Perspective Correction

Converging verticals occur as soon as the sensor plane is no longer parallel to the facade — in other words, whenever the camera is tilted up or down. The building's verticals then converge in the image. This is not a malfunction of the lens, but simply projection geometry; however, it can be corrected at two points in the chain.

Optically On Set

The clean solution is the perspective control lens: the camera remains exactly horizontal, horizon in the center of the frame, sensor plane parallel to the building. Then the lens is shifted upwards — the image circle of the lens is larger than the sensor, and the shift brings the top of the building into the frame without changing the geometry. The verticals remain parallel, and full resolution is maintained. The prerequisite is a tripod with precise leveling; shooting handheld makes shift work a matter of luck.

Digitally In Post

The distortion in compositing or grading mathematically tilts the image back: the image is distorted into a trapezoid and re-cropped. This works, but it costs visibly — the cropping eats up image area, scaling eats up resolution, and with strong correction, textures in the upper third of the image appear softly rendered. Therefore, those who know that distortion correction will be applied shoot with a buffer in the frame and at a higher resolution than the target format. For moving shots, the correction must also remain constant over the movement or be tracked.

• Rule of thumb: What can be solved on set with a spirit level and shift, don't push to post.
• For planned post-distortion correction, shoot at least one resolution level above the target format and leave headroom at the top of the frame.
• Slight converging verticals can be intentional — monumentality, threat. First decide if the tilt tells a story, then correct.