Throw Distance: Is the distance the projector needs to be away from the screen surface “Not the wall”. You need to know how large you want your screen to be so picking a number and sticking with it always best practice. It is important to make this decision before ever looking at projectors as you will only waste your time if you don’t. Most projectors have a zoom feature so your throw distance will be a range “lets say 9 feet to 12 feet for example” This means the front of the glass lens on the projector needs to be a minimum of 9 feet away to a maximum of 12 feet to fill the desired size screen you’ve selected. This range will change drastically with different screen sizes and every projector will be completely different. It is very important that you remember that the placement of the projector is always from the center of the glass lens regardless of the shape / size of the projector as a whole. The throw distance for every projector will be different so finding one that suites your needs can be tricky depending on how small the room is. The bigger the room the more flexibility you will have with your selection.
Vertical Offset: A lot of projectors are designed to sit on a flat table and not hang from the ceiling. You can still mount these projectors on the ceiling but there are a couple of things to be aware of. With these projectors the bottom of the screen is usually higher then the table. These projectors have an offset of more then 100%. Look at the images below to get an idea of what vertical offset is. If you do end up getting a projector with vertical offset you may run into trouble because the image may shoot downwards too far when mounted to the ceiling. You may be forced to build the projector into the ceiling, lower the height of you screen too low or use a smaller screen altogether. It’s usually safest to get a projector that has exactly 100% vertical offset in a residential setting unless you really know what you are doing. If you get a projector with 100% vertical offset all you need to do is make sure your projector is mounted so that center of the projectors glass lens is the same height as the top of your screens white projection surface. Once again see picture below to get a better idea of what I mean. The image on the bottom shows a projector with more then 100% offset.
Horizontal Lens Offset: Projectors aren’t always square in shape and don’t always have the glass lens in the center of the casing. Most of the time a projector is rectangular in shape with the lens off to one side. Make sure you offset your projector mount so that the center of the projectors glass lens lines up with the center of your screen. If you don’t take this into consideration you might mount the projector too far to the right and end up needing to rotate the projector on the mount to aim it left. Your geometry is now way of because the lens isn’t perpendicular to the center of the screen and you will have a very bad keystone “Read Keystone”. The same thing will happen if it is mounted too low or too high.
Lens Shift - Vertical & Horizontal: If the projector you chose just so happens to have this really nice feature you might save yourself some headache. Lens Shift physically moves the whole image left, right, up or down. Some projectors only have one of the two types of lens shit while others have both. Most projectors never come with this feature and you usually pay a premium for it. Let’s say you’ve mounted your projector to high or maybe too far to the right. With lens shift you can simply turn the dial and shift the entire image down or left without having to worry about the image being keystoned. If you want your projector to be right up against the ceiling but want your screen to be lower this becomes a very useful feature. In this case you could use a projector with some vertical offset that shoots the image on a slight downward angle but be cautious with this and make sure you triple check your measurements before actually buying or mounting the projector. If you are looking at a projector with lens shift capabilities make sure you find out how many inches of movement you will get to have an idea of where the screen will need to be.
Keystone: Is what will happen if your projection geometry is off in any way. The image will not be square and will not fit the screen properly. Most projectors come with a keystone correction setting in the menu. This doesn’t solve the problem and the projector is simply processing the image and reformatting it to look square. You will end up loosing some detail because some of the dots “Pixels” are not being used. Make sure to follow the information above and you should be able to avoid this unpleasant experience.
