We have very limited stock on Johnson-Cousins filters and if your selected filter is in stock you should purchase immediately. The rest of the Astrodon Johnson-Cousins filters are on long term backorder and demand far exceeds supply. We are no longer taking additional backorders.
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Standard sizes are 1.25", 31mm, 50mm round, and 50mm square. The 1.25" is 27.5 mm of filter glass mounted in a 1.25" filter cell. The 31mm is 27.5mm of filter glass mounted in a 31mm ring. More information here:
Unlike other Astrodon filters, the Photometric filters (Johnson-Cousins and Sloan) do not come as 36mm of unmounted glass. For those who want 36mm round for use in a 36mm filter wheel, 27.5 mm of filter glass can be mounted in our 36mm adapter. More information on 36mm mount here:
We also have a limited quantity of 12mm and 25mm (call for pricing and availability).
100%-Coated for long-term durability and consistency of research with the highest throughput.

Astrodon Photometrics U, B, V, Rc, Ic:
- Achieve the highest transmission possible for fainter objects
- Use hard-oxide durable coatings (no V filter fogging) for durability
- Include A/R coating and construction that minimizes halos around stars
- Do not depend upon colored glasses being discontinued
- Includes Ic filter (which must use a 900 nm cut-off coating)
- Proud supplier to Las Cumbres Observatory Global Telescopes, AAVSO, Caltech/Palomar, NASA, MIT, Harvard, Apache Point, U. Valencia, and research organizations worldwide
- Proudly made in the U.S.A.
Internal absorption of light in colored glasses used to make traditional filters limits the final throughput. For example, the traditional UV filter made with colored glasses typically does not transmit more than 60-70% at the peak. The Rs filter, 70 -80%. Astrodon Photometrics 100%-coated filters exceed 95% (see actual scans below).
Schott BG-39 glass (with Schott GG-495 glass) used in the traditional photometric V filter may degrade and become cloudy due to surface crystallization from exposure to humidity. It needs to be covered by a clear glass to protect any exposed surface, making the filter thicker.
With the advent of high performance, hard and durable dielectric coatings, both high transmission in excess of 95% and durability can be achieved. Filters last longer and transmit more light. Durability is critical for long-term, consistent research.
Astrodon Photometrics U, B, V, Rc, Ic filters adhere to the Johnson/Cousins/Bessel designs as closely as possible. The following is a spectral compilation of actual scans of the Astrodon Photometrics UBRcIc filter set.
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