The lens holder has to be adjusted so that the “sharp focus plane” of the projected image falls together with the plane of the screen (Fp1→Fp2). This is achieved by changing the distance between the DMD plane and the lens plane (Lp1→Lp2). The closer the lens plane comes to the DMD plane the further the sharp focus plane will be. It can occur that you won't be able to get a complete focused image on the screen due to a tilt (or swing) of the lens plane with respect to the DMD plane. This is also known as Scheimpflug's law. To solve this the lens plane must be placed parallel with the DMD plane. This can be achieved by turning the lens holder to remove the tilt (or swing) between lens plane and DMD plane (Lp3→Lp4).
Image 6–1Image 6–2
Scheimpflug principle
The "plane of sharp focus" can be changed so that any plane can be brought into sharp focus. When the DMD plane and lens plane are parallel, the plane of sharp focus will also be parallel to these two planes. If, however, the lens plane is tilted with respect to the DMD plane, the plane of sharp focus will also be tilted according to geometrical and optical properties. The DMD plane, the principal lens plane and the sharp focus plane will intersect in a line below the projector for downward lens tilt.
Scheimpflug adjustment points
Image 6–3Scheimpflug adjustments points on Lens holder - Projector front view. (Shape of the lens may vary with the model)
1
Scheimpflug adjustment screw
2
Scheimpflug adjustment screw
3
Scheimpflug adjustment screw
A
Scheimpflug lock nut
B
Scheimpflug lock nut
C
Scheimpflug lock nut
When to apply Scheimpflug?
Only apply a Scheimpflug correction in case the overall focus of the projected image is not equally sharp (can be caused if the projector is NOT in parallel with the screen or a previous misaligned Scheimpflug). Take into account that the consequence of applying Scheimpflug correction upon a screen not in parallel with the projector is that the projected image differs from the rectangle shaped image. In other words “distortion” of the projected image occurs. Masking will be required to solve the distortion.
The disadvantage of Masking is loss of content. Therefore it is strongly recommended to place the projector in parallel with the projection screen and use the SHIFT functionality of the lens holder older to match the projected image with the projection screen. In case the SHIFT range is not sufficient then the projector can be tilted and Scheimpflug can be applied.
