What types of lens filters are there?

Why use a Lens filter?

Lens filters are used to control/attenuate parts of the spectrum (colours of light) before they enter the lens/camera.  This can be in the UV (low end), visible (mid range) or NIR (high end) of CCD/CMOS camera sensitivity.

There are an almost infinite number of different filters.  They are usually described as low-pass (Longpass), high-pass (Shortpass) or band-pass. The full description of a filter specifies a particular wavelength of light (the cut-off point or band centre) followed by low-pass, high-pass or band-pass.

The cut-off or centre wavelength is never absolute.  All filters have what is called a ‘roll-off’ characteristic that is usually available graphically.  This describes how accurately the filter is eliminating or passing unwanted light.  Generally, the steeper the roll-off, the higher the quality of the filter

Midwest Optical Lens Filters Range:

Midwest Optical Systems (MidOpt) is the worlds leading resource for off-the-shelf and custom machine vision filters, lenses and accessories used in industrial imaging applications. Security, surveillance, scientific, medical and other markets are also served.  The filters are produced with MidOpts unique StablEDGE Technology – Learn more


BANDPASS FILTERS:  MidOpt Bandpass Filters are the simplest, quickest and most cost-effective way to improve the image contrast, repeatability, and long term stability of any industrial vision system.

MULTI BANDPASS FILTERS: MidOpt Dual Bandpass and Triple Bandpass Filters are most commonly used for security and surveillance, intelligent traffic solutions and Normalised Difference Vegetation Index (NDVI) imaging.

LONGPASS FILTERS: Longpass filters let longer visible and/or infrared wavelengths pass while blocking shorter wavelengths of light. Mainly for use in monochrome (black and white) imaging applications, they can help to improve contrast, resolution and separate colours while maximising brightness of surroundings in the vicinity of the subject under inspection or surveillance.

SHORTPASS FILTERS:  Shortpass filters are useful for improving contrast, resolution and separating colours in black and white or colour applications.

NEUTRAL DENSITY FILTERS: Light used to image any nonmetallic surface will produce polarised light in reflection, therefore the use of linear polarisers can often result in appreciable benefit in industrial imaging applications.

Sunglasses for your system, ND filters reduce light intensity without affecting apparent colour. They also allow for longer exposure times and reduced depth of field by using a wider iris opening, thus improving the separation of subject matter from background information.

POLARISING FILTERS: Polarisers are designed to reduce specular glare by passing only the light polarised in the direction perpendicular to the reflected light (glare). In addition, they help improve contrast, increase colour saturation and detect imperfections in transparent materials.

PROTECTIVE FILTERS: Available in glass or acrylic substrates, protective filters shield lenses and lighting from impact, dust and harsh environments – while blocking shorter UV wavelengths.


MidOpt Filters for Machine Vision are now enchanced with robotic precision

Enhanced image quality

Traditional filters: Drastic deformations can result from the stress caused by over tightening the mount retainer during assembly, which can lead to optical distortion, significantly impacting image quality.

The MidOpt difference: MidOpt robotic technology allows for precise torque control so that each filter can be securely placed into a mount, resulting in consistent image quality that is free of distortion.

Improved inspection process

Traditional filters: During standard inspection processes, filters are typically examined by the human eye. Individual perception can vary, the opportunity for error is high, and filters often aren’t tested with various lighting configurations or increased magnification.

The MidOpt difference: MidOpt robotic technology guarantees consistency and uniformity when inspecting scratches, digs and cosmetic defects. The inspection process incorporates greater lighting variety, increased magnification and sophisticated algorithms to maximise surface quality.