Or keystoning, as it’s more correctly termed, is a factor of photography. When you photograph buildings, keystoning occurs whenever you either point your lens up or down from the horizontal. The result is the lines of the building will appear to converge at the top or, when shooting from a high vantage point at the bottom, of the picture.
This isn’t the effect of lens distortion as many people believe but rather a factor of perspective when capturing a 3 dimensional world on a 2 dimensional medium. The effect may appear more pronounced with wide angled lenses simply because wide angled lenses are more powerful at creating a sense of perspective.
This effect can be avoided by keeping your lens absolutely horizontal, and there are spirit levels you can fit to the flash shoe of your camera to enable this. But, in the case of the cathedral shot below, as I’m not able to levitate to a central point somewhere above the cathedral floor, I had to point my lens upwards to capture the fabulous vaulted ceiling.
Because of this however, the pillars of the cathedral appear to lean inwards, the effect more pronounced at the edges of the picture. There is a however a way to fix this, well two ways, that I know of in Photoshop.
In Photoshop CS5 and earlier, one of the quickest and easiest ways is to use the distort tool to straighten the verticals. If you have Adobe CS6 there is a powerful new tool called the Adaptive Wide Angle filter and I’m grateful to Noeline for pointing me in the right direction and suggesting this as an alternative to the distort method.
In the tutorial below, I show you how to use both methods. This is something that I’ve only just recently learnt to do myself having encountered this problem on a project I’m currently working on. I was using my ultra-wide 14-24mm lens and I needed a way to correct some of the keystoning. I figured the distort tool might just work, and it did. I’d played around with the distort tool for fun and it’s a great way to learn Photoshop. To save you discovering this by accident however, I thought I’d share what I learnt. I hope you find this video helpful. The quality of the video was great until I uploaded to WordPress so I guess WordPress is heavily compressing the video. I think you can still follow it however..
Sometimes of course, the keystoning effect can add greatly to the impact of a picture and you wouldn’t want to straighten the vertical or horizontal lines but other times straightening the verticals is the way to go.
This is the corrected picture, the converging verticals straightened out using the tools in the tutorial video and I think it’s an improvement. It’s opened up the picture and is a more accurate representation of the way I saw the cathedral..