BenQ TH670s - Manual (Page 17)

Positioning your projector 17
Obtaining a preferred projected image size
The distance from the projector lens to the screen, the zoom setting (if available), and
the video format each factors in the projected image size.
The projector should always be placed horizontally level (like flat on a table), and
positioned directly perpendicular (90° right-angle square) to the horizontal center of
the screen. This prevents image distortion caused by angled projections (or projecting
onto angled surfaces).
If the projector is mounted on a ceiling, it must be mounted upside-down so that it
projects at a slightly downward angle.
You can see from the diagram on page
18 , that this type of projection causes the
bottom edge of the projected image to be vertically offset from the horizontal plane
of the projector. When ceiling mounted, this refers to the top edge of the projected
image.
If the projector is positioned further away from the screen, the projected image size
increases, and the vertical offset also increases proportionately.
When determining the position of the screen and projector, you will need to account
for both the projected image size and the vertical offset dimension, which are
proportional to the projection distance.
BenQ has provided a table of screen sizes to assist you in determining the ideal
location for your projector. There are two dimensions to consider, the perpendicular
horizontal distance from the center of the screen (projection distance), and the
vertical offset height of the projector from the horizontal edge of the screen (offset).