Triangular composition looks to add sharp angles into the image. While a photographer could simply capture images of triangles, it is more interesting to incorporate them in the composition. In this image, we can see that the park entrance sign was captured so that it crossed the frame at angle, creating various geometric shapes along the way. The fluffy and irregular clouds in the background provide nice contrast as well.
Nikon Z6III | Nikkor Z 50mm f/1.8
f/9.0 | 1/4000 | 50mm | ISO 100
