astrodon - Tru-Balance E-Series - 50mm dia. CRGB Filter

Astrodon Tru-Balance RGB filters have revolutionized CCD imaging. Their popularity is due to ease-of-use, high optical throughput and great resulting color for galaxies, star clusters and nebulae. There are two varieties of Tru-Balance filters - E-Series and I-Series.

E-Series filters are designed to approximately equalize the flux of Kodak's full-frame (E-Series) CCD detectors,
including compensation for the solar photon flux. This means that your RGB color combine weights will be approximately 1:1:1
within perhaps 10%.  This can never be perfect, but it does allow you to take equal time exposures for your RGB data and also just
one corresponding dark exposure time.

    *  1.25" mounted, 50 mm dia., 50 mm square
    * ~1:1:1 color combine weights for G2V white-point for Kodak Full-Frame (E) detectors(patent pending)
    * Best choice for backthinned and Sony detectors
    * Equal RGB exposures and one dark time
    * Better color separation (spectra)
    * Better color rendition for galaxies based upon color theory
    * Significant reflection and star halo reduction (see Alnitak image)
    * Enhanced contrast for HII regions in galaxies
    * Spectral "gap" to minimize effect of light pollution
    * Highest efficiency blue filter with less UV
    * Correct "teal" OIII color for planetary nebula
    * More parfocal  - thickness 3+/-0.025 mm*
    * Parfocal with Astrodon's high-performance narrowband and near-IR filters  
    * Striae-free 1/4 wave fused silica substrates
    * 30 arcsec parallelism
    * Ultra-hard and durable sputtered coatings

Astrodon filters are known for being parfocal on most systems.  The new thickness tolerance of +/-0.025mm (25 microns) for
Generation 2 LRGB fitlers is a factor of 2 better than Gerneration 1 filters, and should be parfocal for systems down to f/3.5, IF
your optical system is well color corrected. We have reduced the UV contribution in the lumincance and blue filters for this
reason to reduce star bloat  The Clear (no near-IR blocking) may produce bloated stars if your optical system has poor near-IR
focus.   Use the near-IR-blocked Luminance filter in this case. The Clear filter is likely a better choice for reflectors, such as
Ritchey-Cretiens, rather than refractors or camera lenses.

Halo elimination results from a pioneering design that places both the bandpass layer and the blocking layer on one side of the
1/4-wave substrate and a high performance anti-reflective coating on the other side.  As a result there is virtually no internal
reflection between these surfaces that can cause halos around bright stars in other filter brands.  M45 is one of the most
demanding of targets that often leads to halos around bright stars.