The Vital Role Depth of Field Plays in Creating a Successful Flight Simulator

When building a successful flight simulator, the end goal is to provide the pilot with visuals that mirror what they would encounter in a real-world situation, including the ability to recreate accurate perspectives and sight lines, all in order to fully immerse them in the scenario they are rehearsing. To accomplish this, recent simulators have not only implemented components such as curved screens, but have also sought to push the limits of the screen’s curvature.

What this entails for designers when they consider the projectors to use in such simulators (e.g., projectors that support projection on curved screens), is that they will need to think beyond the specs which most are familiar with when purchasing a projector, such as brightness, colour performance, resolution, and so on. Designers will need to also take into account aspects related to the space that the simulator will occupy including room size, the overall number of screens, installation location and position (height, angle, etc.), since these factors influence the effectiveness of the edge-blending process. In the midst of all these factors, one projector spec plays an outsized role in the level of success for the entire endeavour, as it is the one factor that determines from the outset whether the images projected on a dome-screen are clear enough to fully engage the pilot during their training: Depth of Field (DOF).

Depth of field refers to the distance between the nearest point in front of and the farthest point behind the projector’s focal plane where it can still produce an image that is considered in focus. To flip this definition around, all images produced by a projector within its DOF can be seen clearly by the viewer, while all images outside of it will appear blurry.

As seen in the image below, when a flight simulator uses a dome-screen, the screen will feature curvature along both the HFOV (Horizontal Field of View) and the VFOV (Vertical Field of View), which produces a concavity that the projector and its image has to deal with since the focus point will be different for each point along the screen. So as one moves from the outer edges of the projected image inwards, the screen moves farther away from the lens, producing the “depth” which a projector’s DOF has to incorporate. This is especially true for screens with a higher level of curvature. 

This idea can be more easily grasped using the following demonstration where a room featuring a screen with a 220-degree HFOV and 40-degree VFOV and three LU951ST short-throw projectors from BenQ’s Installation series of projectors is undergoing the edge-blending process. In this type of situation, calculating the most ideal DOF becomes a crucial step in the design process.

In this setup the middle projector projects a grid with a laser spirit level positioned in the center. Once the spirit level’s height is adjusted so that it is level with the center of the screen’s curvature, the spirit level is moved backwards until its horizontal line covers the distance between left and right edges of the grid. Then, as seen in the image below, the projector switches to a word pattern to check if the image is focused in all areas, including at the corners. At this point placing a laser range finder atop the laser spirit level allows you to calculate the depth of field, which as seen in the final image is essentially 0.8 m. So, in effect, if you want to project a fully focused image on a screen with a 220-degree HFOV, your projector should have a depth of field value of at least 0.8 m.