Longpass filters do one clean job: they divide the spectrum at an edge and keep the long side. In a fluorescence instrument the longpass is the emission filter, rejecting the excitation light and passing the red-shifted signal; in a sensor it is the element that keeps visible glare out of an infrared measurement. The documented listing offers custom optical glass long pass filters across cut-on wavelengths from 680 nm to 1100 nm, spanning the deep-red and near-infrared.
Specifying a longpass means specifying the edge, not a band: the cut-on wavelength (conventionally where transmission reaches half its passband value), how deep the blocking must be below it, and how the edge behaves at your angle of incidence. The catalogue records the cut-on range of the documented longpass line, not its angle behaviour, so an instrument that uses the filter at an angle should state the angle in the enquiry. The quotation discussion settles which construction your edge steepness actually requires.
An enquiry for this line carries five inputs: the cut-on wavelength the layout needs, the shortest wavelength the blocking must cover and the depth it must reach, the passband range the detector actually uses, the angle at which the filter will sit in the instrument, and the clear aperture and substrate size the holder expects. With those five stated, the confirmation answers against the recorded range and your layout, not against a generic edge description.
Documented Longpass Listing
| Listing (storefront) | Documented detail |
|---|---|
| Custom optical glass long pass filters | Cut-on wavelengths 680 nm to 1100 nm |
| Family position | Long-pass family inside the documented filter group, alongside bandpass, shortpass and notch |
In a fluorescence set, the longpass is one element among several: an excitation bandpass filter before the sample, a dichroic mirror to fold the path, and the longpass in front of the detector. The elements are ordered against one wavelength plan in the enquiry, and each element is confirmed item by item in the quotation. Note that the documented longpass listing carries an unusually high listed minimum quantity; the minimum for your specification is confirmed in the written quotation, so ask rather than assume.
Frequently Asked Questions
What cut-on wavelengths are available?
The documented custom range spans 680 nm to 1100 nm cut-on wavelengths.
Longpass or bandpass for a fluorescence emission channel?
Longpass when everything above the edge is signal; bandpass when only part of that range is wanted and the rest is background. The selection guide on this site compares the two.
What is the minimum order?
The storefront listing shows an unusually high minimum for this line; the applicable minimum for your cut-on and size is confirmed in the quotation.
Edge Steepness and the Absorptive Alternative
One specification choice deserves attention: whether the longpass edge is made by a coating or by the glass itself. The catalogue does not record which construction stands behind a given longpass listing, so the construction question belongs in the enquiry. The documented line on this site is custom optical glass long pass filters across a 680–1100 nm cut-on range, and the enquiry is the place to state the edge steepness the layout needs, so the construction can be matched to it rather than defaulted.
Request a Quotation
Tell us the component, material, dimensions and coating you need. Pricing and lead time for your specification are confirmed in the written quotation.