Today we’re going to delve into the topic of focal length and how it relates to architectural photography. There’s a lot of info already on the web explaining what focal length is (some of it quite technical because it’s all about optics). So we’re not going to repeat what’s already out there. Instead we’re going to use a couple diagrams to explain how the focal length of a lens affects field of view and what it means in a practical sense to architectural photography.
The diagram below shows three lenses with different focal lengths. We have used a web tool to calculate the angle of view each lens will have based on 1.5 crop factor (The angle of view changes based on the sensor size of the camera). The important thing to note is how a small focus length provides a larger field of view and visa versa.
Below is a practical example of how the focal length and the field of view of lens affects architectural photography. The diagram below represents a small room with the field of view of several different lenses. The lenses with larger focal lengths like the 28mm and 70mm show little of the room. It is only when a lens with small focal length like 10mm is used that the entire wall of the small room can be seen. This is why interior architecture is often shot with lenses with small focal lengths (24mm and lower). These types of lenses are called wide or ultra wide angle lenses. A couple examples would be the Canon 10-22mm or the Canon 17mm TSE.
A second example is shooting the exterior of a building that is in a tight alley way. If there wasn’t a building behind you then you could just walk backwards until your 28mm lens has enough distance to capture the entire building, but in this case you can’t move backwards so changing to a wide angle lens (small focal length – large field of view) will allow you to capture the entire building facade and also some of the neighboring buildings.
What you may be thinking at this point is why you wouldn’t just use a wide angle lens for every shot. Well all lenses have compromises. What a wide angle lens does is cram a lot more of a building into a single frame. This affects the proportion of your shot. As a general rule I try and use a 24mm lens, which is a sweet spot for many architectural photographers. It is only when physical limitations like the ones above that I change over to a wider angle lens (or if for some particular reason I want the style of shot a wide angle lens delivers).
A point I often make about camera selections for architectural photography is that unless your camera has a lens with a small focal length then you’re going to be limited when it comes to interiors. Many fixed lens cameras for example have focal lengths around the 28mm mark. This is why choosing a DSLR is a much better option because of the ultra wide angle lenses available.
As a closing note I should mention that focal length affects more than just field of view. Magnification, image sharpness and bokeh (Background blur) are also factors to consider. I should also mention that this post focused on wide angle lenses, but there is an inverse conversation that could talk about zoom lenses and architectural details. But we’ll leave that conversation for another time.