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Bandpass Filters

Optical bandpass filters are used to transmit a selected wavelength while attenuating (blocking) the unwanted shorter and longer wavelengths.

Knight Optical offer a range of custom optical band pass filters comprising of interference, coloured glass, gelatin, polyester, variable bandpass and edge, fluorescence, dichroic band-pass and blocking, mounted singles, and sets of mounted and unmounted.  The interference filters are made from thin films of material that have differing refractive indices and thickness, whilst the glass and gelatin have a dye within the substrate.

Custom colour glass bandpass filters:

Colour glass filters also known as “ glass colour filters” are available in a range of custom options.  Although they are relatively cheap and very stable, they have a disadvantage in that they are only available in a relatively small number of variants, and so can be restrictive in bandpass selection. Custom colour glass band-pass filters are available in the schott or equivalent  and hoya colour or equivalent filter ranges and available up to 165mm squares. These can be made into custom square and rectangular apertures or to any shape and sizes with a maximum diameter of 164mm dia. Some russian and asian equivalent colour bandpass filters are available in larger sheets up to 300x300mm squares. Custom colour glass bandpass filters can be polished thinner achieving higher transmission. Filters can also be drilled or CNC machined or coated with antireflective coating
to decrease reflections and increase transmission further.  Custom colour glass bandpass filters are primarily used in applications such as agriculture analysis, medical analysers and fluorescence applications. Custom colour glass filters also have high transmissions at selected wavelengths therefore ideal where the angle of incidence of the incident light cannot be tightly controlled.

Custom interference bandpass filters:   Knight Optical supply high quality custom interference bandpass filters that pass light of a narrow bandwidth, wavelength and reflect, or block all other light from 200nm-2000nm.  In principle interference filters can be designed and manufactured to almost any specification of centre wavelength and band pass.  Our interference bandpass filters are high quality being individual CNC scribed and hermetically sealed to form a secure stack in their rings to ensure maximum long-term stability.

View our informations sheet: Scribed interference filters

There are a host of custom options for interference filters ranging from size, mounting and performance.  Standard mounting options are generally available as 12.5mm, 12.7mm, 25mm, 25.4mm, 50mm and 50.8mm diameter although any diameter of mounted ring type can be supplied.  We also supply unmounted interference filters with edges painted with aerospace paint for stability and performance as circular, square and rectangular aperture options. Custom interference filters
can also be assembled into special shaped mounts with fixing holes for mounting directly into a camera system.  Custom performance options are available.  Peak transmission can be regulated to perform within a curtain range for consistency in setting up your instrument for example 50%+/-5%, full width half max can be controlled to within a few nanometres, and centre wavelength can be controlled to within 10% of FWHM.  Generally interference filters have 3-4 cavity designs however we can produce custom interference filters
to 7 cavity designs with stringent custom out of band blocking requirements.  Our custom narrow band interference laser-line filters are typically used in imaging applications, whilst our fluorescence and dichroic excitation and emission filters are typically used in spectroscopy, microscopy, and medical fluorescence applications.

Custom polyester and Wratten bandpass filters:  Polyester and wratten ranges of colour filters are available in a range of size options. Polyester types have the dye held in a thin sheet. Custom polyester colour filters area available in large sheet to supply bespoke custom shapes and sizes to your specific. Large 1000mm square sheets can be supplied for your own cutting requirements as they are 0.1mm thk and can easily be cut with a sharp razor blade. Custom polyester bandpass filters are flexible so can be wrapped around cylinders for imaginative lighting designs, or supplied in ridged mounts.  These custom polyester bandpass filters cover the visible spectrum.  Typical applications are in displays to protect from unwanted ambient light, and theatre lighting.

The colour effects within kodak wratten colour filters are achieved using organic dyes in a gelatine material, which is not possible in colour glass.  Wratten filters were originally designed for use in photography but are also used in imaging applications from industrial manufacture to medical.  Whilst less robust than polyester filter, their spectral data is more accurately documented.  The new range of kodak wratten 2 filters are now replacing older type wratten 1 filters which are manufactured using a ridged polymer. Wratten 2 filters are more robust and unaffected by water and moisture as gelatine type.  Wratten colour filters have a wide range of characteristics available and the sheets can easily be cut in the laboratory. Custom wratten colour filters area available in 300x100mm sheets to supply bespoke custom shapes and sizes to your specific requirements.  Typical applications are in displays to protect from unwanted ambient light, and a wide range of scientific instrumentation.

Custom linear variable filters:  Knight Optical is able to supply custom linear variable bandpass filters for use at the typical wavelengths, namely: 300nm to 800nm.  The variable filter is a combination of one long pass linearly variable filter, one short pass linearly variable filter, and a slit or aperture to select the mechanical bandwidth, which must be wider than the required optical bandwidth.  This combination of the filters and aperture allow for the unit to block and pass targeted wavelengths.  These can act, for example, as a laser line filter.  Individually the edge filters have a variable wavelength at the transition edge from transmission to blocking and from blocking to transmission, depending on the edge filter being a short or long pass type.  The figure here is an image of a typical filter arrangement showing the centre wavelength and the pass bandwidth.

Also, the individual edge pass and edge block filters are shown.  The filters are made to order and can be assembled into a custom kits.

Custom fluorescence bandpass filters:  Knight Optical can supply custom fluorescence bandpass filters that are specifically designed for use in fluorescence microscopy, spectroscopy, clinical chemistry, and other life science measurements.  The filters can have a centre wavelength with a narrow 50% band width of less than 20nm and a peak transmission of greater than 90%.  Outside this pass-band the filter blocks from the UV to NIR with better than 6OD.  A range of mechanical size options are available as mounted or unmounted options. Our emission and excitation fluorescence filters are ring mounted for ease of handling and exchanging in systems where filter sets are switched.  Each filter is marked and sealed to maintain the interference stack properties.

Custom dichroic bandpass and band-blocking filters:  Dichroic filters split the light into two or three bands and reflect one or more and transmit the others. Used at zero incidence they are generally used to select light of one of the primary colours.  Both dichroic bandpass filters and dichroic band blocking filters are available as custom options.  A huge range of dichroic filter colours are available not listed as standard on our website.  These can be supplied on White float glass or borosilicate or equivalent substrates dependent on application.  For applications where high levels of heat are transmitted from light source borosilicate or equivalent is the best option.  We hold a wide range of stock in 450mm diameter substrates so can offer custom shapes and sizes at short notice. Custom dichroic filter wedges can be supplied to build custom filter wheels.

Our custom bandpass filters can be supplied in range of mounting options.  For example custom band pass filters can be supplied to screw directly onto tamron lenses which have a 25.5 thread on the front and similar custom solutions for lenses in fujinon range where no thread is provided.

Knight Optical supply high quality custom bandpass filters made to our exact specification.  Every component is individually tested on our Agilent Cary 5000 spectrometers fitted with a UMA device for testing filter materials and coatings in transmission and reflection at any given angle.  We also have a DRA device fitted for testing complex coatings.  Our Agilent 660 FTIR spectrometer is used for materials and coatings between 3.5µm and 45µm.  All tested by our highly skilled technicians in our state of art metrology lab to ensure all components meet our high quality standards.

Contact our multilingual technical sales team and discover how Knight Optical’s high quality custom optical bandpass filters and service can improve your instrumentation and supply chain experience.

Our 2022/2023 Catalogue

Inside Knight Optical’s catalogue you’ll find details of the industries we serve as well as the many other services we can offer. It also showcases hundreds of our most popular products, supported by useful technical information, to help you choose the right part for your application.
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