QSO model is the premium version of the IDAS LPS-D1 filter. Enhancements are:
a) 1.1 mm thick glass. (Standard ones are 2.5 mm thickness)
Modern camera lens and focal reducer designs are very sensitive to changes of optical distance and refraction by an extra glass in the optical train to the sensor. The thinner glass minimizes being affected by those two factors.
b) Precision machined frame.
The knife-edge top ring along with matte-finish taper shape design dramatically reduces ghost reflections from bright stars outside of the field of view.
New revised LPS-D1 design improves on the popular LPS-P2 filter by reducing reddish background cast, improving the color rendition for one-shot-color CCDs and modified DSLRs. The plot below shows the difference between the P2 and D1 filters.
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.
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. The IDAS filter maintains better color balance than other filters which have been designed for visual use.
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.