Projector setup guide
Work through it in order: lens and throw distance, then physical alignment on the rigging cage, then blending several projectors into one image.
Lens: throw ratio
Throw ratio is the distance from the lens to the screen divided by the image width. A ratio of 1.5 means the projector sits 1.5 feet back for every foot of screen width.
- Ultra short (under 0.4): wall-mounted or tabletop projectors that sit inches from the screen.
- Short (0.4–1.0): small rooms, or places where people walk in front of the beam.
- Standard (1.0–2.0): most home theaters and classrooms.
- Long (over 2.0): large rooms, with the projector at the back.
Screen size assumes a 16:9 image. Many zoom lenses cover a range, such as 1.4–2.2, which gives you a span of distances rather than one exact spot.
Zoom, shift, and focus
Three lens controls do three different jobs. Zoom sets the image size, shift sets where the image lands, and focus makes it sharp. None of them tilts the projector, so none of them adds keystone.
Light from the lens converges to a focus point. The screen is sharp only when it sits at that point. Otherwise each dot becomes a blur spot.
- Zoom changes the image size at a fixed distance by moving the throw ratio within the lens range, such as 1.4 to 2.2.
- Shift moves the image up, down, left, or right by physically moving the lens, with no tilt and no keystone. It is a percent of image height or width: a 100 in wide image with 30% shift moves 30 in.
- Shift limits: lenses usually allow more up than down (for example 50% up and 20% down) and less sideways than vertical. Vertical and horizontal share the same mechanical travel, so using more of one leaves less of the other.
- Focus puts the sharp plane on the screen. Refocus after you change the distance or zoom.
The model uses a 100 in 16:9 screen, a 1.4–2.2 zoom lens, and a typical shift range of +50%/−20% vertical and ±10% horizontal. Real lenses vary, so check the spec sheet.
Rigging cage: align it physically first
A rigging cage holds the projector on the truss and trims its pitch, yaw, and roll by a few degrees. Each axis has its own screw or knob with a lock, and a limit pin that stops travel inside the useful range. Square the projector to the screen with the cage first. Lens shift and digital correction then only handle what is left.
Why tilt distorts the image
A projector's light spreads out as a cone. Tilt the projector and the screen cuts that cone at an angle, so one edge of the image sits deeper in the cone, where the light has spread wider. That side flares out. Compare tilting with shifting the lens to put the image at the same height.
- What sets the width. The cone's width at any point depends on how deep that point is along the projector's axis, not on how long the ray is.
- Tilt. The screen is no longer square to the axis. The top edge meets it deeper than the bottom edge, so the cone has spread wider there. The same nine pixel rows land farther apart at the top, so each pixel covers more area and looks dimmer.
- Shift. The axis stays square to the screen. Every edge is at the same depth, so the image stays a rectangle, even though the top rays are longer than the bottom rays. It is not free: far off the lens axis the image dims toward that edge, which is why lenses limit shift mechanically.
- Focus. A lens focuses on a flat plane square to its axis. A tilted screen is deeper at one edge, so the top and bottom cannot both be sharp.
The cage trims only a few degrees, so its keystone is small: 5° of pitch changes the width by about 3% from one edge to the other. Drag the tilt higher to see the same physics at larger angles. This view uses the same 100 in screen at a 1.5 throw ratio, with a simple ideal-lens estimate for brightness.
Example: Christie One rigging frame (from Christie's instruction sheet)
- Pitch: loosen the two locking rings on the adjustment screw. Turn it right (clockwise) to tilt the image down, or the other way to tilt it up.
- Yaw: loosen the four adjustment knobs with a 6 mm hex key, adjust, then re-tighten them.
- Roll: turn the adjustment pin clockwise to rotate the image clockwise.
- Limit pin: keep the pin more than 0.5 mm from its plate, then tighten the setscrew on each knob to lock.
Barco lists the same three axes for its G60/G62 frame (roll ±3.8°, pitch +3.2/−3.1°, yaw ±4.4°). I couldn't reach its mechanism details. Christie's sheet shows one pitch screw, while this model gives pitch a ratchet on each side. Real frames vary.
The truss mount is perfectly square. Press Crooked mount to practice squaring a projector that hangs slightly off.
What am I looking at?
3D. The truss pipe and plate stay fixed to the room, and the cage moves the projector under it. Drag to orbit, pinch or scroll to zoom.
Pitch. Left: side view of one ratchet lifting the front of the plate about a rear hinge. Right: rear view of both ratchets. Matching sides tilt the projector. Uneven sides twist it.
Yaw. Top view. The projector plate swings about a center pivot. Four lock knobs ride in curved slots, and the limit pin stops the swing.
Shutters. Each projector has a shutter button above the views. Closing one turns that projector's image and beam off in both the 3D and Screen views, so you can check a single projector on its own. It changes no settings, and the readouts still count the projector.
Converge. In Converge mode every position holds two projectors stacked on one frame, both aiming at the same image. Their colors are complements, so lines that coincide look white, and a mismatch shows red and cyan (or green and magenta, blue and yellow) fringes. The two lenses sit about 10 in apart, so each needs lens shift in the opposite direction to land on the same spot. Stacked light adds, so a converged pair is about twice as bright. Edge blending between stacks works as before, layer by layer.
Several projectors. Every projector shows a slice of the same wide grid, so in the overlap the lines from neighboring projectors should land on top of each other, and where two colors mix they brighten. Doubled lines mean the images disagree. The seam error compares where the same pixel lands from each neighbor.
Roll. Rear view, looking toward the screen. The plate turns about the beam axis. On Christie's One frame, turning the adjustment pin clockwise rotates the image clockwise, and the four base plate screws must be loosened first or the knob can break.
- Level the body first. Hang the projector as level as the truss allows. The cage only trims a few degrees.
- Loosen the lock-downs. Free each lock before you turn its knob. Christie's instructions say to loosen the four base plate screws before a roll or yaw adjustment (the step varies by frame), or the knob can break.
- Work one axis at a time. A workable order: roll until the top edge is level, pitch until top and bottom widths match, then yaw until left and right heights match. Re-check roll at the end.
- Lock down, then refine. Re-tighten every lock, then use lens shift and zoom to place the image, and use digital correction last.
This model pivots at the lens, with zero lens shift and a 100 in screen at a 1.5 throw ratio. Real cages pivot nearer the projector's center, so each turn also moves the image a little. The mechanism drawings are illustrative, with angles exaggerated 4×, and layouts differ by model.
Projection blend: 2 or 3 projectors
Two or three projectors side by side, each image overlapping its neighbor. Software blends the overlap so the seams disappear. The overlap pixels are shared, so the combined canvas is narrower than the images laid end to end. A 3:1 canvas is most often two projectors, not three.
- Two projectors. 16:9 gives 3.56:1 with no overlap (32:9) and about 3.3:1 at 15%. 16:10 gives 3.2:1 and reaches 3:1 at 12.5% overlap. Epson's 3:1 DuoLink setup uses two 1080p projectors with a 600 px (31%) blend.
- Three projectors. Three landscape projectors land between 4:1 and 5:1. A true 3:1 would need more than half of each image to overlap, which is not practical.
- How much overlap. Sources range from about 10% to 25% or more. Video-mapping tools often use less, and hardware blends often use 15% or more.
- Get the cages right first. Epson says to use roll, pitch, and yaw on the mounts to minimize electronic adjustment, since point correction only moves each point by up to 32 px.
Each image size is the diagonal of one projector's image. The total screen width and height come from those images and the overlap.