Why you need to know these terms
These terms are what I consider the most important for someone just starting to pick up projections for the first time. These will help you understand the basics of what you need to know which I talk about in my other article here.
If you have other terms you would like added to this list, please reach out on our contact page to let us know! Without further ado, here are the terms:
Aspect Ratio
The Aspect ratio is the relative Width and Height of an image separated by a colon (:). To Calculate the aspect ratio for a projection surface on stage, measure the width and height and simplify the fraction as much as possible. You can also use an online calculator.
I use, aspectratiocalculator.com but there are many options if you search for one when you need it. This gives you the simplest form of the aspect ratio which make it easy to create content out of. In theatre this number tends to be a bit funky since we all design for looks first, not aspect ratio first.
Brightness
Projector brightness is measured in lumens (lm) and the higher the lumen count, the brighter the image will be. Because Lumens are hard to measure without complex tools, You need to use a few assumptions to figure out what fits your needs best.
I recommend the following based off screens measured diagonally from one corner to the other:
- Up to 120 Inches: 5,000-8,000 lumens
- 120-220 Inches: 8,000-12,000 lumens
- 220-300 Inches: 12,000-15,000
- 300 Inches or more: More than 15,000 lumens
If you are projecting on surfaces much larger than 300 inches, you should consider using multiple projectors. These can either overlap completely to double the projection power, or be blended together as one seamless image with each projector covering part of the surface.
Edge Blending
When using two or more projectors with each covering only part of the surface, the two images must be blended together to create a seamless image. This feature might be available in the projection software you use, or in the projectors themselves.
As you can see in the example below, each projector fades out evenly as it crosses over into the other projectors throw. This creates one solid image using two projectors, which doubles the resolution and increases brightness.
Four Corner Correction
This form of geometric image correction lets you control each of the four corners of the image individually. This lets you fine tune the exact placement of the images edge, and automatically reshapes the image to look flat on the surface.
Front Projection
Front projection is done on a solid projection screen which is meant to reflect the light back towards the audience. This is what you typically think of in the movie theater. This option is typically less expensive, but in live theatre the actors often interfere with the beam of light.
HDMI
The standard connection used for short runs of less than 30-40 feet (10-12 meters). These cables are relatively common, and relatively inexpensive. They have maximum length limits of about 45 feet before signal degradation is likely, so aren’t ideal for long distances often found in theatre.
HDBaseT
Used to extend HDMI signal using CAT5 cables, the protocol has a length limit of 328 feet (100 meters). Most high end projectors have an HDBaseT input, but most computers require a separate device to convert the HDMI signal. Convertors are usually under $100.
Keystone Correction
This image correction tool is the fastest way to make major changes when the image does not appear flat on the projection surface. It works by expanding or squeezing the image so it appears flat on an angled surface. It is named after the famous “keystone” that holds stone arch bridges together.
Often used as the first step in getting the projection image in the right general position, it has both horizontal and vertical keystone adjustments on most projectors.
Throw Ratio
This is used to calculate the distance from the projection surface to mount the projector. Multiply the desired image width by the Throw Ratio to calculate how far away to mount the projector. For example with a throw ratio of 2 with a desired image size of 10 feet across, the projector would need to be 20 feet away.
To find Throw Ratio, use the following formula:
Throw Distance (Feet) / Image Width (Feet) = Throw Ratio
To find Throw Distance, use the following formula:
Image Width (feet) x Throw Ratio = Throw Distance (feet)
To calculate Image Width, use:
Throw Distance (feet) / Throw Ratio = Image Width (feet)
You can use any unit of measure you would like, just know that both measurements must be the same unit of measure.
Lenses
Larger high end projectors often have swappable lenses which offer different throw ratios. These different lenses allow the projector to be used in more situations. These are especially helpful in spaces where the projectors will be moved often.
Image Shift
Image Shifting is a function which allows fine adjustments of the image location to be made within the projector lens. It gives users the ability to remotely to control the image, shifting it up and down, or left and right. This is much faster than moving the projector itself for each adjustment.
Lumens
Lumens are a measure of the brightness of a projector. Based on the intended size of the image, more or less brightness is required. For theatrical and stage uses, you should almost always choose the highest lumen output your budget will support.
Playback Software
Playback software is the software used to control the media played through the projectors. Though there are some basic software options, many of the more advanced software is capable of much more than simply playing back video.
Projection Mapping
Projection Mapping is the practice of using computer programs to manipulate a projection image to fit an object. Mapping software is commonly used to make a 3d object appear fully wrapped in a projection.
Rear Projection
Rear Projection is when the projectors are mounted behind the projection surface rather than in front. This is especially helpful in theatrical settings where the performers would interfere with the projection image if it came from the front side of the screen.
Short Throw Lens/Projector
Short Throw Projectors and Lenses are used to mount the projector extremely close to the projection surface. These are extremely helpful when space is at a premium in smaller spaces.
Zoom
The Zoom feature of a projector is as it sounds, the ability to expand or shrink the image as necessary. This helps to perfectly fit the projected image to the exact size needed for each situation.
