astrodon - 50mm dia. Unmounted u Filter

The Sloan Digital Sky Survey (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 [O I] skyline at 557.7 nm occurs between the g' and r' filters, and is thus 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. 

The following is a summary of the 50% transmission points of a variety of SDSS filters from the Large
Filter Consortium. The new Astrodon Photometrics Sloan set is included for comparison.

The Astrodon Photometrics Sloan filters use only dielectric coatings to achieve steep cut-on and
cut-offs and peak transmissions in excess of 95%.

 
WIYN
DES
LSST
Pan-Starrs
Fukugita
Astrodon
u'
 
 
 
 
 
320/385
g'
402/550
400/550
402/552
402/552
410/551
401/550
r'
560/710
560/710
552/691
552/691
556/695
555/695
i'
700/820
700/850
690/819
691/818
690/814
690/820
z'
830/980
830/1000
818/922
818/922
841/982
820/-

To minimize  internal reflections that produce halos around brighter stars, the entire bandpass and
blocking layers are deposited on one side of the substrate and a high-quality broadband anti-reflective
coating is placed on the other side.

These filters are parfocal with all Astrodon LRGB and narrowband filters.

Specifications:

    * 50% transmission points provided above (+/- 3nm typical)
    * Peak transmission guaranteed > 95%  (>90% for u')
    * <0.1%T out-of-band 300 - 1100 nm
    * Striae-free, single fused silica substrates
    * 1/4-wave propagated wavefront prior to coating
    * <0.5 arcminute substrate parallelism
    * 3.000 +/-0.025 mm substrate thickness
    * 1.25" mounted
    * 49.7 mm dia. unmounted
    * 49.7 x 49.7 mm square unmounted