2nd Quality Astrodon Sloan Filters
Astrodon filters are known for the highest of quality and perfection. Some of our filters don't make the cut to be sold in our premium line, however they are still excellent by normal standards and we are offering them here at a discount.
Please keep in mind that even though we have "rejected" these filters they still exceed industry standard for optical filters. Have confidence that these filters will still produce the same high quality images as our other filters even though they have a minor imperfection.
These filters are offered at 50% list price and are limited to stock on hand. Returns will only be accepted if the filter is in exactly the same condition we sent it. We photograph each filter in transmission and reflection as part of our QC process and images are retained for reference. A 25% re-stocking fee will be assessed for returns.
We have very limited stock on Sloan and if your selected filter is in stock you should purchase immediately. The rest of the Astrodon Sloan filters are on long term backorder and demand far exceeds supply. We are no longer taking additional backorders. We do not expect more photometric filters until June 2021 or later. We are working to get them faster.
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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). 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. A summary of the 50% points is provided in the chart below.