Lumicon Dust Seals keep dust, moisture and insects out of your Schmidt-Cassegrain telescope (SCT). The glass is a plane-parallel polished surface that passes more than 98% of all visible wavelengths, with no noticeable reflection or aberration. The LF3155 threads onto male SCT rear-cell threads (2" x 24 tpi), and presents the same threads for accessory attachment.
This Lumicon filter has a clear aperture of 42.8mm (1.7") - the largest available clear aperture on the market for a filter of this kind. Item weight = 2 oz.