Bena Optics is a long pass filter supplier and manufacturer providing longpass optical filters for fluorescence, imaging, laser systems, and machine vision. Our long pass filters are designed to transmit wavelengths above the specified cut‑on wavelength while blocking shorter wavelengths with high attenuation. Typical blocking levels are available up to OD4–OD6 (option), with coating designs optimized for stable performance at your working angle.
Since spectral response shifts with angle of incidence, we can tailor the design to control angle shift and meet your system’s bandwidth and transmission targets. We support custom long‑pass optical filter requirements including wavelength, size, substrate, thickness, surface quality, and AR/coating options. Send your target cut‑on, operating angle, and environment to get a fast recommendation and quote.
Features of Long Pass Filter
Long pass filters have excellent characteristics such as high transmittance, extremely low loss, high stability, and low thermal expansion coefficient. These features make them widely applicable in various fields, including optics, electronics, and biomedical fields. For example, in fluorescence microscopy imaging, long pass filters can be used to block excitation light, allowing only the fluorescence signal to pass through, thereby improving the contrast and clarity of the image.
The application areas of long pass filters are very broad, including spectral analysis, laser technology, biomedical imaging, optical communication, environmental monitoring, and remote sensing. In optical systems, components such as optical prisms and filters may be used depending on system design requirements. In spectral analysis, long pass filters are used to separate and detect light of specific wavelengths; in laser technology, they are used to optimize the quality and stability of laser beams; in biomedical imaging, they help researchers more accurately identify and analyze fluorescent markers in cells or tissues.
OD (Optical Density) describes blocking strength in the stopband: OD = −log10(T). For example, OD4 ≈ .01% transmission, OD6 ≈ .0001%. Select OD based on stray light level and detector sensitivity. Many imaging/fluorescence systems use OD4–OD6 depending on how well excitation light must be suppressed.
Read more about Optical Density (OD) for Optical Filters: What OD Level Should You Select?
Long pass filter (LPF/longpass filter): transmits wavelengths longer than the cut-on wavelength.
Short pass filter (SPF): transmits wavelengths shorter than a cut-off wavelength.
Bandpass filter (BPF): transmits only a specific band between two edges and blocks outside that band.
Selection depends on whether you need edge separation (LPF/SPF) or a narrow spectral window (BPF).
Read more about Long Pass Filter vs Short Pass Filter vs Bandpass Filter
For interference-coated longpass optical filters, increasing the angle of incidence typically shifts the spectral edge toward shorter wavelengths (blue shift). This angle shift can move the cut-on point and reduce separation performance, especially in wide-angle or converging beams.
Read more about How Angle of Incidence (AOI) Affects Long Pass Filter Performance
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