Filters for RGB and LRGB Color Imaging,
Narrow Band Imaging and Photometry

50mm RGB Filters for the STL Series Cameras

Many of the best astro images seen in Sky & Telescope and Astronomy magazine are taken with monochrome CCD cameras and color filters using RGB or LRGB combination techniques (L=luminance, R=red, G=green, B=blue, C=clear).   A luminance filter typically blocks UV and IR light, passing only the same wavelengths as the RGB filters.  A clear filter does not block UV or IR but is used for maximum signal transmission over the full range of the CCD.  By taking separate images through custom filters, and combining the results to make an RGB image, the full resolution of the CCD is utilized and a great deal of latitude is preserved for image processing.

In addition to traditional Red, Green and Blue filters, some astro imagers combine H-alpha with RGB to enhance the appearance of emission nebula.  Narrow band filters may also be used exclusively to create dramatic "Hubble like" false color images of emission nebula.  Some of the most beautiful images taken of large emission nebula are simple monochrome images taken through an H-alpha filter.  One of the benefits of narrow band imaging is that light pollution and sky glow is suppressed by the narrow band filters.  With the right filter, it is possible to capture detailed images of emission nebula from one's backyard in the middle of the city under the light of a full moon! 

Those studying variable stars and performing other photometric measurements use standardized UBVRI or BVI filter sets to record their observations.  These photometric filters have evolved over the years to provide results that are as close as possible to the measurement obtained with earlier instruments such as the photometer.

All of the filters listed below are of the best quality.  The RGB sets are dichroic filters designed for the highest transmission.   The passbands are carefully designed for SBIG cameras.  Our Custom Scientific RGB filter set is designed for excellent all around use with an accurate balance of emission sources and continuum light. 

Custom Scientific 1.25" RGBC 4 filter set:

This RGBC filter set is the standard SBIG set that comes with the CFW8A filter wheel and is intended for use with the ST-7/8/9/10/2000 cameras.   The set is also available separately.  It is designed to give a proper balance of continuum light from stars and proper ratios of H-alpha and [O-III] emission line sources (e.g., bright nebula and planetary nebula) at the same time.  These professional quality, high transmission, dichroic filters have been tested over time by some of the best astroimagers in the world.  Many of the remarkable images seen in the gallery of Sky & Telescope and Astronomy magazines have been taken with this filter set and an "ST" series camera.  The colored filters are parfocal, antireflection coated and IR blocked.  The clear filter is AR coated only.  Click here for current prices.

Custom Scientific 50mm LRGBC five filter set

This LRGBC five filter set for the STL series cameras is designed to drop into the STL filter carousel without vignetting the largest (35mm format) CCD in the series.  The STL carousel is threaded for 48mm ("2") filter cells as well, but the full 50 mm diameter of these filters provided the maximum aperture for the large format CCDs.   For this reason they are supplied without threaded cells.  Like the smaller Custom Scientific RGB filters, this 50 mm filter set is professional quality, antireflection coated, IR blocked.  The Luminance filter is UV and IR blocked to match the RGB cutoffs, it is also AR coated.  The clear filter is AR coated only.  Click here to see the luminance and clear filter transmission characteristics.   Click here for current prices.

Custom Scientific 1.25" and 50mm H-alpha Filters

SBIG offers two versions of H-alpha filter from Custom Scientific, a relatively narrow 4.5 nm filter and a wider 10 nm filter.  Both are available in either 1.25" size or 50 mm size.  The smaller 1.25" filter fits in the CFW8A or CFW10 filter wheel and is suitable for the ST-7/8/9/10/2000 cameras.  The 50mm size fits in the STL carousel and is suitable for any of the large format STL series cameras.  The benefit of the narrower 4.5nm filter is greater suppression of sky background and light pollution.  Very detailed images of faint H-alpha nebula can be faithfully captured even when imaging in heavily light polluted skies or under the glare of a full moon.  The 10nm filter is also very good at suppressing light pollution, but not quite as good as the narrower 4.5nm filter.   The 10nm filter is better for darker skies, and it is also less expensive than the 4.5nm filter. Click here to see the 10nm filter transmission characteristics.  Click here for current prices.

Custom Scientific 1.25" and 50mm UBVRI Photometric Filters

In the 1950's Harold Johnson (Yerkes and Macdonald Observatories) established three photometric bands, the U, B, and V based on the sensitivity of  the photomultiplier tube that he used at the time.  Later on he established red and infrared (R and I) bands using a PMT with enhanced red sensitivity.  In the mid-1970's, A.W.J. Cousins and John Menzies (South African Astronomical Observatory) used different filters, that when used with a newer, better detector, would reproduce the Johnson bands. Then, in the 1980's CCD detectors were beginning to replace the photomultipliers so a new set of filters was required that, when used with the CCD's would give the same results as the older filters when used with the PMT.  Bessell (Mt. Stromlo and Siding Spring Observatories in Australia) did this in 1990 (PASP, 102, 1990, 1181). It is Bessell's filter definitions that are the industry standard today when using CCD's.  These professional quality, polished, AR coated, photometric filters are available in both 1.25" and 50mm sizes.   Click here to see the individual filter transmission characteristics.  Click here for current prices.

Baader 1.25" UV / IR Blocking Filter

The Baader UV / IR blocking filter is essentially a luminance filter.  It is included with ST-2000XCM color cameras to improve the color balance of the single shot color CCD by blocking the near IR light.  It is shown here along side the optional T-ring with filter threads for use on any ST cameras.  It can be placed behind a camera lens adapter and used to block the out of focus near IR light that causes stars to look bloated with using a typical 35mm camera lens to shoot wide field images.  Click here for current prices.

Baader 1.25" and 50.8mm Narrowband Filters

Click here for information about the new Baader Narrowband Filters.

evised: May 07, 2008 04:03:43 PM.
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