Another way to reduce is to raise the copy above the normal copy area. Build a cardboard box the same size as original copy area and mount over copy opening. By mounting your copy at this new higher level, you will create a reduced image. Size of image will vary with height of box. Focus as usual.
Image size is achieved by moving projector closer or farther away from image plane.
To ease sizing when projecting onto a wall, mount projector onto rolling cart or use Artograph Projector Floor Stand . If using certain size images frequently, mark floor with yellow tape. Position tape at desired distances and mark image size i.e. 10x simply move cart to tape mark to attain size. Always ensure that projector is perpendicular to image plane to prevent key stoning. Project grid onto wall or vertical surface and measure each corner square for like size and shape.