I am approaching this subject from the perspective of landscape photography, which is just one of many uses cases. Other use cases will be discussed separately.
Tilting, swinging and shifting, or using a more general term, camera movements, refer to actions taken that change the orientation of either the front lens of a camera or the film (sensor) plane, or both.
These camera movements provide a means to control the area of an image in sharp focus and to control perspective / distortion. Tilting the lens forward is used by landscape photographers to get what appears to be an infinite depth of field. Tilting it back is used to make a scene look miniaturized. Swinging the lens either left or right can bring some object crossing the image diagonally (like a fence) in focus from beginning to end. Tilting and swinging the backplane is used by architects to remove key-stoning, and by landscape photographers to enlarge or reduce the size of objects near the “edges” of the image (e.g., to enlarge the bottom of the image, and thus shrink the top of the image, which usually correspond the the ground and sky respectively). Shifting is used to move the image up, down, left or right on the film plane. This is useful when making panorama shots.
Three technologies are commonly used that enable these movements: specialized tilt-shift lenses; view cameras; and software. Software is relatively straightforward to use, and thus the easiest to execute, requiring little manipulation of the camera or lens, therefore it is not really relevant to this study1. As well, while movements of the back plane are important, I will leave these for a follow-on article. This leaves us to focus on lens movements.
I find it is helpful to understand the theory behind each movement as it helps me visualize what’s going on. There are two theories at play: the Scheimpflug Rule and the Hinge Rule. Harold Merklinger explains “The Scheimpflug Rule and the Hinge Rule are surprisingly similar. Both rules state that three2 fundamental planes must converge along a common line.” (LensNotes 2019)
The relationship between lens movements and the plane of sharp focus is shown in the following animations.
In the normal case, the film plane (sensor plane) and lens plane are parallel to each other. As a result, so is the plane of sharp focus, which is blanketed by a zone before and after it that is also in “acceptable” focus.
We know that we can move the plane of sharp focus closer or farther away by adjusting the focus ring and we also know that the depth of the zone (DoF) can be narrowed or deepened by opening or closing the aperture. Keeping things simple, we might visualize this area in focus as a rectangle.
When we tilt or swing the lens, the relationship between the formerly parallel planes changes dramatically. According to the Hinge Rule all five lines intersect at the hinge point. When the lens is tilted downwards, the hinge point is below the camera; when the lens is tilted upwards, the hinge point is above the camera. This hinge point is located on the lens plane, below or above the lens. Similarly when we swing the lens left or right, a hinge point is located on the corresponding side.
It is important to highlight that the once parallel lines that bounded the near and far limit of “acceptable focus” also go through this hinge point. What this means is that this area is no longer a “rectangle” but it is now a wedge, whose narrow end starts at the intersection point and expands out from there.
In the typical landscape use case, the subject of our photograph is usually the horizontal land in front of us with some taller subject in the distance. If the objective is to have as much of the subject matter of the scene fall within this wedge of focus, then the question is how do I control the shape and orientation of this “wedge” to ensure everything fits in? As with the normal case we are familiar with, the focus ring and the aperture ring, have a role, and tilt becomes a third, and new, parameter in the equation. The interaction among these parameters is however complicated and thus results are often come by through trial and error. Notwithstanding, the basics are:
- Aperture (f-stop) adjusts the width of the wedge, which parallels the normal case where the aperture adjusts the depth of field. The smaller the aperture, the wider the wedge, or the deeper the depth of field
- Focus distance adjusts the angle of the plane; in the normal case it adjusts the distance from the lens of the plane. With a tilt, focusing close creates a steeper angle, focusing far away shallows the angle. Focusing at the hyperfocal distance creates a wedge where the Far Limit of DoF will skim the ground.
- Tilt adjusts the distance of the hinge point from the camera. The smaller the tilt, the greater the distance is the hinge point from the camera and thus the steeper the angle of the plane of sharp focus. This makes sense as, as the distance to the hinge point approaches infinity the lines all become closer to parallel.
- While Focusing distance and Lens Tilt both effect the Plane of Sharp Focus, they do so in different ways. The tilt sets the hinge point and once set (by the tilt angle of the lens) it remains fixed. Focus then adjusts the angle of the plane with that single point point fixed; that point the plane is hinged to.
Future articles in this series will report on the application of the rules.
References:
LensNotes. 2019. “Principles of View Camera Focus by Harold M. Merklinger.” Lens Notes. Lens Notes. September 16, 2019. https://lensnotes.com/articles/principles-of-view-camera-focus/. (LensNotes 2019)
LensNotes. 2023. “Scheimpflug Principle.” Lens Notes. Lens Notes. July 23, 2023. https://lensnotes.com/photography/scheimpflug-principle/. (LensNotes 2023)
“Lumariver Depth of Field Calculator.” 2016. Lumariver.com. 2016. https://www.lumariver.com/lrdof-manual/. (“Lumariver Depth of Field Calculator” 2016)
Merklinger, Harold. n.d. “FOCUSING the VIEW CAMERA.” Accessed January 22, 2024. https://www.cs.cmu.edu/~ILIM/courses/vision-sensors/readings/FVC16.pdf.
Photography Skool. 2021. “Tilt Shift Lens, Tilt Function Visually Explained.” YouTube Video. YouTube. https://www.youtube.com/watch?v=zfW1vKSbpvc. (Photography Skool 2021)
“Using Tilt-Shift Lenses to Control Depth of Field.” 2020. Cambridgeincolour.com. 2020. https://www.cambridgeincolour.com/tutorials/tilt-shift-lenses2.htm. (“Using Tilt-Shift Lenses to Control Depth of Field” 2020)
Zigunov, Fernando. 2019. “Scheimpflug – Tilt-Swing Adjustment in Practice.” Zigunov Aero. Zigunov Aero. July 22, 2019. https://zigunov.com/2019/07/22/scheimpflug-tilt-shift-adjustment-in-practice/. (Zigunov 2019)
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