Astrodon - Tru-Balance I-Series - 1.25" Mounted CRGB Filter

TRU-BALANCE FILTERS
SIMPLIFY YOUR IMAGING
Great Filters Just Got Better - Generation 2 Now Shipping!

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.

I-Series filters are designed to approximately equalize the flux of Kodak's Interline 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.

Introducing Generation 2 True-Balance filters (LRGB2) in April, 2008 in all sizes. This is the first change in Astrodon filter design and fabrication since their inception.  We listened to your requests. 

• 1.25" mounted and 49.7 mm diameter
• ~1:1:1 color combine weights for G2V white-point for Kodak Interline detectors
• Equal RGB exposures and one dark time
• Better color separation (spectra)
• Better color rendition of galaxies based upon color theory
• Significant reflection and star halo reduction (see Alnitak image)
• Enhanced contrast for HII regions in galaxies
• Small 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 filters  
• Striae-free 1/4 wave fused silica substrates
• 30 arcsec parallelism
• Ultra-hard and durable sputtered coatings
• Proudly made in the U.S.A.

         Astrodon Spectra

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. Please see the article on Parfocal and the Critical Focus Zone. 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.  Tony Hallas' image of M45 had NO touch-up or processing out of halos on those super bright stars. Not necessary with Generation 2 filters. There were NO halos to start with!

Generation 2 LRGB E-Series Testimonial from Tony Hallas (note - the I-Series uses the same high efficiency blue and luminance filters as the E-Series) :

M45 (no halos) (Click on image to enlarge)	M33 (HII definition) (Click on image to enlarge)

"I would like to take a minute to comment on the 50mm Gen II filters that I have installed in my Apogee 16803 camera. 

 Generation 2 LRGB Testimonial from R. Jay GaBany:

M106 (click for hi-res)