Astrodon Gen2 LRGB E-Series and I-Series Tru-Balance Filters
Astrodon Narrowband Filters
Astrodon NIR Luminance Filters
Astrodon Photometrics UVBRI Filters
Astrodon Exo-Planet Filter
Astrodon makes the best performing, most durable filters for astrophotography and research.
All Astrodon astrophotography filters are manufactured in the U.S. with superb quality control using 100% hard-oxide sputtered coatings. You pay extra for Astrodon filters because you expect and receive all the benefits that our highest performance and great durability provides. You have invested considerable time and money in your telescope system and filters are a critical part of that system. They are the "spark plugs" that make the "engine" go. Step up to Astrodon filters and see the difference yourself.
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.
The 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. This saves you precious imaging time and thus, simplifies your imaging.
The I-Series filters are designed to approximately equalize the flux of Interline CCD detectors (formerly Kodak), including compensation for the solar photon flux. The I-Series filters compensate for the lower red response of these Interline detectors affecting the design of the Green and Red filters. The Luminance and Blue filters are the same as those in their E-Series. 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. This saves you precious imaging time and thus, simplifies your imaging.
Astrodon Narrowband filters set a new bar of performance and durability for imaging and research. The narrow 5nm and 3nm bandwidths enhance contrast of emission targets by lowering your background signal. The guaranteed >90% transmittance at the emission wavelength provides you with the highest signal available. This guaranty is expensive to manufacture for such spectrally narrow filters, but it assures you in writing on each filter box that you will get what you paid for. These two factors combine to provide you with the highest contrast available. Astrodon's latest narrowband filters are typically achieving >95-98% transmittance. Astrodon Narrowband filters are renowned for minimizing halos around bright stars, even for long exposures of 30-45 minutes typical of narrowband imaging in astrophotography. Lastly, Astrodon Narrowband filters are coated to the edge of the part and are edge blackened. This is critical to minimize stray light for a filter that blocks most light except for the narrow bandpass.
Astrodon Narrowband filters for imaging are all about contrast. Contrast brings out faint features by reducing the background - the narrower the filter, the better. The problem is keeping the signal (%T at the emission line) constant as the filter becomes spectrally narrower. This is why Astrodon's >90%T guarantee is so important, even though it becomes very costly to manufacture. But, this assures you that you can take advantage of the improved contrast with our narrower filters compared to the much less expensive 7nm - 8.5nm filters on the market.
Astrodon Narrowband filters currently are provided off-the-shelf for:
Bandwidth it is spectral width of the transmission region at 50% of the peak transmittance - full width at half maximum.
UVBRI filters have been the standard for photometric measurements for decades. They have evolved over time as technology changed. H. Johnson in the 1950s and A.W.J. Cousins in the 1970s designed these filters for photomultiplier tubes (PMT). M. Bessell in the early 1990s selected colored glasses to match the Johnson/Cousins designs for CCD cameras of the time. However, Bessell's designs were based upon colored glasses available at the time. Some of those glasses (e.g. Schott KG-4 used in conjunction with Schott RG-9 to make the "I" photometric filter have been discontinued. Lastly, PMTs of the time limited light past 900 nm, whereas modern CCDs are sensitive to 1100 nm. Thus, to truly match the Johnson/Cousins Ic filter, a dielectric coating must be used to block light past 900 nm for CCD systems. This cannot be achieved with colored glasses. We use Ic and Rc (c = Cousins) to designate that we match the Johnson/Cousins designs with our coated filters, as closely as possible.
Astrodon Photometrics UVBRcIc:
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 300nm to the sensitivity limit of silicon CCD cameras near 1100nm. They combined colored glass filters and short-pass dielectric coatings to steepen the low wavelength side of the bandpass. The [O I] 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 the 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.