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Astrodon Photometric Johnson-Cousins Ic Filter - 1.25" Threaded Cell - IC-27R

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SKU: ASD-IC-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

UVBRI filters have long set the standard for photometric measurements. As technology has evolved, so have these filters. In the early 1990s, following initial designs in the 1950s by H.Johnson, and the 1970s by A.W.J. Cousins for photomultipler tubes (PMT), these filters needed to have colored glass selected for them that would match Johnson-Cousins CCD camera designs of the period. But since some of those glasses have been discontinued in the interim, colored glass cannot be used. And since modern CCDs are sensitive to 1100 nm as opposed PMTs of the time that restricted light over 900 nm, it is essential that the dielectric coating used blocks light past 900 nm for modern CCD systems.

Internal light absorption in colored glasses once meant the final throughput would be dictated by the limits of traditional filters. Take the UV filter for example. Maximum transmission for a traditional UV filter designed using colored glasses typically does not exceed 60-70%. In contrast, Astrodon Photometrics filters with 100% coatings top 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.