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Monday, March 1, 2004

Perspective & The Nature Photographer


How To: Add perspective control to your photographic tool kit for straighter trees, upright buildings and towering cliffs


Perspective & the nature photographerDo you ever wonder why some of the classic photos of stands of trees or tall cliffs look so majestic compared to the results most people get with their cameras? Ansel Adams, Eliot Porter and other masters of the landscape often brought a different perspective to their images, and this perspective isn’t about their creative eye.

Sometimes new photographers confuse the technology with the photographs when looking at classic work. Adams,Porter, Hyde, Weston—all of them photographed with large-format view cameras, so the thought is that this grand scene of majestic subjects comes from using a large-format camera, and 35mm (or digital cameras) can never match it.

That's not exactly true. A view camera can offer unique features and a stunning transparency or negative. However, when we look at classic images that make trees look like Greek columns or grand landmarks with a stately air to them, we're often responding to the photographer's control of perspective in the image. The view camera makes this quite possible to do, but if you understand the principles involved, you can gain control over perspective in your photos, too, regardless of your equipment.

We'll look at perspective control from four points of view: view camera controls, specialized lenses for 35mm, wide-angle shooting and computer corrections. First, let's look at perspective in the landscape.

Perspective is a fact of life in the world. Close objects are larger than big objects farther away, which is one way we judge distance. Parallel lines are wide near you and seem to converge toward a single point in the distance; a classic example is railroad tracks.

This happens with trees, too. Trees are vertical, often parallel lines. When you stand even with the base and look up, the closer parts of a tree are largest. They get smaller with distance and the "parallel lines" no longer look parallel. They converge, making the tree lean inward and backward.

This can be a dramatic effect if you get in close and use a very wide-angle lens. However, when shooting with more normal focal lengths, the trees just lean in a little as long as you're pointing the camera up; this lessens the feeling of height and majesty. Similar effects happen for nearly any subject that has some height, even to the effect of cliffs or ruins looking like they're leaning over backward.

The only way to correct this when shooting is to keep your camera back (the "film plane") parallel to your subject. This way, there's no perspective change to the subject from bottom to top.

However, this isn't always possible. Often, you have to shoot from below trees or a cliff, meaning your camera has to point upward. So the lines will converge, losing the majestic feeling you might have been after.

Perspective And The Standard Camera
There are three ways of correcting perspective with the average camera: shooting straight on to the subject, using perspective-control lenses and shooting with a wide-angle lens.

As mentioned above, it isn't always easy to shoot a subject straight on. However, if you look around, sometimes you'll find that you can get some height so you can point your camera directly at the subject. You need to be able to set up the camera with an absolutely vertical back, tilted neither up nor down. This will ensure the back is parallel to the scene. Any camera will work for this. It can be worth a try.

Using a telephoto lens on the scene can make it easier to keep the perspective straight. To fill the image with the subject when you use a wide-angle lens, you often have to get so close to the subject that you're forced to point the camera upward. With a telephoto focal length, you have to back up, which flattens the angle at which you have to shoot, making the camera back closer to parallel to the subject. Naturally, not all subjects can be photographed this way, since you can't always back up enough to include the whole scene.

Perspective-control lenses make this a little more straightforward. Canon and Nikon make them for their cameras in a range of sizes from wide-angle to telephoto (the wide-angle lenses are probably more useful for the nature photographer).

Regardless of the focal length, the important thing is that the lens shifts up and down, as well as side to side. This allows you to set up your camera straight on to the scene, even though the subject is higher than the camera (or lower—these effects also show up if you point the camera down). If you looked through the camera at this point, you probably wouldn't see the whole scene; you'd want to tilt the camera up.

But you don't have to! Now, you simply shift the lens itself upward until you can see your desired composition. Obviously, this is best done on a tripod. The back of the camera is still parallel to the subject, so vertical lines stay vertical, and trees and cliffs look majestic.

You actually can shift the lens in horizontal dimensions, too, for special purposes. A common benefit of this is when you're limited in the space available for shooting a scene. Angling the camera may give you more perspective than desired, so set the camera parallel to the scene and shift the lens to one side to gain the composition needed.
—Rob Sheppard

Perspective And The View Camera
The ability to move parts of the camera separately is a primary determining factor when selecting the view camera as a tool for landscape photography. The lens on a view camera moves independently of the back or film part of the camera body and is capable of controlling perspective. With these movements, a photographer can correct or manipulate the appearance of the final image.

The first thing I do in the field after determining a composition is make sure my camera is level, front to back and side to side. There are horizontal and vertical lines on the ground glass, but often there are no parallel lines in the field with which to line them up. Small bubble levels attached to the tripod head or camera work well. I've tried eyeballing, only to see images flow off the frame when I get my film back from the processor.

A number of technical movements on the view camera can then be used to control perspective. In using these movements, don't let the physics of "bending" light bog you down. It's important to realize that what you see on the ground glass is what you're going to get on film (providing it's properly exposed).

The most important movement for perspective is rise and fall. This allows you to move the lens up and down (or the back of the camera) while keeping everything else locked down.

If my composition requires more room at the top of the frame, to include dramatic skies over of a stand of trees, for example, I'll use the rise function on my camera. The rise essentially lifts the lens up while the camera back stays level. The trees remain parallel to the sides of the frame. Simply tilting the camera up to include more sky will produce converging lines, which will lean toward the center of the frame. Naturally, I reverse these techniques if I need more space at the bottom of my composition.

Keep in mind that these movements are suggestions to make images appear parallel and "square." However, I'm a
proponent of breaking the rules. If you want trees bending toward the center of the frame, or want to exaggerate perspective by manipulating movements, go for it. It's all a part of controlling the perspective the way you want. Aperture adjustment may be necessary to accommodate film and subject planes, but you can determine your limitations simply by looking on the ground glass.

The technique applied to rise and fall also holds true with horizontal movements, called shifts. A shift moves the lens to the right or left, allowing more room on either side of the frame while keeping horizontal lines on the film and subject planes parallel.

The rise, fall and shift movements are effective techniques to keep your vertical and horizontal lines in perspective. Another useful and often utilized function of the view camera is the front tilt, which enables you to get foreground and background items in focus when a small aperture isn't enough.

By tilting the front of the camera down, you're given an extended range of focus from near to far (the plane of focus is tilted). You can determine how much depth in sharpness you've gained by looking at the ground glass and refocusing after tilting the lens. It may take a few adjustments to get the maximum effect, but you can see it all unfold on the ground glass. You do have to be careful of where the plane of focus cuts through the image. It's possible to have flowers in the foreground and mountains in the back sharp, yet the tops of nearby trees out of focus.
—Gary Alan Nelson

Perspective Control In The Computer
If your image is already shot (maybe you have old images that need a tweak of perspective adjustment) or you can't use any of the techniques discussed so far, you can make perspective corrections in the computer. These corrections are easy to do, but not necessarily easy to do properly. Most image-processing programs offer some sort of perspective-control function (although Jasc Paint Shop Pro has one of the most controllable perspective features on the market).

Here are some ways to do it in most imaging software. You'll have to check to see how your specific program works.

1 Crop Tool. On a number of programs, there's a perspective function associated with the Crop tool. If this is checked, you can drag your corners in or out to correct perspective. While you could add a grid or guideline to the photo to check lines, an easy way of doing this in many programs is to move in the side crop edge next to the part of the subject that you want to correct (next to a tree trunk, for example). Now, move the corner of the crop box in until the line is parallel to the subject. This gets the angle right. Then move the crop edge out to the correct crop position and make the crop. The perspective is corrected automatically.

2 Perspective Transform. In programs with Layers, you typically can transform a layer with perspective control. Make your photo a layer, then find the Perspective tool (it could be in the Edit, Image, Layer or other menu). Adjust the corners of the photo to straighten your subject. A guideline or grid can be very helpful (check your program's Help function to see how to add them; Grid is often under the View menu).

3 Jasc Perspective Correction Tool. Jasc has added Perspective Correction as a tool in the toolbar. Simply use your cursor to place a "box" around your subject, then line up the corners of the box with the points on your subject that need to be straightened. Hit Enter and the computer does the magic.

4 Doing It Right. One problem with any of these tools is that they ignore an issue of perspective. When you look at something from below, for example, you can see more of its bottom than its top. So if you straighten the subject, it will still have some of that proportion, resulting in a squatty object that really doesn't represent the subject.

You need to stretch the scene upward (assuming the correction has been made vertically) to compensate. Use the Transform Scale tool, or you can resize the photo by making only the vertical dimension larger (uncheck Constrain Proportions in Adobe products—and remember to recheck later!). This can be tricky since there are no precise scales for the adjustment. Either do it visually so it looks right or compare it to an unadjusted photo to see if the subject has the right proportions.
—Rob Sheppard

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