A shortpass filter is an optical filter that allows shorter wavelengths to pass through while blocking longer wavelengths.
These optical filters are commonly used in imaging systems, fluorescence systems, machine vision, optical sensors, color measurement, environmental monitoring, scientific instruments, and custom optical assemblies.
What Is a Shortpass Filter?
A shortpass filter is an optical filter designed to transmit shorter wavelengths and block longer wavelengths.
In simple words, a shortpass optical filters works like a wavelength separator.
It allows light below a selected cut-off wavelength to pass through, while reducing or blocking light above that wavelength.
For example, a 700 nm shortpass filter is designed to transmit shorter wavelengths below the cut-off region and block longer wavelengths above it.
Why It Used?
Shortpass filters are used when an optical system needs to remove longer wavelength light and keep shorter wavelength light.
They can help improve image contrast, reduce unwanted background light, separate wavelength ranges, and support more accurate optical detection.
Common applications include:
- Machine vision
- Fluorescence imaging
- Biomedical instruments
- Optical sensors
- Color measurement
- Environmental monitoring
- Digital imaging
- Scientific instruments
- Laser and LED systems
- Custom optical assemblies
How Does an Optical Filter Work?
An optical filters has two main regions:
| Region | Function |
|---|---|
| Transmission Region | Allows shorter wavelengths before the cut-off point to pass through |
| Blocking Region | Blocks longer wavelengths after the cut-off point |
The transition between these two regions is called the spectral edge.
A good shortpass optical filters usually has:
- High transmission in the passband
- Strong blocking in the rejection band
- Suitable optical density, or OD
- Stable coating performance
- Cut-off wavelength matched to the application
Key Specifications of a Shortpass Filter
When selecting a shortpass filter, customers usually need to consider several key specifications.
| Specification | Simple Explanation |
|---|---|
| Cut-Off Wavelength | The wavelength where the filter starts to block longer wavelengths |
| Transmission Range | The shorter wavelength range that passes through the filter |
| Blocking Range | The longer wavelength range that should be blocked |
| Transmittance | How much light passes through in the transmission range |
| Optical Density / OD | How strongly unwanted wavelengths are blocked |
| Substrate Material | The base optical material of the filter |
| Size and Thickness | Physical dimensions of the filter |
| Angle of Incidence | The angle at which light enters the filter |
| Coating Requirement | Filter coating design based on wavelength and application |
Common Types of Filters
These optical filters can be supplied in standard or customized designs depending on the required wavelength range and system use.
Common shortpass filters types include:
- UV optical filters
- Visible optical filters
- NIR optical filters
- High-transmission optical filters
- High-OD optical filters
- Custom optical filters
UV Shortpass Filter
A UV optical filters is designed to transmit ultraviolet wavelengths while blocking longer visible or infrared wavelengths.
Common applications:
- UV imaging systems
- Fluorescence systems
- Biomedical instruments
- Scientific measurement systems
- Optical detection systems
Visible Shortpass Filter
A visible optical filters is used to transmit selected visible wavelength ranges and block longer wavelengths.
For example, it may be used to transmit blue or green light while blocking red or near-infrared light, depending on the cut-off wavelength.
Common applications:
- Machine vision
- Digital imaging
- Color measurement
- Optical inspection
- Camera systems
- Display and lighting measurement
NIR Shortpass Filter
A near-infrared, or NIR, shortpass optical filters is designed to transmit shorter wavelengths and block selected longer near-infrared wavelengths.
Common applications:
- NIR imaging systems
- Optical sensors
- Biometric systems
- Environmental monitoring
- Scientific instruments
- Custom detection systems
High-OD Shortpass Filter
A high-OD optical filters is used when the system needs stronger blocking of unwanted longer wavelengths.
OD, or optical density, describes how strongly the filter blocks light in the rejection range.
A higher OD value means stronger blocking.
Common applications:
- Fluorescence imaging
- Sensitive optical detection
- Laser-related optical systems
- Biomedical measurement
- Scientific instruments
Custom Shortpass Filter
A custom optical filters is designed based on the customer’s specific wavelength and mechanical requirements.
Custom options may include:
- Custom cut-off wavelength
- Custom transmission range
- Custom blocking range
- Custom OD level
- Custom size and thickness
- Custom substrate material
- Custom shape
- Custom mounting or ring design
Custom optical filters are useful when standard filters cannot fully match the optical system requirement.
Shortpass Filter vs Longpass Filter vs Bandpass Filter
Shortpass filters are different from longpass and bandpass filters.
| Filter Type | What It Transmits | What It Blocks | Simple Explanation |
|---|---|---|---|
| Shortpass Filter | Shorter wavelengths | Longer wavelengths | Allows light before the cut-off wavelength to pass |
| Longpass Filter | Longer wavelengths | Shorter wavelengths | Allows light after the cut-on wavelength to pass |
| Bandpass Filter | A selected wavelength band | Wavelengths outside the band | Allows only a specific wavelength range to pass |
In simple terms:
A shortpass filter keeps the shorter wavelengths.
A longpass filter keeps the longer wavelengths.
A bandpass filter keeps only a selected middle wavelength range.
Typical Shortpass Filter Specifications
| Item | Example Specification |
|---|---|
| Filter Type | Shortpass filter |
| Cut-Off Wavelength | 400 nm / 650 nm / 850 nm / custom |
| Transmittance | T ≥ 90%, or based on requirement |
| Blocking Range | Based on cut-off wavelength and application |
| Optical Density | OD2 / OD4 / OD6, or custom |
| Substrate | Optical glass / fused silica / custom material |
| Shape | Round / square / rectangular |
| Size | Ø25 mm / 50 × 50 mm / custom |
| Thickness | 1.0 mm / 2.0 mm / custom |
| Coating | Shortpass filter coating |
| Mounting | Unmounted / mounted / custom ring |
| Application | Imaging / sensing / fluorescence / machine vision / color measurement |
Application Examples
| Application | How Shortpass Filter Helps |
|---|---|
| Machine Vision | Helps separate useful light from unwanted longer wavelength signals |
| Fluorescence Imaging | Helps block longer wavelength background light when required |
| Biomedical Instruments | Supports selective wavelength filtering for detection or imaging |
| Digital Imaging | Helps control color or spectral response |
| Color Measurement | Helps select the required shorter wavelength range |
| Environmental Monitoring | Supports optical sensing and wavelength separation |
| Optical Sensors | Helps reduce unwanted long-wavelength interference |
| Scientific Instruments | Supports controlled optical measurement and testing |
What Information Should You Provide Before Requesting a Quote?
To request a optical filters, it is helpful to provide:
- Required cut-off wavelength
- Transmission wavelength range
- Blocking wavelength range
- Transmittance requirement
- Optical density, or OD requirement
- Filter size and thickness
- Shape: round, square, rectangular, or custom
- Substrate material, if required
- Angle of incidence
- Surface quality requirement
- Quantity
- Mounted or unmounted requirement
- Application, such as imaging, fluorescence, sensing, or machine vision
- Drawing or specification, if available
If you are not sure which optical filters is suitable, you can provide your application and target wavelength range. Our team can help review the requirement and suggest a suitable filter option.
Conclusion
A shortpass filter is used to transmit shorter wavelengths and block longer wavelengths.
It is commonly used in machine vision, fluorescence imaging, biomedical instruments, optical sensors, color measurement, environmental monitoring, scientific instruments, and custom optical systems.
The right optical filters depends on the cut-off wavelength, transmission range, blocking range, OD level, size, substrate, angle of incidence, and final application.
Shape Optics Technologies supplies shortpass optical filters, longpass filters, bandpass filters, optical coatings, coated filters, and custom optical filter components based on customer requirements.
Contact us to discuss your custom optical filters requirements.