IDAS Type 4 BGR+L filter sets are designed for tri-color (BGR) or quad-color (BGR+L) imaging, with special attention to features which address accurate rendition of colors as viewed by the human eye:
All filters utilize the unique IDAS Ion Gun Assisted Deposition (IGAD*) coating technology for superior coating durability (quartz hardness) and safer cleaning. IGAD coatings also improve temperature and humidity stability of the filter performance, reducing spectrum shifts down to +/-1nm from the +/-3 or 4nm shift of standard coatings.
The unique bandpass arrangements of the IDAS Type 4 filters allow several types of imaging to be done with combinations of filters:
Conventional BGR+L imaging is accomplished by using the IR blocking L filter in conjunction with each of the component color filters (BGR). The Clear filter is used for the L-component so that the focus position is the same as for each of the other components.
Near IR (NIR) "tri-color" (false color) imaging can be done by using an optional IR-pass / visual cutoff filter (R700) in conjunction with the BGR and clear filters. Note that the imaging sensor and optics must also be capable of imaging IR wavelengths.
NIR imaging also allows for better "penetration" of areas dominated by interstellar dust due to the reduced scattering of longer wavelengths. The Trapezium region of M42 is a good example of an area benefitting from NIR imaging.
Full-band False Color imaging can be done by using the BGR and clear filters without additional filtering. This allows IR-capable imaging chips to utilize their full spectral capability. Note that the imaging optics must also be capable of properly imaging IR wavelengths.