This post is an intro into perspective control of architectural photography.
Below is a diagram that illustrates what is meant by a perspective correct image and what is meant by a building that is falling away. The building on the left has vertical lines that are parallel (Perspective correct), while the building on the right has vertical lines that are converging (Falling away). The general orthodoxy of architectural photography is that an image should be perspective correct. That is the type of image that magazines typically require and photographers spend a lot of money on specific cameras and lenses to ensure they can achieve this. But what if you don’t have this type of equipment? Don’t worry, we’ll show you that it’s not the special equipment that is producing perspective correct images, it’s actually the angle of the camera. Which means anyone can create basic perspective correct images.
To understand this let me explain how you create a perspective correct image. Basically all you need to do is make sure your camera is perfectly level. You can do this by using a level that sits in your flash mount or you can use the leveling tools provided in new model cameras.
When the camera is perfectly level it’s view plane will be parallel with rectilinear buildings and this will produce perspective correct images.
If however you tilt your camera up, which is typical when you’re trying to fit a large building like a skyscraper into your frame, then you end up with the camera’s view plane being skewed to the building and this results in the building falling backwards in the photo. Why? Well if you have ever done perspective drawings by hand you’ll be familiar with the rule that things that are further away become smaller. When you tilt your camera up the distance between the top of the camera’s view plane and the bottom is no longer equal. The distance at the top is larger and therefore the top of the building becomes smaller in the photo. Even a very small angle change in the level of a camera will result in an image not being perspective correct.
What this means is that you can achive perspective correct images with any lens as long as you keep your camera level. There is one problem with this though. When you keep your camera perfectly level a large amount of your photo real estate is taken up by the ground. This is why you were tilting your camera up in the first place. So you have ended up with a perspective correct image, but you can’t see the top of the building. This is where tilt shift lenses come in because they allow you to keep your camera level (Which produces the perspective correct image) but they also allow you to mechanical move the lens so you can fit the top of the building in. I’ll write a separate post on tilt shift lenses, but for now i’ll leave you with two work arounds. The first is to use software like Photoshop or Gimp (The free alternative to Photoshop) and to correct perspective by distorting the image. The second is to crop down an image. You take a perspective correct image using a wide angle lens or by simply moving backwards from your subject building. What you end up with is far more content in the frame then you wanted, but it means you can crop the image so that you remove the majority of the ground and focus on the building. You’ll compromise the megapixels of the image with both of these techniques, but you will end up with perspective correct images without having to buy very expensive equipment.