There a little thing called "Perspective" that can drive a landscape photographer nuts. Beyond the whole idea of framing the subject, including things, excluding others, ensuring only the most critical objects are in view, is the relationship between the objects. That's point perspective. Along with placement, there's the whole size relationship between the objects that has to be considered when shooting a scene. There are lots to consider when dealing with perspective and I'll deal with a couple in this monthly article.

First and foremost before knowing how to deal with perspective you have to realize what drives perspective. While many may see field of view of your lens as the primary driver, that's not quite correct. Sure, perspective appears to change when you move a zoom lens from a narrow to wide field of view and move closer to compensate. But, what's changing perspective isn't the increase of field of view--the subjects appear to be smaller but the relationships are still the same--it's the distance. By moving closer, you're changing the relationship between your subjects and at the same time the perspective. I guess you might think from a practical point of view it's one in the same but it's not.

Consider a scene taken with a 35mm full framed camera. Then from the exact same location and exact same lens you shoot with a Nikon digital SLR with its 1.5x crop factor. While the field of view of the second image is different--it's smaller--the relationship between the subjects are exactly the same. They're a bit smaller in the full framed image but the relative sizes between the elements of the image are exactly the same. The perspective is exactly the same.

Once you know this little tibit but critical point, you now know what to do to change perspective--whether through cropping like our example, or by simply moving your feet and adjusting your distance.

Let's go through couple of examples.

• Say you like a particular perspective but don't like the field of view your setup captures. You like how the elements of the scene play with each other and think their realtive sizes are correct. This means you're tripod is located on the right spot. On the other hand the field of view isn't correct. You can't see enough or you see too much. What do you do? You change the lens and don't move your feet. In practice out in the field you can do this by approaching a location and without even pulling the camera up to your eye move your feet to adjust the relative sizes of the elements in the scene by going forward and backwards. Once you've got the relative sizes correct, start thinking about framing and what lens to use. If you find me out in the field at this stage you might see me using my hands as frames trying to determine what to include and exclude. Once that's done, I choose the lens to capture the right field of view and depth of field. I then incease my relative sensor size and increase the field of view by stitching files together or crop the image to decrease the field of view while essentially keeping the depth of field static. Once that's settled, I pick the right aperture to set the depth of field I want.

Note: This might not be commonly known. If the subject size and aperture are kept constant through a focal length change--this means you're moving your feet to keep the subject size constant--the depth of field surrounding the subject is the same before and after the lens change. The thing that's changing is perspective. Now you're wondering why 50mm images don't look the same as 500mm when it comes to depth of field. How do you get those completely out of focus backgrounds on the 500 but find it harder with the 50? Essentially the 500 goes out of focus faster the further you get away from your focus distance than the 50. For you math geeks out there, it's an asymotoptic relationship. The wider the shorter the lens the more in focus things will appear even though mathematically the depth of field is the same.

• Say you're highly restricted by shutter speed and have to set a high speed to freeze action--the aperture is set in other words--you know what subject size you want which makes perspective the only variable by adjusting your camera to subject distance. If you want the size changes between the elements of your image to be relatively similar you go far away to where the changes in distance between the elemenst are relatively small. Then you choose a long lens to frame the image correctly. If you want a significant change in relative sizes, you pick a short wide-angle lens to get close. Of course the fixed aperture means your depth of field is constant regardless of the perspective change though those really nice blurred out backgrounds as noted above may be a problem if you choose an especially short lens.

Let's look at my examples at the top of the page. The left image was stitched together from four shots made with a 28-70mm f/2.8 AF-S lens set to approximately to 42mm's. The right image was made from three shots taken with a 14mm f/2.8 ED-IF. The compositions are essentially the same. The primary subject--the Joshua Tree on the left--is about the same size in both images. The relative sizes of the mountains in the background are significantly different between the images. This highlights the perspective change by moving closer from the left to the right image. The Joshua Tree is the same but the relative sizes of the other elements are totally different between the compositions.

You've probably seen the same affect when making portraits. Using a wide-angle lens forces you to get close to make the head the appropriate size but the perspective totally skews the image; the noses are large, the ears small. On the other hand, using a short telephoto lens lets you retreat a bit making the portrait look a bit more natural and honestly more appealing.

Even though perspective may look like a matter of field of view, it's really all about the distance from your camera to the subject. When seeking a specific perspective, first set the distance then adjust your lens selection to frame the scene correctly.

Cheers

Tom