Astrodon Photometrics Sloan Filters



Earn up to 550 FarPoints.

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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.

You may click the “Get an alert” button to be notified when an out of stock filter is back in stock. 

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.”




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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.



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What’s in the box?

Photometrics Sloan Filter

Photometrics Sloan Filter Wavelength Graphs

Astrodon Sloan Filter Scans

Sloan Filter Comparison

Photometrics Sloan Filter 50% Points Chart

Sloan Details

  • 50% transmission points provided above (+/- 3nm typical)
  • Peak transmission guaranteed > 95%  (>90% for u’)
  • <=0.03%Tabs out-of-band 300 – 1100 nm
  • Single striae-free fused silica substrates
  • 1/4-wave propagated wavefront prior to coating
  • <0.5 arcminute substrate parallelism
  • 3.000 +/-0.025 mm substrate thickness prior to coating
  • 1.25″ mounted, 49.7 mm diameter and square unmounted standard sizes
  • Other sizes up to 150 mm square on a custom basis (see below)
  • Proud supplier to Las Cumbres Observatory Global Telescopes, AAVSO, Caltech/Palomar, MIT, Harvard, MacDonald Observatory, and other research organizations and universities worldwide
  • Proudly made in the U.S.A.



Substrate:                     3.0mm +/-0.025mm fused silica

Filter Size:                    25.4mm +/-0.1mm diameter

Clear Aperture:             Central 23.4mm diameter minimum

TWF:                           </= 1/4 lambda per any 25mm square area before coating

Parallelism:                   </=0.5 arcminute before coating

Coating:                        To edge of part

AOI:                            0 degree

Scratches:                     </= 0.06mm width; no limit on length

Particles/Bubbles:         </= 0.4mm dia.

Pinholes/Voids:             </= 0.2mm dia.

Edge Finish:                  As fabricated

Chips:                           </=0.5mm

Edge Treatment:           Edges blackened with Enthone M-0-N black epoxy ink.

Thickness </= 0.1mm. It may extend 0.5mm onto top and bottom surfaces.