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|PI875 Service Manual|
Note 7 : Blemishes
Non-uniformities in the mirror array or optical window may result in localized variations in the
luminous output (i.e., blemishes) across the surface of the device when viewed in an optical imaging
environment. Such localized non-uniformities may result from a varity of sources, including variations
in tilt angles, mirror cupping, foreign particles on the array or inside window surface, window
scratches, etc. The magnitude of the projected non-uniformities is highly system dependent. Practicaly
speaking, blemishes arising from window defects will be of a common size which depends critically
on the system optics. The effect of defect size is generally limited to the differential brightness
associated with the defect for scratch, dig and particle defects of practical size. Restrictions on
location within the array, maximum count, and differential brightness are defined only for particular
systems, and may be found in the applicable product image quality specification.
Note 8 : Placement of Active Area within Package
The positioning of the die active area within the hermetic package is delineated in Figure 6,
Figure 7, and Figure 9. Practical optical systems will need to comprehend a maximum of 0.003"
variability in the focal plane of the modulating element referenced to the datum [A], Figure 7 in the
absence of any alignment mechanism in the system. if some means of rotational alignment with respect
to the system optical axis is comprehended by the design, this variability falls to 0.0014" per Figure
7, datum [K]. The in-plane rotational angle between active area and package datum, Figure 9, note 3 is
0.0 +/- 0.8 degrees. The true position tolerance relative to the package datum is 0.5mm.
Note 9 : Window Optical Properties
The optical quality of the window is an important contributor to the quality of the projected
image. To meet the uniformity requirements discussed previously, the minimum window opening
defined in Figure 9 must be free of striae, bubbles, inclusions, birefringence, and particles which
might degrade the optical performance of the packaged DMD. Visibility of scratch, dig, and particle
defects are highly system dependent. The window opening must not block any dump light from the
active area. To maximize contrast, the window is coated on both sides by an anti-reflective coating.
The average reflectance shall be less than 0.5% for wavelengths of 420-700 nanometers and any angle
between normal and 30 degrees. The index of refrection is specified for a light wavelength of 545
nanometers.
_ViewSonic Corporation _
: Confidential - Do Not Copy *
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