Perspective Control in Architectural Photography
One of the elements of architectural and interior photography that causes the most confusion is the concept of 'tilt and shift'. This is a form of lens perspective control that allows lines within an image to remain parallel, leading to a more visually pleasing photograph.
Notice how in the photo below, shot for Fletcher Priest Architects, the vertical lines of the building remain parallel, despite shooting the top of a tall building from ground level. The vertical lines do not converge as they get to the top:
This also works well for interiors. The parallel vertical lines below lead to a cleaner, more balanced image:
To show this even more clearly, below is a building shot without perspective control (looking up at the building) vs using shift to control the converging vertical lines. I have drawn the converging lines in red to illustrate.
Ok, so perspective control by shifting can lead to more pleasing looking shots - but how does it work, exactly?
I am going to use my Cambo Actus technical camera to explain how it works. However, it is exactly the same idea with DSLR tilt/shift lenses.
Light enters the lens from the front, travels through it, and is then projected as an image circle, which is larger than the rectangular digital sensor, or film. This rectangle crops the image circle, and captures a section of it. Architectural lenses have a particularly large image circle. In effect, your lenses are much wider than you think! The sensor rectangle is just a small crop of the overall image, as illustrated below.
When shifting, all we are doing is moving the sensor rectangle around this image circle. This allows us to crop higher, lower, more left, or more right within the circle; it is effectively the same as looking up, down, left or right, while keeping the camera completely level.
Below is a video of me explaining the concept.
Ok, I get it! But how does stitching work?
Well, two shots, taken from opposite sides of the image circle, can be stitched together to make a super wide image. Below are two shots from a recent shoot of a Carvela shoe store. The first image is taken shifted fully to the left, the second is taken fully to the right. Notice there is an overlap of where the images meet in the middle of the space.
Many of you will have seen the tilt/shift lenses made by Canon, Nikon etc for DSLR style cameras. With these lenses, the concept is exactly the same. The only difference with this system is that the image circle is being moved, rather than the sensor rectangle. This means that unlike my technical camera, the two images do not perfectly line up. This doesn't mean they are useless for stitching - it just means more work in Photoshop!
Ok, that's 'shift' explained, what about 'tilt'?
Well, that's where things get complicated! My advice would be to look online for the Scheimpflug principle. There are people on the net far better at explaining this than me! But essentially it is a way of gaining a much larger focal plane, while using a wide open aperture. This is particularly useful for still-life photography, and can result in astonishingly detailed photos.
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GG Archard is a London based photographer of architecture and interiors. He is regularly commissioned to shoot real estate, design, hotels, furniture, art installations and the built environment both in the UK and internationally.