Knowledge Base
The relationship between the image width and height
The aspect ratio is a term which describes the shape of rectangle. It is normally expressed in terms of how many times (the ratio) the height of the rectangle fits into the width of the rectangle.
For example a rectangle where the width is 2.4 times greater than the height would be said to have an aspect ratio of 2.40:1
In video systems several different aspect ratios may need to be considered at the same time:
The aspect ratio of the screen
The aspect ratio of the projector
The aspect ratio of the content being displayed
There is every chance that these aspect ratios are different from each other. Handling this variance correctly is a key challenge in cinema design.
The correction factor to be applied to the projector brightness based on the zoom.
The brightness factor is a way of describing how the brightness changes as a zoom lens moves from the shortest to the longest zoom. In a zoom lens, the brightness is highest at the shortest zoom and lowest at longest zoom.
Projector brightness specifications are normally measured with the lens at medium zoom. This means that at medium zoom, the brightness factor is 1. As you move towards the shorter end on the zoom, the brightness increases so you have a brightness factor greater than 1. As you move towards the longer end of the zoom the brightness decreases so you have a brightness factor less than 1.
The brightness factor is directly driven by the F-Stop range of the lens. The closer the F-Stop values at each end of the lens, the lower the rate of change of the brightness factor.
When the projector is located on the audience side of the screen.
Front Projection is a setup where a projector is positioned on the same side of the screen as the audience. This is the most common and standard way to set up a home theater or a conference room with a projector. The projector sends light through its lens to the screen, and the image is reflected back towards the viewers. This setup is generally straightforward to install and offers the best performance for many applications.
For optimal results, care should be taken to ensure the room is dark enough and that there is no light source between the projector and the screen, as this can wash out the image. The audience also needs to be positioned so that their shadows do not fall on the screen.
The fixed position difference between the image at the lens and at the screen.
Lens offset refers to a fixed difference between the image’s centre point at the lens and its position on the screen. This is a crucial concept to understand when mounting a projector, especially if you are not placing it directly in line with the centre of the screen.
For example, a projector might have a lens offset that positions the bottom of the image higher than the lens itself. This allows for ceiling mounting without needing to tilt the projector, which can cause image distortion. Lens offset is a static value, determined by the projector’s design, and is a key factor in calculating the correct installation height and location.
The variable position difference between the image at the lens and at the screen.
Lens shift is the ability to physically move the projector’s lens to adjust the position of the image on the screen without moving the projector itself or resorting to digital keystone correction. Unlike fixed lens offset, lens shift is a variable feature that allows for more flexibility during installation. You can shift the image horizontally and/or vertically to precisely centre it on the screen.
This feature is particularly useful when the projector cannot be placed in a perfect alignment with the screen due to obstacles or room layout. Using lens shift maintains the image’s quality and aspect ratio, unlike digital keystone correction, which distorts the image by compressing or stretching pixels.
The aspect of the projectors imaging device.
The Native Image Aspect is the fixed aspect ratio of a projector’s imaging device, such as a DLP chip, LCD panel, or LCoS panel. This ratio represents the physical shape of the image-forming chip inside the projector. For example, a projector with a native aspect of 16:9 has a chip with a width-to-height ratio of 16 to 9.
Projectors are designed to display content at this native aspect ratio without any scaling or cropping, which ensures the highest image quality. While a projector can display content with different aspect ratios (e.g., a 4:3 image on a 16:9 projector), it will do so by adding black bars to fill the screen or by digitally scaling the image, which can result in a loss of sharpness and detail.
The orientation of the projector compared to the image on screen.
Projection orientation describes the way a projector is positioned relative to the screen. The most common orientations are table-top, ceiling-mounted, front, and rear.
Table-top orientation is used when the projector is placed on a flat surface, like a table, in front of the screen.
Ceiling-mounted orientation is when the projector is fixed to the ceiling, usually upside-down, to get it out of the way of the audience and to provide a clean setup.
Front projection is when the projector and the audience are on the same side of the screen.
Rear projection is when the projector is placed behind a translucent screen, projecting the image forward for the audience to see from the other side. The correct orientation setting must be selected in the projector’s menu to ensure the image is not displayed upside down or flipped.
The distance between the screen and the projector.
Throw distance is the measurement from the projector’s lens to the projection screen. This is a critical factor in any projector setup as it determines the size of the image that can be created. The throw distance, combined with the projector’s lens type (e.g., standard, short-throw, or ultra-short-throw), dictates where the projector needs to be placed to achieve a desired screen size.
For example, a short-throw projector can produce a large image from a very short distance, making it ideal for smaller rooms or where space is limited. Conversely, a long throw distance is required for a large venue or when the projector needs to be placed far from the screen.
The distance between the screen and projector in number of screen widths.
Throw ratio is a specification that relates the throw distance of a projector to the width of the projected image. It is calculated by dividing the throw distance by the screen width (Throw Ratio = Throw Distance / Screen Width). This number is essential for installers because it allows them to calculate the exact distance a projector must be placed to achieve a specific screen size.
For example, a projector with a throw ratio of 1.5:1 means that for every foot of screen width, the projector needs to be placed 1.5 feet away. A lower throw ratio indicates a shorter distance needed for the same screen size, while a higher ratio indicates a longer distance.