Astrodon Generation 2 (Gen2) Tru-Balance RGB filters have revolutionized CCD imaging. Their popularity is due to their ease-of-use, high optical throughput and great resulting colors 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 red-sensitive full-frame (formerly Kodak 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% for equal length exposures. This can never be perfect, but it does allow you to take one exposure time for all of your RGB data and therefore, only just one corresponding dark exposure time. Again, this saves you precious imaging time and thus, simplifies your imaging.
- Set includes Luminance (NIR/UV-blocked colorless), Red, Green and Blue filters
- 1.25" mounted, 31, 36, 49.7 mm dia, 49.7 mm square (36 mm filters will not exceed 36.1 mm dia.)
- 3 +/-0.025 mm single 1/4-wave fused silica substrate before coating
- 30 arcsec parallelism
- ~1:1:1 color combine weights for G2V white-point for Full-Frame (E) detectors
- Best choice for back-thinned and Sony detectors
- Equal RGB exposures and one dark time
- Better color separation (see spectra)
- Better color rendition for galaxies based upon color theory
- Significant reflection and star halo reduction
- Enhanced contrast for HII regions in galaxies due to narrower red (not orange) filter
- Spectral "gap" between green and red filters to minimize effect of light pollution, especially from high pressure sodium street lamps (see spectra)
- Highest efficiency blue filter with less UV
- Correct "teal" OIII color for planetary nebula (OIII signal >97% in blue and green)
- Parfocal with Astrodon's high-performance narrowband, Clear and Near-IR Luminance filters
- Ultra-hard and durable sputtered coatings coated to the edge of each filter
- Proudly made in the U.S.A.
The E-Series filters were designed for cameras containing the full-frame KAF8300, KAF3200, KAF6303, KAF16803 sensors. They are also a good choice for the latest Sony and back-thinned sensor. The E-Series red filter is a deep red filter about 60 nm wide, which excludes much of the light pollution from high pressure sodium street lamps. Other filter suppliers try to "force fit" their orange filter (designed for the interline KAI11000, KAI2000 sensors) for use with these full-frame sensors. Their orange filter (see below) is about twice as wide spectrally as our deep red filter. As a result, their orange filter tends to "wash out" HII regions in galaxies and detail in nebula. Their blue and green color weights are no longer balanced and as a result, the OIII color in planetary nebula is skewed strongly toward blue, rather than the correct teal color. These are the reasons why Astrodon designed E- and I-Series filters for these different classes of cameras for optimum results.