any problem in the images when the profile was on or off.
- What about aperture settings in dim light? Back to the garage and another series of frames, this time done at ISO 6400 and apertures from f/2 to f/11. No change, turn the profile on and the rings were still there in all the shots.
- What this a problem with the 20mm? What about other wide angle lenses? More shots in the garage, this time with my Nikon 14-24mm. As soon as the lens profile was applied in Lightroom I could see the rings, although fainter. I also tested the only other wide angle lens I own, the Nikon 16-35mm, and the rings were back. Again, if I unchecked “lens profile correction” the rings disappeared.
- What about the lack of an anti-aliasing filter on a high-res body? I no longer own a D800E or a D810. I didn’t own the 20mm f/1.8 back when I had those cameras, but I did have night sky shots taken with the 14-24mm. I pulled those up, looked at them carefully, and flipped the profile correction on and off. No rings no matter if the correction was on or off.
What on earth was going on here? Was this a problem specific to the D850?
Now totally frustrated, I looked at my Develop settings in Lightroom. If sure would be great to be able to use those lens profile corrections to solve the distortion and vignetting problems that all wide angle lenses have. I discovered that if I set the sharpening Amount slider to zero the rings disappeared, but in my normal RAW file workflow I generally do want to apply some sharpening. Back at the Lens Profile tab, I left the “profile correction” on, but pulled the sliders for Distortion and Vignetting at the bottom of that tab to zero, effectively negating the profile. Sure enough, the rings disappeared. But wait…how about separating those two sliders, adjusting one but not the other? The culprit seemed to be the Distortion slider. I could have the Vignetting slider all the way to the right, as high as possible, but the moment I moved the Distortion slider from the zero position the rings started to show.
As I stated earlier, I’ve only seen this in very low light shots, and haven’t tried any tests with longer focal lengths. Has anyone else shooting with a D850 seen similar results? Right now I’m thinking that when I’m processing images taken with the D850 in very low light I will leave lens profile correction turned on, but pull that Distortion slider to the far left before slowly moving it to the right.
On the theoretical side, I’m surprised it was the distortion that causing this effect. Vignetting would have been my guess as changes to ‘exposure’ in the corners might result in combing.
On the practical side, unless your distortion for this lens in high, and there are prominent horizontal or vertical lines in the image, it likely does not matter if it’s ‘on’.