When I printed in the darkroom, I would usually take a piece of cardboard, and use it to block the light in a way that the edges of the print would receive additional exposure. This was called “burning in the edges,” and it would make the edges of the print slightly—almost imperceptibly—darker. Why did I do this? Well, because Ansel told me to. But the real reason is that our eye is drawn toward brighter parts of the print, and darkening the edges slightly keeps the viewer’s eyes from wandering out of the frame.
In Lightroom, the same effect is easy to achieve, and I use it on almost every photograph I publish. It’s “Post-Crop Vignetting” in the “Effects” panel:
Move the “Amount” slider in the negative direction to darken the edges. I usually use −10 to −20, which is a modest effect. The strength of a given setting will also depend on the tone controls of the overall image, like Contrast.
Most of the time, I don’t want my vignetting to be noticeable, but one thing I’ve realized is that it’s more obvious the smaller an image is. So vignetting that might look just right when viewed full-screen looks a little more obvious in a small thumbnail. For images viewed online, we don’t necessarily know what size our audience will view them at, so we just have to make a reasonable guess.
Note—especially for people who aren’t Mom: Most lenses are naturally darker at the edges of the frame, especially at large apertures. The Micro Four-Thirds system, for better or worse, usually corrects this darkening in software automatically. For other systems, you could rely on this natural vignetting to provide darker edges, but if you crop the image off-center, the lens vignetting will also be off-center. So I usually correct the lens vignetting with “Enable Profile Corrections” then add back Post-Crop Vignetting as desired.
I don’t usually adjust any settings besides Amount, but sometimes it’s worth playing around with them. If you temporarily increase Amount, and set Feather to 0, you can better see the effect of Midpoint and Roundness on the shape of the vignette. Try it!
If your primary subject is off-center, you might want the vignetting to be centered (brightest) on the subject. You can achieve this through the Radial Filter, one of the local adjustments:
After choosing the Radial Filter tool, set the Effect to “Burn (Darken)” and drag a circle on your image, from the center of your subject outward. The strength of the effect is controlled by the Exposure slider in the panel, and there’s a Feather adjustment to control how abrupt the effect is.
I have, however, found that the Radial Filter is often more obvious than the regular Post-Crop Vignette. A larger circle, and a larger feather value, can help mitigate this. Like I said above, the effect is often more obvious in a smaller image, so I often look at the thumbnail in the Navigator panel to decide if it’s too obvious.