Virtual horizon

A kind of on-screen spirit level that shows you when the camera is level. This can be useful in landscape photography, for example, when the horizon isn’t flat or visible. Some also have fore-and-aft levels to help avoid any tilt (and converging verticals) when shooting buildings.

ViewPoint (DxO)

Software that corrects distortion using lens correction profiles, fixes volume deformation created by wideangle lenses and offers perspective correction tools for fixing converging verticals and more. Works as a standalone app or as a plug-in and also integrates with DxO Optics Pro. See also: DxO ViewPoint 3 review

Upright tool (Lightroom)

A set of perspective controls which can correct converging verticals, skewed horizons and other perspective problems. Lightroom offers a set of automated one-click buttons which often fix the problem immediately, plus a manual tool for correcting more complex or difficult perspective problems.

Transform

Changing the perspective or scale of a photo or objects within the photo. Typically it can include straightening, scaling up and down, skewing or correcting converging verticals, for example.

Tilt-shift

A specialised type of lens which can be tilted relative to the camera body. This changes the plane of sharp focus and can be used to extend or contract the available depth of field. It can also be simulated digitally using tools which leave a central strip of the photo in sharp focus but progressively blur the rest of the image towards the edges.

Straighten

It’s very easy to accidentally shoot with the camera slightly skewed so that horizons or vertical objects aren’t straight. Most photo editing apps have a simple Straighten tool to put this right.

Perspective correction

A means of correcting converging verticals in architectural shots and other perspective issues. You can get ‘perspective control’ lenses which use complex lens adjustments to fix the problem optically, or you can use software with perspective correction tools.

Perspective

A broad term to describe the effect of your shooting position and the lens’s focal length/angle of view on the appearance of the objects in your photo. Wideangle lenses tend to exaggerate perspective and convergence, e.g. converging verticals, because you tend to stand closer to your subject and tilt the camera more away from the horizontal, e.g. to get tall buildings into the frame.

Keystoning

Where the tops of tall buildings appear to converge. This happens when you’re so close you have to tilt the camera upwards to get everything in. You can correct it by choosing a more distant viewpoint and keeping the camera level, or by using keystone correction tools in software.

Converging verticals

A type of perspective distortion caused by tilting the camera upwards to photograph tall buildings. It’s worse with wideangle lenses because they let you stand closer, so you tilt the camera even more. The only solution is to compose the shot with the camera completely level.