Product description:

The optical low-pass filter (OLPF) is laminated with several pieces of quartz, which uses the birefringence of quartz to suppress the moire caused by the spatial frequency that is too close to the imaging and image sensor. Generally, it is plated on the quartz surface, and the infrared cut film (IRcut) is coated with an anti-reflection film on the other side. If absorbing blue glass is used, it can be placed between the quartz plates to get a better image reflection.
 

Competitive advantages:

‧ Customized OLPF design capabilities
‧ Provide the highest quality coating and optical capabilities
‧ Good weather resistance
 

Applications:

‧ Surveillance camera module
‧ Monocular camera module
‧ High-end camera module

OLPF (Optical Low Pass Filter) Usage:

When converting from analog film to digital cameras or camcorders, it is necessary to place an OLPF in front of the photodetector (CCD or CMOS) to reduce moiré patterns.

General structure of OLPF:

The cause of moiré patterns:

The image below is a good example, where lines of different frequencies overlap, resulting in high-frequency interference. When the upper layer lines are shifted to specific positions, a new wave-like interference pattern is generated. In photography, moiré patterns can be observed when capturing objects with highly regular patterns (e.g., fishnet) or scenes with repetitive details (e.g., vertical lines in architecture).

Why OLPF can improve this issue involves the principles of sampling. When converting continuous data to discrete digital data, it must comply with the Nyquist sampling theorem. Insufficient sampling can result in moiré patterns. The purpose of OLPF is to reduce the sampling frequency of the lens, ensuring that the sampling of the photodetector (CCD or CMOS) meets the Nyquist sampling theorem. The specific approach is as follows:

After passing through the OLPF, a light beam will be divided into four beams, and the sampling frequency of the lens will be reduced to an appropriate value.