The Japanese-made IDAS LPS-V4
is in our opinion the BEST Light Pollution Suppression filter for astro photography with DSLR, colour and mono CCD cameras.
Light pollution suppression (LPS) filters are designed to suppress the common emission 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).
Unlike other light pollution suppression filters, IDAS filters are specifically designed for balanced colour transmission using the IDAS unique Multi-Bandpass Technology (MBT) process. The balanced transmission allows colour photographs to be taken with minimal colour cast to broadband emission objects such as stars, galaxies and globular clusters.
Usually, this filter triples the possible exposure time, but the time necessary for emission line objects is barely lengthened.
Important features of the IDAS LPS-V4 filter
♦ Better suppression of stray light than with the LPS-P2 filter
♦ Transmits H-beta, [O III], C2 and H-alpha lines
♦ Suitable for trichromatic photographs of emission line objects
♦ Therefore especially suited for diffuse and planetary nebulae
♦ A 19 nm bandbpass H-alpha filter results from combining with a Schott RG610 or Kenko R1
♦ Suitable for comets (Swan bands)
♦ Suitable for visual use, as closer to UHC filters than to usual light pollution filters
♦ High-quality anti-reflective coating
♦ Scratchproof hard coating
♦ Absorption of urban stray light and night glow
Uses beyond DSLR and emission nebulae
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. The filter also blocks infrared so a separate IR blocking filter is not needed.
An application as H-alpha filter is also possible. Combine with a Kenko R1 or a Schott RG610, and you get a 19 nm bandpass H-alpha filter. This is not only important for CCD camera users, but also for amateur astronomers with an astro-modified (enhanced spectrum by removing or replacing the built-in blocking filter) DSLR.
Comets can also be anhanced, as the Swan bands at 511 nm and 514 nm are also transmitted. That is a big difference to many UHC filters.
Higher durablity and smaller tolerances
IDAS 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, reducing spectrum shifts down to +/-1nm from the +/-3 or 4 nm shift of standard coatings.