4 Optical

In systems with one-to-one or greater magnification, designing illumination and output optics with ¹ ƒ-numbers ⁽¹⁾ƒ-numbers as small as ƒ/2.4 are practical and desirable. Matching the illumination and projection ƒ-numbers too closely can result in a significant loss of power at the focal plane (fabrication surface). Slightly under-filling the output pupil provides DMD tilt variation tolerance in an optical system. For example, illuminating with ƒ/3 into an ƒ/2.4 output allows the image of the illumination pupil to remain within the output aperture. This is discussed in more detail in Section 5.1.

TI recommends that an illumination adjustment mechanism allowing adjustment of ±2° from the nominal incident angle be employed in a system design. Typically the illumination cone is centered on an angle that is 24° from the window normal so that the output cone is centered on the DMD normal for 12° tilt angle devices. The ±2° adjustment allows the brightest orders to be moved into the output aperture.

These and other DLP optical system considerations are discussed in greater detail in the (TI DLP® System Design: Optical Module Specifications). The following sections examine considerations for high demagnification systems.