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MidOpt filters
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Longpass Colour Filters

Longpass filters let longer visible and infrared wavelengths pass while blocking the shorter ones. Useful for improving contrast, resolution and separating colors in black/white or colour applications. Typically not recommended for machine vision unless blocking of multiple wavelengths is necessary.




LP500– Yellow Longpass – blocks most blue and UV wavelengths
Model
Transmission
Suitable for
LP500
Passes 500nm and above
Absorbs 480nm and below
• Increasing contrast and resolution in monochrome cameras


Colour longpass filters are used with monochrome cameras to aid in increased contrast and resolution. As the name implies, these filters block UV and shorter visible wavelengths, and pass longer wavelengths of light. Except in those few cases where an IR blocking or other shortpass filter is incorporated into the camera/sensor, for the most part, the use of a broad colour bandpass filters (whose designs incorporate these longpass filters) over these color longpass filters alone.

The reason for this is that colour filters are usually specified for use with similar monochromatic LED or laser diode colors in order to block ambient light. When looking at the spectral response of most CCD/CMOS camera sensors, it can be seen that they typically have excellent deep red and near-infrared sensitivity. When super-imposing any longpass filter's transmittance curve over a camera's spectral response curve, approximately half or more of the unwanted ambient light – all of the longer wavelength light – is not being blocked by the longpass filter.

In comparative testing where the difference between a longpass and a bandpass filter may not seem to be dramatic, the bandpass filter will also provide insurance for what might happen at some point in the future. By blocking almost all of the unwanted light, the effects of any change in ambient or introduced lighting that often occur at a later date can be nullified. Instead of an LP500 filter, an alternative choice might be a BP525 filter.

While bandpass filters are more popular than longpass filters, Longpass colour filters are still available for customers who are more familiar with them and continue to request them.



LP515 – Yellow-Orange Longpass – blocks all blue and UV
Model
Transmission
Suitable for
LP515
Passes 510nm and above
Absorbs 500nm and below
• Increasing contrast and resolution in monochrome cameras


Colour longpass filters are used with monochrome cameras to aid in increased contrast and resolution. These filters block UV and shorter visible wavelengths, and pass longer wavelengths of light. Except in those few cases where an IR blocking or other shortpass filter is incorporated into the camera/sensor, for the most part, the use of a broad colour bandpass filters (whose designs incorporate these longpass filters) over these color longpass filters alone.

The The reason for this is that colour filters are usually specified for use with similar monochromatic LED or laser diode colors in order to block ambient light. When looking at the spectral response of most CCD/CMOS camera sensors, it can be seen that they typically have excellent deep red and near-infrared sensitivity. When super-imposing any longpass filter's transmittance curve over a camera's spectral response curve, t approximately half or more of the unwanted ambient light – all of the longer wavelength light – is not being blocked by the longpass filter.

In comparative testing where the difference between a longpass and a bandpass filter may not seem to be dramatic, the bandpass filter will also provide insurance for what might happen at some point in the future. By blocking almost all of the unwanted light, the effects of any change in ambient or introduced lighting that often occur at a later date can be nullified. Instead of an LP515 filter, an alternative choice might be a BP535 filter

While bandpass filters are more popular than longpass filters, Longpass colour filters are still available for customers who are more familiar with them and continue to request them.

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