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Astrodon Photometric Johnson-Cousins Rc Filter - 1.25" Threaded Cell - RC-27R
About Astrodon Johnson-Cousins UVBRI Filters
Astrodon filters are high performing, durable filters that provide significant aid for astrophotography and research pursuits. Each filter is constructed using a highly innovative process with a single high quality 3 mm thick fused silica substrate and full hard oxide sputtered coatings. Optimally equipped to provide consistency for long-term research undertakings, Astrodon UVBRI Photometric filters are fully coated and use no colored glass. Featuring the highest throughputs on the market, these filters are able to improve signals and enhance faint detail in deep sky objects.
Astrodon Photometric UVBRI Filters Highlights
- Provides the highest possible transmission for fainter targets
- Contains hard-oxide coatings with no V filter fogging for added durability
- A/R coating and construction is included to reduce halos around stars
- Does not rely upon discontinued colored glass
- Includes Ic (the c is for Cousins) filter with required 900 nm cut-off coatings
- Proudly manufactured in the USA
Astrodon Johnson-Cousins UVBRI Filters - Additional Information
For decades, UVBRI filters have been the standard against which all other photometric filters are measured. Over the years, these filters have adapted to ever changing technology. Originally designed for photomultiplier tubes (PMT) by H. Johnson in the 1950s and A.W.J. Cousins in the 1970s, by the early 1990s, colored glass needed to be selected that would correlate to then current Johnson-Cousins CCD camera models. However, due to the fact that older PMTs limited light past 900 nm while newer CCD models are sensitive to 1100 nm, these filters must feature dielectric coatings that adhere to modern CCD systems by blocking light past 900 nm. In addition, colored glass cannot be used because some of those glasses used back in the 1990s have been discontinued in the interim.With colored glasses, internal light absorption previously made the limits of traditional filters the final throughput. For instance, a traditional UV filter made using colored glasses normally does not have a peak transmission of more than 60-70%. Meanwhile, transmittance for fully coated Astrodon Photometrics filters exceeds 95%. The introduction of hard, durable, and highly efficient dielectric coatings have made over 95% peak transmission as well as stability for consistent extended research possible. Compared to earlier versions, these filters have a longer lifespan while transmitting more light.