Two of the more common problems that prospective owners of projector-based home theaters encounter are:
1. not having an understanding how go about selecting a projector and screen combination that will integrate well into their ‘home theater’ room; and
2. they find that after mounting the screen and the projector they do not fully understand how to mechanically and optically align the projector in order to achieve a projected image that is a perfect, or near perfect, rectangle correctly centered on the screen.
I will cover the above topics in two parts by covering the first item in this blog and continuing in Part 2 (next month) with a discussion that will address the second item.
The Projector, Screen and Room as a System
When choosing a projector and a screen their capabilities and characteristics need to not only complement each other but also integrate well in the environment of your ‘home theater’ room. When setting up a new home theater (HT), either in a room dedicated for that purpose or within a more general living space, you need to decide on the layout of the HT room including the seating locations, the locations of external light sources (e.g., windows), the locations of interior light sources, the desired position of the screen and the available locations for mounting the projector in front of the desired screen position.
Before getting into the specifics related to projectors and screens, there are some general concepts/rules, discussed below, that should be considered when converting a room into a HT. Note that I am limiting my discussion to only video-related considerations, while recognizing there are also many audio considerations, such as where to place the speakers, when setting up the HT.
1. Front projection is intended to work in a dark environment. Think movie theater dark, or even darker, for the best results. Therefore, for rooms with windows and doors (with glass), you will need to consider using shades, blinds, drapes, etc. that can offer as much light control as possible. Full blackout drapes and shades are offered from many sources and offer a means to help with achieving good light control. Interior room lights also are an important consideration. Using dimmers and directional lights (e.g., small spot lights) can help control the amount light reaching the screen. Also keeping the lights along the sides walls of the HT can cause less issues than when lights are located at the back of the room (opposite the screen location) or at any location that can directly illuminate the screen. You can do a test of the effect of room lighting once the screen is setup and in it’s final position, while keeping the projector turned off, and with the HT room lighting (from exterior or interior light sources) as it would be for watching a movie. Now when you look at the screen from your normal viewing location consider that this is the blackest blacks you will be able to get in your projected video under those lighting conditions. For rooms where full light control is not possible, especially from exterior light sources, then daytime use of the HT may be limited to less serious viewing where the projector is operated in a high brightness mode to help overcome the ambient light and more serious movie viewing is reserved for the nighttime where exterior light is no long an issue and the projector can be operated in a mode to produce a more accurate image.
2. In addition to controlling room lighting, using dark colors for the room’s walls and ceiling and floor covering helps in achieving the blackest blacks within the projected image. This is the case since any light source, even including the brighter elements in the projected image itself, can be reflected around the room from light colored room surfaces and degrade (i.e., wash out) the darkest elements of the image being viewed from the screen.
3. When deciding where to locate the projection screen you also need to ensure that there will be a viable mounting location for the projector. As a starting point look at the proposed room layout and draw a line perpendicular from the center of the screen to the opposite (i.e., rear) wall. Ideally the projector will be located somewhere along this line. You need to decide what your options will be for mounting the projector. Remember, if you are going to ceiling mount the projector you will need an unobstructed light path from the projector to the entire surface of screen and you will need to have wiring installed in the ceiling. The other popular alternative is to mount the projector on a shelf or stand toward the rear of the room.
The Basics of Selecting a Projector and a Screen
Most modern home theater oriented projectors have a native aspect ratio of 16 x 9 (or 1.78:1). This is the global standard for High Definition TV and in most cases you will want to select a projection screen that has this same aspect ratio.
I must also note that some home theater enthusiasts have elected to install ‘scope’ screens with an aspect ratio of 2.35:1 or 2.40:1 to better match the proportions of cinemascope movies. Also many business class projectors have a native 16 x 10 (1.6:1) aspect ratio but can display video in a standard 1.78:1 aspect ratio.
Except as specifically noted, for the following discussion I will assume that both the projector and the screen will have a HDTV standard 1.78:1 aspect ratio.
The appropriate screen size will depend on the room size, the expected viewing distance, the flexibility for the projector mounting location and the capabilities and limitations of the specific projector to be used. If you first select the screen size and location that best fits into your room, then you will need to take this into account when selecting the projector. Likewise, if you have already selected the projector then you must understand its capabilities and limitations when selecting the appropriate screen size.
A good starting point is to draw a layout for your HT room and decide on what would the best location for the screen. If you already own the screen then you already know its size, otherwise you must decide on what size screen you would really like to have. Remember that bigger isn’t necessarily better, and if you don’t known how to select the ideal screen size, then one rule of thumb applicable for use with 1080p projectors is to use a screen with a diagonal size that is about 0.84 x the viewing distance (this is based on a recommendation from THX for what they consider the “ideal” screen size). For example if the viewing distance is 12 ft. (144 inches) then this rule-of-thumb (i.e., 0.84 x 144 inches) would suggest using a 120 inch screen (diagonal size with a 1.78 aspect ratio). Another industry rule of thumb for screen size comes from the Society of Motion Picture and Television Engineers (SMPTE) where they recommend the minimum
screen size be 0.6 x viewing distance. For the above example of a 12 ft. viewing distance the SMPTE suggestion is the screen size should be at least 86 inches. For a commercial movie theater type of experience, I have found the THX recommendation for the ‘ideal’ screen size to be appropriate. However, I like to sit 40% to 50% of the way back from the screen in most commercial cinemas and those that prefer to sit in the last row may feel more comfortable with a smaller screen size that is closer to the SMPTE suggestion for a minimum screen size.
When reviewing the specifications for a given projector you will need to determine if it will work with your desired screen size and available projector mounting locations:
a. Will it project an image of the desired size to fill the screen from the projector-to-screen throw distance you have available. This relates to the “throw ratio” for the specific projector. If a projector specifies, for example, a range of values for the throw ratio (i.e., using the projector’s zoom lens) of 1.3 to 2.0 that means the projector can be located anywhere from 1.3 to 2.0 times the screen width (not diagonal measurement) back from the screen. As an example, when a 120 inch (diagonal) screen is being used, it will have a width for the viewable area of about 104 inches. If, for this example, your room layout dictates that you locate the projector exactly 12 feet (i.e., 144 inches) from the screen, then you need to use a projector that can support a throw ratio of 144/104 = 1.38 to fill the viewable area of the 120 inch screen.
b. You will need to determine where to vertically position the screen on the wall. The general recommendation is to position the screen such that the eye level of the viewers (typically about 40 inches up from the floor for seated adult viewers) will fall about 1/3 of the way up from the bottom of the screen. For example, with a 120 inch (diagonal) screen, which is about 59 inches high (viewable area), then the recommendation is that 1/3 of the way up from the bottom of the screen (almost 20 inches) should fall at about 40 inches above the floor. Or in other words the bottom of the screen in this example would fall about (40 – 20 =) 20 inches above the floor. This is only a general suggestion and positioning the screen a little higher or lower, in order to accommodate such things as a center channel speaker below or above the screen, is frequently done in may home theaters. Once you decide on the screen size and location, then note the distance from the ceiling to the top of the screen (to the viewable area of the screen excluding any frame or housing above viewable screen surface).
c. Once the screen’s desired size and projector to screen distance are determined then you will need to determine what your options are for the projector’s vertical location, relative to the top of the screen. The options for vertical position can be more constrained for rooms with low a ceiling height. Attempting to identify those projectors which would be compatible with your proposed screen location and whatever constraints you may have on the projector’s mounting location will require knowledge of the candidate projector’s “vertical offset” and the ”vertical lens shift” capabilities. Projectors typically will project an image that is offset upward then the projector is sitting on a table in the upright position or offset the image downward when the projector is ceiling mounted in a inverted position. The figure below illustrates the effect of vertical offset where the top figure illustrates the case of a projector with zero offset and the lower figure is for the case of a projector having a non-zero offset that is mounted in the inverted position (i.e., ceiling mounted). For a projector of the type illustration in the lower figure, the projector would need to raised to a higher position to center the image on the screen due to the projector’s offset of the projected image. For example, an Optoma HD25 is an inexpensive DLP projector that has no lens shift adjustment and is specified to have an offset of 116%. This 116% value (as used by Optoma) indicates that when ceiling mounted this projector must be positioned (1.16 x screen height) above the bottom of the screen or in other words 16% of the screen height above the top of the screen. For example, when a 120 inch (diagonal) screen is being used, which is 59 inches high, the projector (measured to the center of the lens) would need to be mounted approx. (0.16 x 59”=) 9.44 inches above the top edge of the projected image (i.e., top of screen). For this projector, this is the only vertical position for this size screen that will produce an image with the desired rectangular geometry on the screen. Note that you must carefully read the manufacturer’s specification for the context of a given projector’s specified offset value since some may list it as measured from the center of the screen, some from the bottom of the screen and some from the top of the screen. Also remember the offset value listed by the manufacturer must be applied in the appropriate context of either the projector being ceiling mounted, in the inverted position, vs. mounted upright on a table or shelf.
d. Moving above entry level models, most projectors offer a vertical lens shift adjustment that allows the user to adjust the offset to provide flexibility in the vertical mounting position. Some such projectors, such as the BenQ W1070 (one of the very few entry-level models offering vertical lens shift), have only a very limited range vertical lens shift adjustment, which for this BenQ model allows the image to be shifted vertically only 15% of the screen height. Thus for a 120 inch diagonal screen the BenQ W1070’s vertical lens shift would only be able to adjust the vertical position by a total of just under than 9 inches. Also given this BenQ projector has a fairly large offset, when ceiling mounted it would need to be located between 3 inches and 11.9 inches above the top of the screen. Certain other projectors (e.g., Epson 5020UB) offer a very wide range vertical lens shift adjustment. This Epson model with the vertical lens shift adjustment at near its center position has a lens offset such that image will be at the correct vertical position when the projector is level with the top of the screen, for a ceiling mounted projector, or level with the bottom of the screen for a table or shelf mounted projector. The 5020UB’s vertical lens has a very wide range adjustment (i.e., moving the image both higher and lower) that allows a ceiling mounted 5020UB to be positioned (when using the example 120 inch screen) anywhere from near the bottom edge of the screen to about 26 inches above the top of the screen. These limits are the maximum vertical lens shift values possible and assume that no horizontal lens shift is also being used. Also using extreme settings for lens shift can in general, and not specific to just the above Epson model, result in some image compromises as discussed in THIS ARTICLE.
e. You will need to determine if your HT room will support a mounting location for the projector that is truly centered with the screen at a reasonable projector-to-screen throw distance. If it does, then a projector lacking a horizontal lens shift adjustment could be used. However, it your room’s layout will require the projector to mounted off center from the screen, then the projector must have a horizontal lens shift adjustment with enough range to accommodate the horizontal offset from the screen’s center. Many projectors in the mid-price and higher price range offer both vertical and horizontal lens shift adjustments, while some models may only offer a vertical adjustment. Also when both vertical and horizontal lens shift must be used then it can be difficult to determine, based on the manufacturer’s published specifications, exactly how much of each will actually be available. This is because there is an interaction between these two adjustment such that use of vertical lens shift reduces the range of available horizontal lens shift and vice versa.. If you only need, for example, to use 20% of the available maximum vertical lens shift then the range of the horizontal lens shift may be reduced by perhaps 10% to 20% (the actual amount varies by projector). Most Epson and JVC 1080p home theater class projectors offer a fairly wide range horizontal lens shift adjustment. For example, the Epson 5020UB allows the projector to be positioned anywhere between the screen’s horizontal center and just short of the right or left edge of the screen. For a 120 inch (diagonal) screen this means that as a maximum (assuming vertical lens shift is not also being used) the 5020UB projector can be located up to 49 inches to the right or left of the center position. Many other current and past Epson models have a similar capability. Modern JVC projectors, such as the JVC DLA-X35, offer a maximum horizontal lens shift of 34% of the screen width. For the example of a 120 inch screen, this would permit the projector to be positioned as much as approx. (.34 x 104 =) 35 inches to the right or left of the screen’s horizontal center (as long as no vertical lens shift is used). As a third example, the Sony VPL-HW50ES offers a maximum horizontal lens shift of 25% of the screen width which for a 120 inch (diagonal) screen would permit the projector to be positioned as much as (.25 x 104 =) 26 inches to the right or left of the screen’s horizontal center (as long as no vertical lens shift is used).
Once you understand what capabilities you will need in order for the projector to be able to project an image that will be the correct size and position for your screen and with proper rectangular geometry, it is time to investigate which projectors will work for your layout.
Most projector manufacturers offer some sort of distance calculator on their web site to assist in determining the correct projector mounting locations (or range of locations). See the web links below for the calculators available from several of the popular projector manufacturers. Also once you narrow your choice of projectors you may want to download the user manual for those models you are considering. Generally the user manual will include tables with the projector’s setup information for various standard screen sizes.
Projector Distance Calculators – Manufacturer’s Web Sites
BenQ (Throw Ratio Calculator)
Epson (Image Size Calculator)
JVC (Lens Calculator)
Optoma (first go the page for the specific projector model and then select “distance calculator”)
Panasonic (Throw Distance Calculator – download app)
Sony (Projector Installation Simulator)
The above discussion has only addressed selecting a projector that will project an image that matches the size of the screen you have selected and will be able to do that with the correct image geometry. The other major consideration is selecting a screen and projector combination that will provide a bright enough image. I covered that topic in some detail in my earlier blog (HERE
) from September 2011. Finally, I suggest you read the Project Reviews "Best Home Theater Projectors Report - 2013
" to learn about the performance capabilities of the projectors within the price range you are considering.
This discussion will be continued in my August blog where I will discuss mounting the projector and adjusting the mount and optics to achieve the correct image position and geometry.