Or: “What is throw distance?” “What is throw ratio?”
I was setting up for an internal hotel staff event and the sales manager came in: “Can you push the screen back? We need room for the dessert station.” The screen was set up for rear projection and unfortunately I needed at least 10 feet between the screen and projector, so the dessert station had to find a new home. The good news is it was a low stakes internal event and we had some flexibility. But you don’t want any surprises for your event. How do you plan to have the right amount of space?In an ideal world, your AV partner will tell you how much room is needed, or give you a diagram. But it’s good to have a rough idea yourself. Generally speaking the bigger the screen the farther away the projector will need to be. But even with the same screen some projectors can be placed closer than others.
The numbers you’ll need are the width of your screen, and the projector’s “throw ratio”. Multiply one by the other to get the distance between projector and screen. For example, if you have a screen that’s 10 feet wide, and a projector with a throw ratio of .8, then you’ll need .8 feet from screen to projector. (10’x.8=.8′) If you have a screen that’s 6 feet wide and a projector with a 1.5 throw ratio you’ll need to plan to use 9 feet. (6’x1.5=9′)
This measurement is from the lens of the projector, so you’ll want to pad at least a little bit to account for the projector body and cart/stand. The distance from the projector lens to the screen is called the “throw distance”. Because the two concepts are dependent on each other some folks will use it interchangeably with “throw ratio.” If you can’t find the throw ratio on the proposal, a (very!) rough rule of thumb is rear projection typically uses a .8 lens and front projection might be between a 1.2 and 2 throw ratio.