Samsung SP-F10M - Manual (Page 14)

2-4 Installation and Connection
2-4 Zoom and Focus Adjustment
The size of your screen determines the distance you set your projector from the screen.
If you do not install your projector at the projection distance specified in the Screen Size and Projection Distance table in
Section 2-5, you will not be able to adjust the focus correctly.
Zoom Knob : You can adjust the size of the image within the
zoom range by manipulating the Zoom Knob.
Focus Ring : Focus the picture on the screen using the Focus
Ring.