Astrodon Photometrics Johnson-Cousins Filter, 31mm Mounted, edge-blackened- B***_31R-200097 (2nd Quality Discount)

$226.00 $199.00

Out of stock

This individually serialized filter, B***_31R-200097, has been scored at 9.925 and has a 11.88% discount. Astrodon 2nd Quality filters are still covered by our warranty for longevity, but are otherwise sold “as is” and are not returnable.

Astrodon 2nd Quality Filters are sold at a discount. 2nd Quality Filters are individually evaluated and graded for edge chips, scratches, pinholes and inclusions according to the standards set below:

Edge Chips: Score 1 point for each edge chip. Score 1 additional point for each edge chip that extends into the filter more than 2mm from the edge.

Pin holes: Score 1 point for each pinhole. Score an additional point for each pinhole that is “large”.

Scratches: Score 1/2 point for each scratch.

Inclusions: Score 1/2 point for each inclusion.

Subtract the sum of the points from 100 and divide by 10. This is the filter score.

 

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SKU: B***_31R-200097 Category:

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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