An intentional lens flaw.
I've had Adobe Lightroom installed on my iMac for the past two years . Since I never really had the urge to get back into digital photography, it pretty much sat there with the occasional one off quick photo touchups that I didn't want to do in Photoshop. I had bought a book before on how to use it, breezed through it, but never really applied what I learned. That mindset has totally changed now.
Since getting bit by the photography bug again after my purchase of a Speedlite Flash — something I have been missing from my equipment for sometime, I have been using Lightroom non-stop to enhance and change the photos I take. Granted, setting the correct ISO, aperture, and shutter speed should give me the best exposure every time, I find that my art side comes out when I manipulate the photos beyond what the camera initially gives me.
One feature that I have fallen in love with using in Lightroom is a photographer's nightmare when it comes to their lenses. I am talking about lens vignetting. Vignette happens in a lens when light falls more on the center of the image and less so on the outer edges. This creates a more underexposed look to the corners of the frame.
Lightroom allows you to change the vignette of the image you are developing, either in the positive (lighter corners) or negative (darker corners) direction. It's more for use to help correct images if this occurs in the photograph, but I like to intentionally add a negative vignette to some of my photos. This purposely adds the dark rim around the edge of the photo.
The reason I do this is because I feel that it brings the eye into to the photo. It also tends to add a sense of dramatics to the scene that otherwise would not be there. Now, like I mentioned, some photographers would hate to have their lens do this to their photograph, luckily my Canon lenses do not do this, I just choose to give the impression that they do. I also find that adding a higher saturation of color — if my final product is to be color, adds an even more range of emotion to the photograph.