Flattening the image, or compressing the image, is a nice result achieved when you use a telephoto lens and are situated a distance from your subject. I used this effect to make a romantic engagement photo in the Bayard Cutting Arboretum of my newly engaged niece and her fiancé.
The trees in the distance appear much closer than they actually are. And all the “layers” of background objects appear large and stacked closed together. The closest and furthest objects fall out of focus due to the depth-of-field. I like the compression effect as it gives a very clean and almost painterly feeling to the background that might otherwise be too distracting and take away from the subjects in the frame.
This post by photographylife.com has a great explanation of the effect: “This combination of long lens and camera-to-subject distance gives the viewer the impression that distant objects are larger than they actually are. As a result, it gives the appearance that the background is pulled in closer to the subject. The opposite effect occurs when you use a wide angle lens. When we use a wide lens, we tend to stand much closer to our subjects compared to a telephoto lens. Because of this relative closeness, near objects will look proportionally larger than objects in the distance. As a result, the background elements become much smaller and seem farther away.”
I used a moderate telephoto lens, the Tamron 70-210mm F4, on a crop-sensor camera at 170mm, so my effective focal length was 255mm. I stood a distance away and actually used hand signals as they couldn’t hear me. The effect will be more dramatic by standing even further away and using a 300mm or longer telephoto setting. Next time you are headed out to shoot, bring along your tele lens to experiment with compressing the image.