# Converting Diagonal Field of View (FOV) to Horizontal FOV As is commonly done with cameras, DJI advertises the Field of View (FOV) of their lenses using the diagonal angle. This FOV value corresponds to an aspect ratio of 4x3 which is typically used for photos.

It is sometimes desired to know either the horizontal FOV or vertical FOV or both. To compute either the horizontal or vertical FOV, it is tempting to use the Pythagorean Theorem to compute the ratio of aspect-horizontal to aspect-diagonal and then multiply the diagonal FOV by that ratio to obtain the horizontal FOV but that would be incorrect. This method is summarized in the figure to the right.

The reason the above method would be incorrect is because the FOV angle, when projected onto a flat plane has a non-linear relationship with distances along that plane. For example, a one-degree change of FOV when the FOV is small results in a relatively small linear change on that flat plane. However, a one-degree change of FOV when the FOV is large (closer to 180) yields a massive change on that same flat plane.