Light Pollution Suppression (LPS) Filters
Light pollution suppression (LPS) filters are designed to suppress the common mission lines generated by artificial lighting, yet allow the important nebula emission lines to pass, thus enhancing the contrast of astronomical objects, particularly emission nebulae (see filter plots to see the effect on light pollution emission bands). The most recently introduced version (D2) has a bandpass designed to cope with the increasing trend of society's switch to LED lighting.
Unlike other light pollution suppression filters, IDAS filters are specifically designed for balanced color transmission using the IDAS unique Multi-Bandpass Technology (MBT) process. The balanced transmission allows color photographs to be taken with minimal color cast to broadband emission objects such as stars, galaxies and globular clusters.
LPS 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. [ More about IDAS filter production]
CCD imaging can also benefit, because although CCD imagers can already shoot through light pollution to some extent, including an LPS filter to the setup gives an added (signal-to-noise) edge as shown in these CCD examples (comparison testing by G. Tomita in Tokyo).
Additional independent tests and reviews are available here:
Sky & Telescope Review - "Light Pollution Filters for Cameras" (June 2001).
Note, however, that light pollution suppression filters are not a perfect substitute for dark skies. Refer to our discussion of the limitations and common misconceptions about light pollution suppression filters.
In addition to blocking selected light pollution emission bands, IDAS filters block the range 700-1000nm to insure that silicon sensors are adequately blocked from unwanted IR.
Plots shown are measured responses of production filters.
LPS filters are available for 1-1/4" and 2" (48mm) eyepieces, as well as in numerous sizes to accomodate most popular camera lenses. Each filter lot is tested and a plot of the spectral response of the lot is provided with each filter (see filter plot sample).
Information on Older IDAS LPS Filters:
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