Do you need a beam-splitter teleprompter?

What the glass actually does

A beam splitter is a pane of partly reflective glass set at an angle in front of the lens. The camera looks straight through it. You look at it and see the reflection of a screen lying below. Because the text and the lens are on the same line, reading the text means looking down the lens. There is no gap between the two, so there is no angle for the viewer to notice.

That solves one problem completely: gaze offset, your eyes pointing at a spot that is not the camera. It does nothing for the other two problems that make reading look like reading. Wide lines still make your eyes sweep. A scroll running on a timer still makes you glance ahead and back to check where you are. I went through all three in stop losing eye contact while reading a script, and the short version is that glass fixes the geometry and leaves the rest to you and your software.

So the real question is not whether glass works. It does. The question is whether gaze offset is your biggest problem, and whether something cheaper would fix it just as well in your room.

When the glass earns its place

What a viewer reads as "not looking at me" is the angle between the lens and the words. That angle depends on two things: how far the text is from the lens, and how far you are from both. Close to the camera, a small gap is a big angle. Far away, the same gap disappears.

Glass is worth buying when that angle cannot be made small any other way:

• You have to sit close. A small room, a desk you cannot leave, a tight frame you cannot get by cropping. At a metre or less, even a screen right under the lens shows as a downward look. Glass removes it.
• You look straight at the viewer for long stretches. Direct-address videos, courses, a message to camera where any tilt reads as distraction. The longer the take, the more a constant offset is noticed.
• You film with a camera that a rig can mount on. A beam splitter sits in front of a real lens, with a hood that blocks the light around it. A camera on a tripod or a rail fits that. A webcam clipped to a monitor mostly does not.
• The setup stays put. Glass rewards a corner that is built once and left alone. Aligning the rig, the hood and the screen every session costs more time than the eye contact gives back.

When it is money wasted

The same list read the other way tells you when to keep your money.

• You can sit back. If the room lets you sit a couple of metres from the camera and crop in, the angle from a screen under the lens is already too small to see. Glass would fix a problem the distance has already fixed.
• Your camera is in your laptop lid. The camera has to sit behind the glass. A built-in webcam is not going behind anything, and propping a laptop up behind a rig puts the screen you work on out of reach.
• You move. Walking, gesturing at a whiteboard, turning to a product on the table. Glass gives you one narrow sweet spot straight in front of it, and you leave it the moment you move.
• You have not fixed the other two problems. If your column is wide and your scroll runs on a clock, the glass puts your darting eyes exactly on the lens, where the viewer sees them best. Narrow the column and sort the pace first.
• Your room is bright. Partly reflective glass lets less light through to the lens than none at all, and a bright window behind you can show up in it. Neither is a reason to avoid glass, but both are a reason to try it before you build a set around it.

The screen under the lens

The option most people skip is the boring one: a small monitor, or the bottom of a screen you already have, placed directly under the camera and raised until the reading line almost touches the lens. No glass, no hood, no mirrored text.

It leaves a small, steady downward look. At a desk that look is visible but reads as thinking, and the further back you sit, the less of it there is. It is also the setup you can change in a minute, which matters if you film in more than one place. I wrote about making the most of it at close range in a small prompter, right under your camera.

A good test before buying anything: put the text under the lens, sit where you will record, film a minute and watch it back with the sound off. If you cannot see your eyes leaving the camera, the glass will not buy you much. If you can, and you cannot sit further back, that is the setup glass was made for.

What the software must do either way

Whichever you choose, the prompter app has a few jobs that do not change.

Flip the text for glass. A beam splitter shows you a reflection of the screen, and a reflection reverses the text. The software has to flip it back so it reads normally in the glass. In Mirrento this is Mirror (for beam splitter) in Settings, Display. It flips the text left to right and stays set from one session to the next. Turn it off if you move back to a screen under the lens, or every line will read backwards.

Open on the right screen, full screen. The screen in a glass rig, or the small monitor under the lens, is a second display. The prompter should fill it without you dragging a window across the room. Mirrento opens the prompter full screen on an external display your Mac sees, and if you have several, Show on Display lets you pick one and remembers it. With no second screen, it offers to open the prompter in a window on the screen you have instead. The details are in open the prompter on the right screen, every time.

Put the reading line where the lens is. On glass, the line you read should sit where the lens is behind it. Under the lens, it should be at the top edge of the screen, nearest the camera. An eye line setting that moves the reading line up or down handles both, and margins narrow the column so your eyes do not sweep.

Stop making you check the scroll. This is the part glass cannot do. A clock-driven scroll keeps you monitoring your position, and every check is an eye movement right on the lens. A scroll that follows your voice removes the reason to check. That is what Mirrento's Voice follow does, and what speed a teleprompter should scroll at explains why no fixed speed gets you there.

If you are about to order glass, the 7-day trial is enough to run the test above on a screen you already own, with the text following your voice, and see how much of the problem is left before you spend on hardware.