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 In
high-quality digital maging systems, optical low-pass filters (OLPF) are
used to eliminate color Moire fringes. An OLPF cuts off the
lens MTF above
the sampling frequency of the imager resulting an overall MTF curve that
approximates a step function in spatial domain. IR cut-off function is
often incorporated into OLPF as well. See CCD/CMOS lens selection guide for discussion of OLPF and its impact on image quality.
Download an application note on optical low-pass filters.
OLPFs are made of several cemented layers of optical quartz material. An IR
cut-off coating and anti-reflection coating are applied to the external
surfaces. If the IR cut-off filter type is absorptive, the IR glass is
inserted between the quartz layers. Custom OLPF sizes and designs are also
available.
General Specifications:
| Parameter |
Value |
| Default unit |
mm |
| Default dimensional tolerance |
+/-0.2mm |
| Coating |
External surfaces single
layer MgF2, unless otherwise indicated |
| Effective area |
90% |
| Surface flatness |
3 fringes |
| Inclusion and dig |
<40 µm within the
effective area |
| Scratch width |
<10 µm within the
effective area |
| Chip and bevel |
Allowed only if outside the effective area |
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