Focusing a View Camera ABCs, and One Still Life Example

This is an 'ABC' article. There are far more detailed treatises available elsewhere that explain view camera focusing, complete with calculations and focusing equations.

All conventional cameras (with the limited exception of those equipped with tilt-shift lenses, or flex-bodies) focus on one plane only. That plane of focus is always parallel to the lens plane and to the film plane. Suppose we want to take a picture of a field of flowers stretching from our feet to the horizon, and we want to include a mountain on the horizon. We want everything in focus, and we want those flowers at our feet to look big in the final picture - which means that our lens has to be very close to the flowers. If we set up our 35mm digital camera, for instance, pointing straight ahead, we run into some trouble. Since the camera is pointing straight ahead this means that the film plane and the lens plane are vertical. As a result of this, we can only focus the camera along a vertical plane. So, if we focus on the flowers near our feet, everything beyond those flowers goes out of focus. If we focus on the middle of the flower field, the mountain and the flowers near our feet go out of focus. What to do now? Well, we can stop-down our aperture to get more depth-of-field. What is 'depth-of-field'? As a lens aperture gets smaller the area behind and in front of the focus point move into focus. If you focus on somebody's eye with your lens set to f1.4, only the eye will be in focus in the final picture, with the rest of the face relatively blurred. If you shoot at f5.6, more than likely the person's face will now all come into focus but the background will remain blurred. If you shoot at f22, the person's face and all the background will come into sharp focus. What you have done here is to increase depth of field. Longer lenses seem to have shallower depth of field than shorter lenses. This effect has more to do with their field of view rather than to any changes to depth of field per se. Returning to our example, we find that the smallest aperture on our lens is f22. Using our depth-of-field scale marked out on our lens, we set the focus, stop the lens down to f22 and take the picture. As we look at the LCD we are disappointed to see that the mountain and the flowers near us are still out of focus: we don't have enough depth of field. Maybe we can point the camera down a bit? Sure, but we'll cut off our mountain. What is worse for small format cameras is that by using our smallest lens aperture we degrade the image quality too owing to lens diffraction effects. Lens resolution at small apertures is limited by light diffraction through the small lens opening - a fact of life for all lenses. So we're stuck. We need a view camera.

View cameras can focus on any plane we choose. How do they accomplish this feat? They do so by attaching the lens and the focusing screen/film to front and rear moveable standards respectively (standards are vertical pieces of metal or wood) that are separated by a light-tight accordion-like bellows. We can tilt each standard forward or backward, we can raise or lower the standards, we can shift (slide) them left or right, we can swing them left or right, and we can move them closer together or further apart. Front standard movements affect the focusing plane only. Rear standard movements affect the focusing plane AND introduce perspective distortion. Below is an example of what a view camera can look like. Unlike 35mm or medium format or digital cameras which basically all look alike, there are a huge number of different view camera designs. This is Linhof's example of a state-of-the art design for a modern view camera with an asymmetrical L-shaped standard, the 4x5 GTL Kardan Master. Some photographers prefer folding wooden cameras, or other types. We prefer an Arca Swiss design.




As we alluded to earlier, when the object plane, the film plane, and the lens plane are all parallel, the object can be brought into sharp focus by varying the distance between the lens plane and the film plane. This is true for any camera. But what happens when we tilt a view camera lens forward, for instance? Won't the object we focused on go out of focus? Well, it all depends on the plane the object occupies. For example, suppose we focus on a tree by sliding the standards closer together or further apart. The tree exists largely in a vertical plane, so most of the tree will be in focus once the standards are parallel to the tree. If we were to now tilt the front standard forward, we would be altering the plane of the lens closer to horizontal thereby making most of the tree go out of focus. Returning to our flower field example, it is apparent that most of the picture exists in a horizontal plane. The flowers are not very high off the ground, the ground is flat to the horizon, and the mountain does not look too high because it is far away. With a conventional camera we can only focus in a vertical plane. If we use a view camera, however, we simply tilt the front standard (the lens) forwards, thus bringing the lens focusing plane near horizontal. The whole scene, from the flowers right in front of the lens to the distant mountain, suddenly pops into sharp focus. We don't even have to use a smaller aperture if we don't want to, which can be useful if there is a wind blowing the flowers around. A view camera would allow us to take the picture with a large aperture and a fast shutter speed, thus freezing the flowers. With a normal camera, we would have no choice but to use a small aperture and thus a slow shutter speed. The flowers would then appear blurred because of movement in the breeze.

A basic principle of view camera focusing was codified by an Austrian Captain, Theodor Scheimpflug, in 1904 as part of his research into minimizing perspective distortion in aerial photographs. The rule now bears his name. Essentially, the rule states that if a tangent is extended from the image (film) plane, and tangent extended from the lens plane, the point at where they intersect with a tangent extended from the object will render the object in sharp focus. So, if our object is along a horizontal plane like our flower field, and the film plane is vertical, if we draw tangents to these planes, they intersect at a right angle. Now, when we start slowly tilting the lens forward, the plane of the lens will eventually intersect with the film plane and the object plane. At this point the entire scene snaps into focus. A diagram below illustrates this principle. Of note, the focusing plane is only altered by tilts, or by swings, and not by other movements of the standard.




Most 35mm users don't know how their cameras focus. It is actually a very simple case of the lens assembly moving back and forth inside the plastic (or metal, depending on the wonderfulness of your lens) lens casing as the camera autofocuses, or as you turn the focusing ring. More expensive lenses have internal focusing so you don't see what's going on, and that your filter ring does not rotate as you focus. If you focus on an object close to you, the lens assembly moves outwards, or away from the back of the camera where the film or digital sensor lies. If you focus on an object far away from you, the lens assembly moves closer to the film plane. Longer lenses need to move their lens assemblies further away from the film plane to focus nearby objects than shorter lenses. This is why all 35mm digital or film lenses have 'minimum focusing distances' listed. It is, in fact, a manufacturing tradeoff. The minimum focusing distance for most 300mm lenses is about 1-2 meters, depending on the lens. The lens will not focus on anything closer than this distance. You would need a REALLY long lens casing for such lenses to focus a closer object: not something you would readily walk around with. View cameras focus in exactly the same way. Move the standards closer together to focus objects at infinity, or far away, and move the standards apart to focus on nearby objects. How far you can move the standards apart depends on the length of the bellows between them. You can swap out short bellows for long ones if macro photography is your fancy. We routinely focus our 240mm lens on objects less than an inch away with a long bellows. Also note that moving the standards closer together or further apart does not alter the plane of focus. You need to either tilt or swing the standards to do that.

For our still life photograph, we wanted to keep the standards parallel to the front of the rose while at the same time keeping the camera off to the side. We also wanted to use a wide aperture for a shallow depth of field. As demonstrated in the picture below, the camera had to be positioned some way above the keyboard, and off to the side because, gee, we didn't have room to put it anywhere else. From the finished picture it seems as though the camera was positioned almost along the keyboard, level with the rose, and just to the left of the rose. We got this effect by altering the position of the front standard. We simply dropped the front standard into a lower position, and shifted (slid) the front standard to the right. Shifting the front standard can be a great trick in such situations as photographing near a busy roadway. For example, we can take pictures that look like they are taken from right in the middle of the roadway, whereas in fact we are safe and sound standing on the sidewalk! Now back to our still life. After we had the framing right, we then focused the camera on the centre of the rose by moving the standards away from each other. The rose centre came into focus, but everything else remained out of focus. To get the plane at the front of the rose into focus, we either had to apply the Scheimpflug principle, or instead, align the front and rear standards so that they were parallel to the plane at the front of the rose. We opted for the latter option. We swung the front standard a little to the left, and we swung the rear standard to the left by the same degree. Most of the front of the rose now came into focus. However, the top and bottom of the rose were still out of focus. Why was this? Notice that the camera was tilted downwards, thus looking down at the rose. Although the standards were now parallel to the rose front on a horizontal plane, we had not yet corrected for the vertical plane. This was a simple matter of tilting the front standard backwards to vertical, and by tilting the rear standard backwards too by an identical amount. The entire front of the rose now snapped into focus. We then stopped the aperture down a teeny bit to get a couple of the piano keys into focus, and then we took the picture.




This has been a brief introduction into focusing a view camera with an easy example. We will do another article at some point illustrating the use of perspective distortion in large format landscape photography.

- August 2007.