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Astrodon Photometric Sloan Gen2 U Filter - 320/385 nm - 1.25" Threaded Cell - U2-27R

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SKU: ASD-U2-27R

About Astrodon Gen2 Sloan 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 Sloan Photometric filters are fully coated without colored glass. Featuring the highest throughputs on the market, these filters are able to improve signals and enhance faint night sky objects.

Astrodon Gen2 Sloan Photometric Filters - Additional Information

Originally designed to include five predominantly non-overlapping filters that cover the spectrum from 300 nm up to the sensitivity limit of silicon CCD cameras around 1100 nm, Sloan Digital Sky Survey (SDSS) filters steepen the low wavelength side of the bandpass by combining colored glass filters with short-pass dielectric coatings. The skyglow line at 557.7 nm is reduced as it exists between the "G" and "R" filters.

SDSS photometric filter sets are the most common filter system in current use. In order to facilitate a large reference database for research, the Hubble Space Telescope is outfitted with an SDSS filter set. This system in conjunction with meter-class telescopes will accomplish much of photometry up to magnitude 23. Upcoming large collaborative survey projects such as the Large Synoptic Survey Telescope - LSST, and Panoramic Survey Telescope and Rapid Response System - Pan-Starrs, will also employ the SDSS filter system.

Using technical contributions from Las Cumbres Observatory Global Telescope Network (LCOGT) among others, Astrodon has taken their Photometric Sloan Filters to the next level. With these Generation 2 Filters, more separation is included between the "G" and "R" filters for greater avoidance of atmospheric skyglow. Unlike the Astrodon "Z" filter, a mere cut-on or long-pass filter, the "Y" and "Z-S" filters were added for the specific purpose of assuring that the high wavelength cut-off is controlled by the filter and not the detector. Finally, leakage already at a minimum is further reduced by tightened out-of-band blocking form average to absolute specification.

Astrodon Gen2 Sloan Filter Highlights

  • Provides 50% transmission points (+/- 3 nm typical)
  • Maximum transmission assured over 95%
  • At most 0.03% tabs out-of-band from 300 nm to 1100 nm
  • Single striae-free fused silica substrate
  • 1/4-wave propagated wavefront prior to coating
  • <0.5 arcminute substrate parallelism
  • Substrate thickness is 3 mm +/- 0.025 mm before coating
  • Proudly manufactured in the USA


Astrodon 1.25" Gen2 Sloan U Filter

Edge-blackened round 1.25" threaded cell Astrodon Generation 2 Sloan "U" Filter featuring the highest possible throughput available. Designed from a single high quality 3 mm thick fused silica substrate using no colored glass, this Astrodon filter is fully coated for the consistency and long-term durability necessary for extended research projects. Provides transmittance for light in the 320 nm to 385 nm spectral region.

Astrodon Gen2 Sloan Filter Detailed Specifications

  • 3 mm +/- 0.025 mm fused silica substrate
  • 25.4 mm +/- 0.1 mm diameter filter size
  • Central 23.4 mm diameter minimum clear aperture
  • TWF: <= 1/4 lambda per any 25mm square area before coating
  • Coating to edge of part
  • AOI: 0º
  • Scratches: <= 0.06mm width; no limit on length
  • Particles/Bubbles: <= 0.4 mm diameter
  • Pinholes/Voids: <= 0.2 mm diameter
  • Edge finish as fabricated
  • Chips: <= 0.5 mm
  • Edge Treatment: Edge-blackened with Enthone M-0-N black epoxy ink
  • Thickness: <= 0.1 mm which may extend 0.5 mm onto top and bottom surfaces