in addition, both throw distance (the distance between the projector and screen) and vertical position (the height of the projector in relation to the screen) must be determined for every new installation. both depend on the screen size and lens type you are using. make sure that the room can accommodate the required position of the projector for the chosen screen size.
1 throw distance
for any installation, an accurate throw distance (td) must be determined in order for the image to be of the right size for your screen–the farther the projector is from the screen, the larger the image. throw distance is the distance between the projector's front feet axes and the screen (figure 2.19), and is roughly equal to the horizontal width of the screen multiplied by the throw ratio of the installed lens. once you know your screen size and lens, you can estimate throw distance needed. for example:
screen width=10 feet
lens type is 0.7:1
throw distance (td)=10 feet x 0.7=7 feet
1) if your projector is slightly tilted in relation to the screen, typical for large venues or flown installations, throw distance still represents the smallest measurement between the screen and front feet. 2) for proper placement in an installation, always refer to the throw distance formula and/or chart for your lens as listed in appendix e. keep in mind that due to lens manufacturing tolerances for lens focal length, actual throw distance can vary ±5% between lenses described as having the same throw ratio
2 vertical & horizontal position
the vertical position of the projector in relation to the screen also depends on the size of the screen and the lens type. correct vertical position helps ensure that the image will be rectangular in shape rather than keystoned (having non-parallel sides) and that image focus and brightness both remain optimized.
if necessary, vertical position of the image can be offset—that is, moved up or down in relation to lens center—by using the motorized offset function. starting with no offset, the 1400 x 1050 image from this projector can be moved up or down by a maximum distance of 525 pixels, resulting in all of the image displayed above or below lens center. see table 2.1 and figure 2.20. note: not applicable to the fixed 0.73:1 lens.
the horizontal position of the image can be offset—that is, shifted left or right of lens center—by using the motorized offset function. starting with no offset, the 1400 x 1050 image from this projector can be moved left or right by a maximum distance of 350 pixels, resulting in 75% of the image displayed to one side of lens center. see table 2.1 and figure 2.21.
table 2.1. maximum amount of image offset from lens center
1) offsets are not available with 0.73:1 fixed lens. 2) when offset movement is stated as a percentage (see left columns), this represents the percentage of ?image height or?image width.
all offset centering is ±7%.
1) if the image becomes keystoned or exhibits uneven brightness, the projector may simply be too high or low in relation to the screen. 2) recommended offset ranges can be exceeded, however this may affect image quality. 3) simultaneous horizontal and vertical offset limits the adjustment range of each. 4) offset can vary by ±7% and may be affected by the degree of zoom currently in use.
3 tilting the projector
figure 2. 22. the projector can be rotated and mounted at any vertical angle—i.e., you can tilt the face of the projector up or down as much as desired for your installation. side-to-side tilt, however, must not exceed 15°. this limit ensures that the lamp in the projector operates properly and safely. to prevent heat waves in your projected image, always make sure that exhaust air from the projector vents away from the lens.
for permanent ceiling mount installations, use the christie ceiling mount fixture designed for your projector. for more information, contact your dealer.
4 folded optics
in rear screen applications (figure 2.23)where space behind the projector is limited, a mirror may be used to fold the optical path. the position of the projector and mirror must be accurately set. consult your dealer or christie for details.
