Astrodon Photometrics Sloan Filter, 50mm Round- r'2_50R-200034 (2nd Quality Discount)
This individually serialized filter, r'2_50R-200034, has been scored at 9.9 and has a 12.50% 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.
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). All Astrodon Photometric filters are 100%-Coated for long-term durability and consistency of research with the highest throughput.
NOTE: In Astrodon part numbers we pronounce the ‘ character (apostrophe) as “prime” and the _ character (underscore) we pronounce as “sub.” So u’2_27R should be read as “u prime 2 sub 27 R
The Sloan Digital Sky Survery (SDSS) filters were designed by Fukugita et al. (Ast. J., 411/4, April 1996, p. 1748-1756) to include five mostly non-overlapping filters covering 300 nm to the sensitivity limit of silicon CCD cameras near 1100 nm. They combined colored glass filters and short-pass dielectric coatings to steepen the low wavelength side of the bandpass. The sky glow line at 557.7 nm occurs between the g’ and r’ filters, and thus is reduced.
The SDSS photometric system is the most common filter set used today. The Hubble Space Telescope is equipped with an SDSS set that provides a large reference database for research. Much of photometry up to magnitude 23 will be done in this system with meter-class telescopes. The upcoming large collaborative survey projects (Large Synoptic Survey Telescope – LSST; Panoramic Survey Telescope and Rapid Response System – Pan-Starrs) will also use SDSS filters.
Astrodon Photometrics Sloan Filters have evolved to our current Generation 2 filters with technical input from Las Cumbres Observatory Global Telescope Network (LCOGT) and others. Additional separation was included between the g’ and r’ filters to better avoid atmospheric sky glow . In particular the Y and z_s near-infrared filters were added to ensure that the filter, and not the detector, controlled the high-wavelength cut-off. This in contrast to our z’ filter, which is simply a cut-on, or long-pass filter. Lastly, out-of-band blocking was tightened from an average to absolute specification to further minimize the already small leakage.