Screens and projection · SERVICE · REV 2026-10-06
Projectors
A projector is geometry first: where the lens sits, what the image width is, and what light falls on the screen from the room rather than from the projector. Throw ratio is a class name. The lens table at the shift in use is the width. A shadow in short throw is a position error, not a lamp defect.
Definition
Throw ratio = projector-to-screen distance ÷ image width. A number like a lens class does not replace that lens’s table: vertical and horizontal shift change width and place. Ambient light lifts the black floor, so a brighter projector in a lit room does not restore black. Screen gain is a figure from the screen sheet, usually a peak on axis, and it falls off axis. This page gives neither a gain nor a lumen figure.
Lamp and laser are a maintenance choice: a lamp has a stated life on the sheet, a replacement, and a cost; laser moves maintenance to cooling, filters, and the source warranty, with gradual decline rather than necessarily a sudden failure. Short throw puts the lens near the screen, so a presenter walks through the cone and casts a shadow. AVIXA DISCAS is a procedure that ties image height to the farthest viewer and the content class. This page does not perform the procedure and does not output a screen height.
When is this service needed?
Distance exists and light is controlled
A hall that can be dimmed, with a screen far enough for a reasonable lens. Projection is a fit tool here.
Short throw is forced
The projector is close to the screen. Shadow and shift are drawn before the lens is bought, not after.
Maintenance away from periodic replacement
Long daily use may favour laser as a maintenance schedule. Not because the word is newer.
When a self-lit screen is more honest
Windows that will not be covered, or a bright stand. More lumens do not build black. See the LED page.
Where it is used
Lecture halls
A screen behind the talker. A ceiling throw has to clear the head and the shadow on the picture.
Cinema and screening rooms
Darkness is part of the design. Gain and lens serve the end seat, not only mid-row.
Multipurpose halls
House light sometimes stays on. Contrast is discussed for the lit condition, not for a laboratory room.
Booths and exhibitions
Booth depth may not allow the throw. A short lens glares the aisle if it is aimed badly.
Parts of the solution
The lens and its table
Throw ratio is a range, not a magic number. Width is read at the actual distance and shift.
The screen
Gain, viewing angle, and material. High gain narrows the good seat and can make a hot spot.
Source and ambient light
Sheet lumens in the stated lamp mode are compared with light falling on the screen from the hall. This page gives no lumen figure.
Mount and ceiling
Stiffness, a cable route, and a service opening for the lamp or filter without demolishing the ceiling.
Image processing
Shift, limited geometry correction, and delay against sound. Heavy geometry correction spends sharpness and does not fix a badly skewed wall.
Engineering considerations
Throw ratio is not the table
Distance over width is a class. The lens table at the shift is the design.
Contrast is a room
Light on the screen from windows and spotlights lifts black. The projector does not cancel that alone.
Gain is not free brightness
The peak is on axis. The end seat loses it. The sheet has the curve, not only the word gain.
Short-throw shadow
The cone is wide near the screen. A presenter inside it is a shadow on the picture. Place the lens above heads or outside the walk.
DISCAS is not performed here
The standard ties image height to distance and task. This page does not output a height.
Materials
The screen surface
Gain and look come from the screen sheet for that build. White wall paint is not a screen of known gain.
The light source
A replaceable lamp or a laser source, according to the life and maintenance sheet. The choice is a schedule, not a slogan.
The hanging structure
The projector’s weight and its vibration. The ceiling fixing is reviewed structurally. This page gives no weight.
Related systems
Hall blackout
Curtains, windows, and house light. Without blackout, contrast is a losing decision whatever the projector.
Picture sound
Lip delay against sound is checked. A projector is not necessarily instant.
LED as an alternative
When light cannot be controlled or throw does not exist. The comparison is on the screen page.
Sightline
The bottom of the screen may be hidden by the front row. Image height is a seating decision, not only a lens decision.
Design sequence
- 01
Fix the screen position from the sightline before choosing the lens.
- 02
Measure the distance available for the lens, then read the lens table at the shift, not the throw ratio alone.
- 03
Estimate hall light on the screen in the real operating mode. Do not assume a darkness that will not happen.
- 04
Choose lamp or laser from operating hours, replacement, and cooling, and write that into maintenance.
- 05
If image size must come from the standard, run AVIXA DISCAS as a procedure, not as a guess from this page.
Delivery sequence
- 01
The mount is installed so the lamp or filter service opening stays possible.
- 02
Shift is set on the lens before digital correction is used. Heavy correction is the last tool.
- 03
The shadow zone in short throw is marked and the presenter’s movement is kept outside it.
- 04
Curtains and house light are tied to show mode, not left to random manual use.
- 05
The lens table and the distance are recorded in the handover file. A lens change restarts the calculation.
Testing
Actual image width
Measured on the screen at the shift in use and compared with the table. The ratio alone is not accepted.
Contrast in hall mode
With operating light, not only in test darkness. A lifted black is recorded.
The end seat
Screen gain is viewed from the end. A hot spot in the centre is a defect if the end is dead.
Commissioning
The light mode is documented
Which curtain closes and which spotlight turns off. Handover without that mode cannot be repeated.
The named maintenance
Lamp hours or laser conditions from the sheet, and a spare if it is a lamp. No slogan on this page.
No DISCAS height here
If the standard is used, the result comes from the project calculation, not from this page.
Maintenance
Lamp replacement
According to the sheet’s curve, not after the show has already failed. Stock is part of operation.
Laser filter and cooling
Blockage cuts light and life. Maintenance is a schedule, not the sentence “maintenance free”.
Screen and lens cleaning
By the allowed method. A scratched screen changes gain locally.
Common mistakes
Buying on lumens alone
A lit room lifts black. A stronger projector washes the picture and does not build contrast.
A throw ratio with no table
The class does not give width at the shift. The picture may grow or leave the screen.
Short throw in the walkway
The presenter is a permanent shadow. The geometry was available before installation.
Laser as a slogan
Choosing the source because the word is newer, with no hours, no cooling, and no warranty. Maintenance is the question.
Short comparison
The comparison is a way to choose a path. It is not a product recommendation and it is not a code.
| Path | Fits when | Weakens when |
|---|---|---|
| A standard lens | Distance allows the image width without extreme shift and without people walking in the cone. | When distance is short, so the image grows past the screen or the projector collides with the audience. |
| Short throw | There is no depth, and the shadow is planned so nobody stands in the cone. | When the presenter stands in front of the screen. The shadow becomes part of the picture. |
| LED instead of projection | Ambient light is high or there is no throw distance. | When the hall can go dark and the distance is enough. Projection may be simpler thermally and easier to service. |
Discussion ranges
Any number here is a preliminary discussion range from practice or a named reference. Replace it with the project criterion, laboratory data, and on-site measurement.
| Item | What is discussed | Limit of this page |
|---|---|---|
| Throw ratio | Lens-to-screen distance divided by image width. A class name for the lens. | It is not the image width. The table at the real shift and distance replaces it. No ready-made ratio on this page. |
| Screen gain | A peak from the screen sheet, usually on axis, with a curve that falls toward the sides. | No gain is assigned by this page. A figure without a viewing curve does not describe the end seat. |
| Lamp life or laser decline | Hours or a curve from the source sheet at the named operating mode. | Not image quality and not a superiority slogan. A maintenance figure only. No hours are invented here. |
| Image height per DISCAS | The result of the AVIXA procedure from the farthest viewer and the content class, when the standard is required. | This page does not perform the procedure and does not output a height. Copying a figure from another project is not the standard. |
What this page does not claim
No fire classification, absorption coefficient, sound pressure level, or legal capacity on this page may be copied into a quotation. Those values come from a product test report, a measurement, or the local code adopted for the project.
Questions designers and owners ask
Is throw ratio enough to choose the lens?
No. It is distance over width. The lens table at the shift gives the actual width. Without it the picture can leave the screen.
Why is the picture washed out if the projector is powerful?
Hall light on the screen lifts black. Contrast is blackout and gain, not lumens alone. This page gives no lumen figure.
Does laser remove maintenance?
No. It moves part of it from lamp replacement to cooling, filters, and warranty terms. Read the sheet.
The presenter blocks the picture. What now?
Short throw puts the cone through the body. Raise the projector or move the walk out of the cone. A brighter unit does not remove the shadow.
Do you calculate screen size with DISCAS?
No. The standard exists and ties height to distance and task. This page does not perform the calculation.
Technical sources
- The manufacturer lens table
Width at distance and shift. Throw ratio does not replace it, and this page publishes no table.
- AVIXA DISCAS
The procedure for 2D content image size. This page does not perform it and does not output a screen height.
- The screen sheet and the light-source sheet
Gain and the viewing curve, and lamp hours or laser decline. No figures from this page.
Last editorial review: 2026-10-06. Review means the text was checked, not that a project was measured.
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