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So, I don't know how widely known this is, but my friend Destin from SmarterEveryDay. he is not a fan of teleprompters. Not for himself, and he doesn't like it when other people use them, either. Something about it just isn't as authentic, and you can often see the person's eyes flicking back and forth and back and forth in an unnatural way as they read the text. Well, Destin, some people just aren't as naturally charismatic as you are. this video's for the rest of us. Here's the thing about teleprompters - those tricks of physics where a carefully placed
partially transmissive mirror allows you to look straight into the camera lens while simultaneously reading a script off of a screen - if you put one close to you so you can read the text more easily, then your eyes are visibly moving back and forth and it's pretty obvious that you're reading. So you put it far away, but then it's too small to read. There must be some ideal teleprompter distance and size, right? Yes. It's this equation. But we're getting ahead of ourselves. I should also add that I'm definitely not an experienced teleprompter user and there are plenty of better guides out there for how to actually perform with a prompter without seeming awkward and unnatural - there's more
to it than just getting the distance right. But this video is purely about that - the physics of the eye motion and the best distance. What actually matters for teleprompter eye motion is the experience of the viewer - when they are looking at their screen, how much do your eyes move in their field of view. Move too much (in their perspective) and they might notice. The factors that affect the teleprompter paradox are these: 1) What's the radius of your eyeball? This combined with the rotation of your eyes determines how far your irises actually move side to side 2) How far away are you from the teleprompter?
Farther away and your eyes will have to rotate less to look at the sides of the text 3) How wide is the text you're reading? The narrower it is, the less your eyes will have to move from side to side 4) How wide is the camera field of view relative to the motion of your eyes? The wider the view, the smaller your eyes will appear and the less (proportionally) your eyes will move side to side across the screen 5) How big is the screen that you're being watched on? The bigger it is, the bigger your eyes and eye movements will appear to the person watching you and 6) How far is the viewer from their screen? The farther away they are, the smaller you'll appear and the harder it'll be for them to notice your eyes moving
When you combine these six factors together using basic trigonometry, you end up with what I'll call the "teleprompter equation". It's busy, but not all of it is within your control. Like, you can't change the radius of your eye - it's probably about a centimeter and will stay that way. And you can't control what size screen people are using when they watch your video, nor how far they sit from it. But we can simplify that part anyway, because people tend to sit closer to little screens and farther from big screens, meaning the ratio of those distances (which is in the equation), stays roughly the same.
But the question still remains: when your eyes move back and forth, how small should the angle they make be from the viewer's perspective? Here's where physics really comes into the picture: Light is a wave, and waves spread out and diffract when they pass through openings, becoming blurred. So human eyes - with their pupils - have limits to their resolving power; typical good human eyes can't distinguish features that are smaller than about a 60th of a degree, or movements that are about half that size. So if the motion of your eyes,
as seen by a viewer, is less than around a 60th of a degree, they probably won't notice, and if it's less than a 120th of a degree, it's essentially physically impossible for them to notice. But that's probably overkill. So. We want the "teleprompter equation" to be at most around a 60th of a degree. Rearranging the equation allows us to come to a conveniently simple answer: the distance from the host to the screen should be at least 30 times the width of the prompter divided by the size of the camera's view, all measured in meters. For feet, it's 100 times the width of the prompter divided by the field of view.
For example, for 30cm wide teleprompter text and a field of view that's around 2m wide (that is, your hands would be just about out of frame), the camera should be at least 4.5m away. Well, technically the teleprompter should be 4.5 meters away, so the camera will have to be just a touch farther. If you zoom in so the frame is now only 1m wide, then the teleprompter should be at least 9 meters away! For a small phone teleprompter, that same 1 meter frame can have the camera closer - "only" 3.6 meters away. The problem, of course, is that it's really hard to read text on a 12cm phone 3.6 meters away. And this is the true essence of the teleprompter paradox. In order for
the viewers to not be able to notice you're reading from a teleprompter, the teleprompter might have to be so far away you can't read it! The only real solutions are to zoom out so the presenter is smaller in the frame (like, with a 2 meter frame it's fine to have a phone-sized teleprompter just 1.8 meters away), or you need to be ok with sharp-eyed viewers being able to notice your eyes moving, or you should use an ear prompter (where the script is read out loud into an earpiece in your ear, rather than put on a screen, and you just say out loud what you're hearing). It boils down to this: to avoid detectable eye
motion when using a teleprompter (and therefore to avoid judgement by Destin). Get farther away, make your text narrower, or zoom your camera out (though zooming out too much can cause the edge of the teleprompter to appear in view). But don't get farther away and simultaneously make the teleprompter bigger. that defeats the purpose.
