5 Key Takeaways
- Schott optical filters provide precise spectral control for imaging, sensing and spectroscopy.
- Each filter glass type has a defined transmission curve, making selection highly application‑specific.
- Longpass, shortpass, bandpass, neutral density and heat‑absorbing glasses each serve different optical roles.
- Understanding wavelength ranges, system illumination and detector sensitivity is essential when choosing a filter.
- Schott’s colour glass portfolio offers long‑term stability, excellent homogeneity and predictable performance.
Introduction
Following on from last month’s blog Schott N‑BK7 Glass Explained, this blog explores another cornerstone of optical design: Schott filter glass.
While N‑BK7 provides a stable, high‑quality substrate for lenses, windows and prisms, Schott’s extensive filter glass range enables engineers and scientists to shape light with precision. From isolating fluorescence bands to blocking infrared radiation, these filters are essential in imaging, spectroscopy, machine vision and analytical instrumentation.
This article explains how Schott filters work, the differences between filter types, and how to select the right material for your application.
What Makes Schott Filters Unique?
Schott’s colour glass filters are engineered to deliver stable, repeatable spectral performance across the ultraviolet, visible and near‑infrared regions. Unlike thin‑film interference filters, which rely on deposited coatings, Schott filters achieve their spectral behaviour through intrinsic material absorption. This gives them several advantages:
- Long‑term stability: absorption characteristics do not drift over time.
- Excellent homogeneity: consistent transmission across the aperture.
- High environmental durability: resistance to humidity, temperature cycling and UV exposure.
These properties make Schott filters ideal for demanding industrial and scientific environments where reliability is critical.
Understanding Filter Types
Schott’s portfolio covers a wide range of spectral functions. Choosing the right one begins with understanding the main filter categories. We’ve listed these below:
Longpass Filters (LP)
Longpass filters transmit wavelengths above a defined cut‑on point while absorbing shorter wavelengths.
Applications include fluorescence emission, NIR imaging and environmental sensing.
Examples: RG, OG and GG series.
Shortpass Filters (SP)
Shortpass filters transmit wavelengths below a defined cut‑off point and block longer wavelengths.
They are used for UV imaging, blocking unwanted IR and in multispectral cameras.
Examples: BG and UG series.
Bandpass Filters (BP)
Bandpass filters transmit a specific wavelength band while absorbing both shorter and longer wavelengths and are used in applications such as fluorescence excitation, gas analysis and spectroscopy.
Examples: BG and VG series.
Neutral Density (ND) Filters
ND filters attenuate light evenly across a broad spectral range without altering colour balance and are ideal for exposure control, laser attenuation and imaging calibration.
Examples: NG series.
Heat‑Absorbing Filters
These filters absorb infrared radiation to protect sensors and optical assemblies from thermal load in systems such as illumination, projection and high‑intensity lighting.
Examples: KG series.
Key Considerations When Selecting a Schott Filter
Choosing the right filter is not simply a matter of selecting a wavelength. Several practical factors influence performance.
1. Wavelength Requirements
Start with the spectral range your system needs to transmit or block. Schott provides detailed transmission curves for each glass type, enabling precise matching to:
- excitation/emission bands
- detector sensitivity
- illumination source spectrum.
For spectroscopy, narrow and well‑defined transmission bands are essential. For imaging, broader and smoother curves may be preferable.
2. Optical Path and System Geometry
Filter thickness affects transmission and cut‑on/cut‑off behaviour. In high‑precision systems, even small variations can shift spectral performance. Consider:
- angle of incidence
- beam divergence
- required clear aperture.
Absorptive filters are generally more angle‑tolerant than interference coatings, making them suitable for wide‑field imaging.
3. Environmental Conditions
Industrial and outdoor systems may face:
- humidity
- temperature cycling
- UV exposure.
Schott’s colour glass filters are inherently stable under these conditions, maintaining predictable performance over long service lifetimes.
4. Mechanical and Thermal Requirements
Some filters, such as KG heat‑absorbing glass, are designed to withstand high thermal loads. Others prioritise optical purity or low autofluorescence. Matching material properties to system demands ensures long‑term reliability.
5. Integration with Other Optics
Filters are often paired with:
- N‑BK7 lenses and windows
- AR‑coated substrates
- dichroic beam splitters.
Ensuring compatibility across refractive indices, thicknesses and mounting constraints avoids unwanted reflections or spectral shifts.
Schott Filters in Imaging
In imaging systems—machine vision, microscopy, remote sensing—filters play a crucial role in controlling contrast and isolating features.
Machine Vision
Filters help suppress ambient light, isolate LED illumination bands and improve signal‑to‑noise ratios. Longpass and bandpass filters are particularly common.
Microscopy and Fluorescence Imaging
Schott’s UG, BG and VG glasses are widely used for excitation and emission control. Their stable absorption profiles ensure consistent imaging results across long experimental runs.
Hyperspectral and Multispectral Imaging
Precise spectral separation is essential. Schott’s broad portfolio allows designers to build custom filter stacks tailored to specific wavelength bands.
Schott Filters in Spectroscopy
Spectroscopy demands high spectral purity and predictable transmission. Schott’s absorptive filters excel in:
- fluorescence spectroscopy – isolating emission bands
- Raman spectroscopy – blocking excitation wavelengths
- gas and chemical analysis – selecting narrow spectral windows
- environmental monitoring – UV and NIR discrimination.
Because the absorption characteristics are intrinsic to the glass, performance remains stable even under intense illumination.
Practical Steps for Choosing Your Filter
- Define your wavelength goals – what must pass, and what must be blocked?
- Review Schott’s transmission curves – match glass types to your spectral needs.
- Consider system geometry – angle, beam shape and optical path length.
- Assess environmental conditions – temperature, humidity, UV exposure.
- Check mechanical constraints – thickness, size, mounting, thermal load.
- Consult a supplier such as UQG Optics – for custom sizes, polishing, or AR‑coating options.
Conclusion
Schott filter glass is a powerful tool for controlling light in imaging and spectroscopy. Its stability, homogeneity and predictable spectral behaviour make it a trusted choice across scientific, industrial and analytical applications. Whether you’re isolating fluorescence bands, protecting sensors from heat, or shaping illumination for machine vision, selecting the right Schott filter ensures your optical system will perform with accuracy and reliability.
Next steps
Ask UQG Optics about identifying the best Schott glass filter for your application. Alternatively, explore our range of Schott filters.