Throw ratio: the first calculation
Throw ratio is lens-to-screen distance divided by image width.
If a lens covers 1.20-1.70:1, a 1.50:1 requirement is inside the nominal range. That does not yet prove the installation works, because lens shift and projector-specific geometry still have to be checked.
The main types of projection lens
Ultra-short throw
Very low throw ratios, sometimes around 0.3-0.5:1 or lower, for positions extremely close to the screen. Alignment and screen flatness become critical.
Short throw
Useful when the projector must sit closer than a conventional cinema position. Can solve architecture, but often with more demanding shift limits.
Standard zoom
The normal workhorse range. Good balance of installation flexibility, optical performance and available shift.
Long throw
For projection rooms, rear locations or very large spaces. Long optics can place the projector well away from the seating area.
Prime / fixed lens
One throw ratio rather than a zoom range. It can offer excellent optical performance but requires precise projector placement.
Interchangeable zoom
The high-end installation approach: choose one lens family member for the required throw and retain motorized focus/zoom where supported.
Integrated versus interchangeable optics
JVC NZ700/NZ800/NZ900, Sony BRAVIA Projector 7/8/9 and Epson QB1000 use integrated lens systems. The projector model defines the throw range, shift and zoom capability.
Epson QL3000/QL7000, Barco I600, Heimdall, Freya/Freya+ and Nerthus use interchangeable optics. Christie also offers broad speciality-lens ecosystems on its installation/cinema platforms. Interchangeable lenses dramatically increase placement flexibility, but they also make lens selection a formal part of the equipment schedule.
Lens shift is not keystone correction
Optical lens shift physically moves the projected image using the lens system while preserving the rectangular pixel geometry. Keystone or digital geometry correction remaps pixels electronically. Optical shift is therefore normally the preferred tool for a conventional installation.
Shift limits are not always independently available. Maximum horizontal shift may reduce the vertical shift available at the same time, and some extreme lenses have different limits from standard zooms. Final geometry should be checked in the manufacturer's lens calculator or installation manual.
Zoom position can affect brightness and quality
At different zoom positions, the effective aperture and light transmission of a lens can change. A projector at the long end of a zoom can therefore deliver less light than the same projector at wide angle. Edge sharpness, chromatic aberration and focus uniformity can also vary through the zoom range.
When we calculate a high-end system, the real lens and zoom position belong in the light budget - especially on a large acoustically transparent screen.
What makes a high-quality projection lens?
Resolution alone is not enough. A good projection optic has to maintain focus across the full image, control chromatic aberration, minimise flare and internal reflections, preserve contrast and transmit light efficiently. MTF and line-pair performance describe how well fine contrast survives through the lens.
Barco's EN83 is a good example of the level of engineering possible in specialist optics: Barco specifies 20 glass elements, multiple coatings, 92 line pairs/mm optical quality, motorized focus/zoom and indexed position read-back.
Lens memories and CinemaScope
With a 2.39:1 constant-height screen, a projector with motorized zoom, shift and focus can store lens memories: one position for 16:9/1.85 content and another that zooms a scope movie wider. This is elegant, but it changes image area and therefore on-screen brightness.
An anamorphic lens is a different approach. It optically stretches the image so more of the projector's imaging area can be used for scope. The trade-offs are cost, additional glass, geometry, mounting complexity and the need for appropriate video processing.
Examples of lens flexibility across the current site
The right design workflow
Fix the desired image width first. Then identify all realistic projector locations and calculate the required throw ratios. Only after that should you shortlist projector/lens combinations and check shift, physical size, airflow, service access and light output at the chosen zoom.
Standards and manufacturer material.
- Barco EN83 high-resolution lens
- Barco projection optics guide
- JVC DLA-NZ900 optics
- Epson QL7000 product information
Standards, product specifications and firmware can change. Final project specification should always be checked against current manufacturer documentation.