Photometric filter Astrodon UVBRI Filter Rc 1.25" Rc 1.25" filter

Photometric filter Astrodon UVBRI Filter Rc 1.25".

UVBRI filters have been the standard for photometric measurements for decades. They have evolved over time as technology changed. H. Johnson in the 1950s and AWJ Cousins in the 1970s designed these filters for photomultiplier tubes (PMTs). M. Bessell in the early 1990s selected colored lenses to match the Johnson/Cousins designs for CCD cameras of the time. However, Bessell's designs were based on colored lenses available at the time. Some of those lenses (e.g., Schott KG-4 used in conjunction with Schott RG-9 to make the photometric "I" filter have been discontinued. Finally, PMTs went beyond 900 nm, while modern CCDs are sensitive to 1100 nm. Therefore, to truly match the Johnson/Cousins Ic filter, a dielectric coating must be used to block light beyond 900 nm in CCD systems. This cannot be achieved with colored crystals. Astrodon uses Ic and Rc (c = Cousins) to designate matching the Johnson / Cousins designs with the coated filters.

The Astrodon Photometrics UVBRcIc filters achieve the highest possible transmission for fainter objects:

• Use durable hard oxide coatings (no V-filter fogging) for durability
• Include A/R coating and construction that minimizes halos around stars
• Do not rely on discontinued colored lenses
• Includes Ic filter (which must use a 900 nm cut-off coating)
• With the advent of high performance, resistive and durable dielectric coatings, high transmission greater than 95% and durability can be achieved. Filters last longer and transmit more light. Durability is critical for consistent long-term research

Photometric filter Astrodon UVBRI Filter Rc 1.25".