CFW-8A Color Filter Wheel Manual
SBIG - Santa Barbara Instrument Group
2002 Santa Barbara Instrument Group 147-A Castilian Drive Santa Barbara, CA 93117 Telephone (805) 571-7244 FAX (805) 571-1147
Copyright Notice This manual is copyrighted by Santa Barbara Instrument Group (SBIG). This manual may not be copied in whole or in part.
CFW-8A Manual Version 1.4 Printed 2002

TABLE OF CONTENTS

Introduction....1 Overview of Taking and Processing Color Images..2 Telescope Work...2 Color Image Processing...3 Hardware Reference...4 Making the Electrical Connection...7 Maintenance of the Color Filter Wheel..12

SBIG CFW-8

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INTRODUCTION

SANTA BARBARA INSTRUMENT GROUP The CFW-8A Color Filter Wheel
This manual describes Santa Barbara Instrument Group's CFW-8A Color Filter Wheel. This product can be used with CCDOPS or CCDSoftV5 software to facilitate taking and processing of tri-color images with most SBIG cameras, including the ST-4X, ST-5, ST-6, ST-7, ST-8, ST-9 and ST-10 Imaging Cameras. This list may be expanded as we add new models. Many third party software packages also support SBIG products. The Color Filter Wheel is an accessory that mounts on the front of the camera. The filter wheel has five filter positions: Red Filter, Green Filter, Blue Filter, Clear Filter and 1 Clear Aperture position for additional filters of your choice. "Primary" color images are taken through the Red, Green and Blue Filters and the Clear Filter allows ordinary observing without having to refocus.

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SANTA BARBARA INSTRUMENT GROUP
Overview of Taking and Processing Color Images
This section provides an overview of the steps necessary, both at the telescope and in front of the computer, to take and process tri-color images.

Telescope Work

At the telescope you use the standard CCDOPS software to take sets of three images for each object. The three images represent the Red, Green and Blue primary images. Take these images as you would for monochromatic images except use the filter wheel to select each of the three primary spectral bands. You can take equal duration exposures in the Red, Green, or Blue or match the exposure duration of each primary image to the brightness of the object. Typical ratios of Red : Green : Blue are 1 : 1 : 1.6 to match the exposure to the CCD's sensitivity although accurate color balance should be done for your system with neutral grey objects or "white" G5 type stars. Each of these images should be dark subtracted1 and should be saved with a name that indicates the color of the filter (e.g., M51R, M51G, M51B). Note, however, that different software programs may handle tri-color files differently and the naming convention you use is dictated by your software. If you are using a fast system (low F number) and your images show signs of vignetting (such as a variation in the sky background level) then you should also take flat
You may also want to use the other image enhancement features of CCDOPS such as removing cool pixels. In general the three image set should be made to look their best prior to merging the RGB image. Page 2
field images and flat field correct your primary images using CCDOPS. Whether you need to take different flat field images for each primary color or not will depend on how different the vignetting pattern is for the different primary images. Typically a single flat field image will suffice.

Color Image Processing

A complete description of color processing is beyond the scope of this manual. A complete description and step by step instructions may be found in the CCDSoftV5 manual. Different software packages may handle the combining differently, but in general, you register or co-align the primary color images. You select the Red image from the set of three primary images you want to register and the software then loads and displays it. In that image you select a reference star (or pixel) and this rerence star (or pixel) is used to register the Red, Green and Blue images to one another. Once the images have been registered, they are merged together to form a tri-color image and minor adjustments are made to achieve color balance. Third party software packages such as Maxim DL, Adobe Photoshop or Aldus Photostyler are popular programs for combining the three primary images. While these packages tend to be expensive, often times you can find last year's versions at a sharp discount and they really are powerful image processing packages producing the most professional results.

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Hardware Reference
This section describes the CFW-8A Color Filter Wheel accessory for the ST-4X, ST-5, ST-6, ST-7, ST-8, ST-9 & ST-10 CCD Cameras. It includes instructions on how to install and operate the filter wheel.
Attaching to the CCD Camera
The CFW-8A is an accessory that allows the user to take images through optical filters. It is installed onto the camera and sits between the Optical Head and the Telescope. CFW-8

CCD Camera

Telescope
The filter wheel contains a magazine with five filter positions capable 1 of holding standard threaded 1 inch eyepiece filters. SBIG provides 4 four filters for use with the CFW-8A. There is a set of Red, Green and Blue interference filters for color imaging, and a Clear Filter which allows imaging "full spectrum" without having to refocus. No IR blocking filter is needed as the RGB filter have an IR blocking coating. The RGB filters have been selected for a specific bandpass so accurate red, green and blue images can be created. SBIG CFW-8 Page 4
The filter wheel attaches to other accessories through the universal T-Thread. The front and back of the CFW-8A have female T-Thread receptacles. Using T-Thread makes the CFW-8A a "plug and 1 play" system. You can attach a 1 inch or 2 inch nosepiece draw tube 4 into the front or you can attach an adapter that mates directly to the back of SCTs, replacing the standard Visual Back. the CFW-8A to the various model SBIG Cameras. ST-4X/ST-5 Users ST-4X and ST-5 users slip a TR-4 T-Thread adapter over the camera's nosepiece and screw the CFW-8A into the end of the TR-4 with the T-Thread coupler at the back of the CFW-8A. Refer to the Appropriate Section below for specific instructions on how to connect
ST-4X ST-5 TR-4 ST-6 Users
ST-6 users mount their camera to the CFW-8A by replacing the ST-6's removable nosepiece with a T-Thread flange. The CFW-8A is then screwed into the T -Thread flange with the T -Thread coupler. Proper clocking of the CFW-8A to the ST-6 is achieved by loosening the three set screws on the edge of the T-Thread flange, rotating the CFW8A, then re-tightening the three set screws.

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T-Thread Flange ST-7/ST-8/9/10 Users A permanent mounting of the CFW-8A to the ST-7/8/9/10 is accomplished by attaching the CFW8 directly to the face plate of the camera by the following procedure: 1. Remove the ST-7/8/9/10's T -Thread mount held in place with 4 phillips head screws and set the screws aside. [The TThread mount is where the nose piece screws into the camera head. It is a block approximately thick and shaped like the letter D attached to the face plate of the camera. It has three set screws holding an internal ring that has female TThreads]. 2. 3. Remove the cover of the CFW-8A and pull the filter magazine out of the housing. Remove the four rubber hole plugs from the rear of the CFW8A by pushing them through the housing with a small allen tool. Save these in case you decide to later use the CFW-8A with the T-Thread coupler or with a different camera. 4. Using the four 4-40 by 3/16 socket screws provided, attach the CFW-8A to the front of the ST-7/8. Make sure you use the provided screws whose length of 3/16 is required to

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SBIG the ST-7Sfront plate withoutINSTRUMENT GROUP ANTA BARBARA thread into breaking through the
blind taps. Alternate temporary attachment of CFW8 to ST-7/8/9/10 ST-7/8/9/10 users may also mount their camera to the CFW8A by unscrewing the camera's T-Thread nosepiece and screwing the Filter wheel onto the camera with an optional male-to-male T-Thread coupler. Proper clocking of the CFW-8A relative to the camera is achieved by loosening three set-screws at the font of the camera rotating the CFW-8A into position then re tightening the 3 set screws.

ST-7/8

Making the Electrical Connection
The CFW-8A has a cable that comes out the side that needs to connect to your camera electronics. The CFW-8A gets it power and positioning information from the camera thru this connector. If you're using an ST-4X, ST-5 or ST-6 the CFW-8A is supplied with a 15 foot cable that you plug into the AUX port on the camera's CPU. The AUX port is the 9 pin connector adjacent to the COM port you use for communicating with the PC. If you're using an ST-7/8/9/10 the CFW-8A is provided with a short cable that plugs into the cameras 9-pin telescope connector adjacent to the cable connecting the ST-7/8/9/10 to the PC.

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SBIG the CFW-8A connector has the phone-jack connector SANTA BARBARA INSTRUMENT GROUP Additionally,
that allows you to connect to the telescope for tracking and Self Guiding. If you ever decide to connect the CFW-8A to an ST-4X, ST-5 or ST-6 you can buy a 15 foot 9 pin extension cable to extend the short cable back down to those cameras' CPU.
Attaching to the Telescope
At the front of the CFW-8A you can attach any T-Thread based adapter that will connect to your telescope, including the nosepiece from your camera. When using a nosepiece to slip the camera and filter wheel assembly into an eyepiece holder, you need to pay careful attention to insure the weight of the filter wheel with the camera attached is held in place with the eyepiece holder's retaining screws. SBIG also sells an optional T-Thread Visual Back Adapter which screws directly onto the back end of the popular Schmidt-Cassegrain telescopes. This makes for a very rigid mounting. After attaching the camera/filter wheel combination to the telescope, you should t hen drape the Camera's head cable over the fork of the telescope and clip it in place so that the cable doesn't drag on the ground as the telescope rotates. Also avoid hanging the camera head and filter wheel by the cables as this could overly strain the cables.

Positioning the Filter Wheel
The motorized CFW-8A filter wheel is positioned using commands in the CCDOPS software's Filter menu. The unit does not require calibration like the older CFW-6A and is auto-homing at power-up.
You need to tell the CCDOPS software that you are using the CFW8A and this is accomplished by selecting the CFW-8A as the filter SBIG CFW-8 Page 8
SBIG the Setup commandBof the FilterNSTRUMENT GROUP SANTA ARBARA I wheel type in menu. If you have an
older version of CCDOPS that does not show the CFW-8A you can still use the CFW-8A by first erasing the FILTER.CFG file in the CCDOPS directory (the software will create a new one for you) then select the CFW-6A type filter wheel in the Setup command. There are individual commands in the Filter menu with hot-keys for positioning the flter wheel. Also the Camera Status window i shows which filter is currently in position, and this information is recorded with images when they are captured. You can rename the filters using the Filter Setup command. If you have removed the filter wheel from your camera or removed the filter from the magazine you can select the None command in the Filter menu. The None command doesn't position the filter wheel, it just tells the software that you aren't using a filter at the moment. If you run without filters for a period of time you should use the Filter Setup command to select the "None" type of filter wheel.
Remote Shutter Operation with the ST-4X and ST-5
ST-4X and ST-5 users can use the CFW-8A as a remote shutter for taking dark frames. If you cover-up the fifth position in the filter wheel (or any other position for that matter) with some sort of opaque material (a sandwich of aluminum foil between layers of black construction paper works well) you can tell the CCDOPS Version 3 and later software to use that darkened position to cover the CCD for taking dark frames rather than continually asking you to cover and uncover the telescope.
Use the Setup command in the Filter menu to tell the CCDOPS software which filter position has been darkened by setting the Dark position item. Select which of the five filter position you want to use for "Light" frames using the positioning commands in the Filter menu SBIG CFW-8 Page 9
SBIGcomes to taking a darkARBARA INSTRUMENT GROUP SANTA B and when it frame the software will position
the filter wheel at the dark position, take the dark frame, then reposition the filter back to where it was for the light frame, All this without you having to cover the telescope!

Vignetting

The increased length of the filter wheel assembly will cause vignetting for fast systems (those with low F numbers such as F/3.3). The vignetting will be worse for the ST-8, ST-9 andST-10 with their relatively large CCDs versus the ST-7. Vignetting will show up as a fall off in the sky background at the edges of the field of view. Flat fielding greatly reduces the troublesome effects of vignetting. ST-8/9/10 users should use a 2 inch nosepiece or should connect the CFW-8A to the telescope through the T -Mount directly so as to 1 avoid vignetting caused by the 1 inch nosepieces. 4

Selection of Color Filters
SBIG color filters include an infrared blocking coating so that a separate IR blocking filter is not needed. The filters used in the SBIG filter wheel have been chosen to optimize the accuracy of the colors produced by the tri-color software. The passbands of each filter are summarized in the table below:
Color Filter Passbands Filter Red Green Blue SBIG CFW-8 Passband (nm) 612-670 488-574 392-508 Page 10
SBIG are custom filtersARBARA INSTRUMENTfor ROUP SANTA B G The filters designed specifically SBIG
cameras. Dichroic filters were chosen over absorption filters for three reasons. First of all, they have high transmission in the passband region. Second, a sharp transition can be obtained in the region around 496 nm. And last, they are all deposited on a sheet of glass of the same thickness, eliminating focus shifts due to varying filter thickness. An infrared blocking coating is applied to these filters to eliminate spectral leaks in the infrared where the CCD has high sensitivity. These bands would be severely contaminated if these leaks were not blocked. Colored plastic filters also have severe red leaks beyond the visible spectral range, so one should particularly avoid those. The sharp transition between the blue and green region is necessary for proper color rendition of emission sources. The 500 nm oxygen line is blue-green in color, and so must pass through both blue and green filters. The hydrogen-beta line at 486 nm is very blue, and must be rejected by the green filter. The green filter will pass less than 10% of this line.

Hints for the User

Be aware that color imaging is substantially more difficult than using the CCD unfiltered. Whereas before, you only needed to take one image you now need to take three, and each one needs to be about 4 times as long since only a portion of the total spectral range is passed by each filter. This aggravates tracking problems, which are also more pronounced due to the requirement of registering
three images. Hot pixels and cosmic ray hits are more objectionable since they become strongly colored in the final image (the hot pixel remove utility in CCDOPS should be used). In spite of all this, you will find that even subtle colors present in galactic scenes enhance the SBIG CFW-8 Page 11
SBIG and emission nebulas take onNSTRUMENT GofROUP SANTA BARBARA I image noticeably, beautiful hues blue,
blue-green and red. Star colors are dramatically enhanced, and impart a three dimensional aspect to the image. We have endeavored to create a product that enables true color pictures of deep sky objects to be produced. We have made certain philosophical decisions with which some may disagree. For example, if we traveled in space to where we were quite close to the Dumbbell Nebula it would appear to be a large gray mass devoid of color, buried in mostly white stars. If we traveled to other galaxies they would be no brighter, in general, than our Milky Way. Many extended objects, such as the Horsehead Nebula, have very low contrast relative to the sky background, often less than 10%, and would never stand out sharply. The images you see on the computer screen are not true, in the general sense, being considerably enhanced in brightness and contrast over the actual object. We have carried this philosophy to the way our program displays star images; stars saturate to the proper color, not white. impression. Your eye would see them differently but less accurately! We find the result very pleasing, but please give us your

Maintenance of the Color Filter Wheel
The surface of the filters may be safely cleaned with Isopropyl or Methyl alcohol and cotton swabs. Use a gentle circular motion, using several swabs until the surface is clean. The machined parts may be cleaned by rubbing with a soft cloth. A small amount of lubricant can be applied to the magazine axle should the unit start to chatter but please do so sparingly. It really is a light duty interface. If some part of the CFW-8A assembly is damaged, replacement parts may be obtained from Santa Barbara Instrument Group. Disassembly of the CFW-8A is rather straight-forward. You can remove the front cover by removing the six screws that hold it in SBIG CFW-8 Page 12
SBIGremoved, theANTA cover comesINSTRUMENT Gof the S BARBARA ROUP place. Once front completely free
CFW-8A allowing access to the filter magazine. The filter magazine can be removed by lifting the magazine straight-up out of the back housing by one-quarter inch then tilting away from the motor and removed completely from the housing. Upon inspection you will notice that the filter magazine has a top and a bottom. The filters screw in from the bottom and the top has the optical alignment pins. As viewed from the top the filter positions are shown in the figure below, noting the position of the double-pinned position adjacent to position 3: 5
Top View of the Filter Magazine The filter wheel is reassembled in the reverse process. Rotate the filter magazine so that the alignment pins straddle to either side of the motor then tilt the magazine into place and drop it into the back of the housing. Be careful to not bend the axle in the process and
also make sure the magazine is inserted with the filters down towards the camera) and the alignment pins up. The filter wheel will be held in place against the motor and can be leveled to make installing the front cover easier. Though it SBIG CFW-8 Page 13
SBIG necessary toANTAyou may loosen the two screws that S BARBARA INSTRUMENT GROUP should not be do so
hold the motor in place. If you do so you'll need to remove the motor cover from the font cover so that you can readjust the tension of the motor against the magazine. Adjust the tension till the magazine does not rotate freely but not so tight as to put strain on the motor that would be accompanied by irregular movement of the magazine or soft "clicking" sounds. You do not need to worry about the angular orientation of the magazine as the unit will auto home itself upon power-up.

MODEL CFW-9 COLOR FILTER WHEEL
SBIG pioneered tricolor imaging for amateurs by developing hardware and software to register and color balance Red, Green, and Blue images that display spectral emission of deep space objects. When interference filters are carefully selected to match the spectral regions of ionized gases the images taken through the filters can be summed together to represent the distribution of these gases. Tricolor images are taken through the CFW-9 Color Filter Wheel and processed with CCDOPS, CCDSoftV5, or third party software. The primary color Model CFW-9 Color Filter Wheel images are taken through Red, Green and Blue filters. After the images are taken they are processed with the software to co-align the Red, Green and Blue images. The co-aligned image is then color balanced on the computer monitor to become a tricolor RGB image, which can then be saved to disk. A similar process is used to make LRGB images except that a greyscale luminance image is added for detail. CCDOPS software also allows the user to perform image processing functions such as smoothing and sharpening as well as saving images in TIFF format. The raw images can also be saved in a variety of formats for export to any of the many commercially available software programs for color image processing such as Maxim DL and Photoshop.
The CFW-9 system is designed to be "direct connected" to any ST-7/8/9/10/2000 imaging camera for a thinner, more rigid mounting. An optional male-to-male t-thread adapter is also available allowing easier (but less rigid) attachment and detachment for occasional use. On the front end a variety of optional T-Thread accessories are available including 1.25 inch and 2 inch diameter nose pieces as well as a "Visual Back Adaptor" for direct connection to SCT's. A new optional accessory is the AO-8 which in fully compatible with the CFW9 filter wheel's I2C accessory port and the I2C accessory port on all ST cameras with USB. The CFW-9 is operated through the CCDOPS software and utilizes a closed loop stepper motor system with positional accuracy of 0.01 inches. It holds up to five standard 1.25" diameter thread-in filters. It is available with Red, Green, and Blue (RGB) interference filter sets and a clear filter CFW-9 Attached to an (focusing). The new SBIG RGB filters also block Infrared "ST" Series Camera (IR) so an inline IR Blocking filter is no longer required. These filters are mounted in standard size cells that normally fit into 1.25" eyepiece barrels. The CFW-9 adds back focus of approximately 1 inch. Although some examples of tricolor imaging are shown in this catalog it is difficult to display the wide range of techniques that our customers have developed. The CFW-8 can produce photographic quality tricolor images that rival color astrophotographs. However, these RGB images also contain an entirely new and added level of valuable information; the identification and
distribution of different ionized gasses in an object. SBIG also furnishes precision UBVRI filter sets with the Model CFW-9, filters that allow the user to perform color photometry to measure the classification and temperature of objects.

Red Image

Green Image

Blue Image

Combined Image
Note: The three separate Red Green and Blue CCD images are not identical. Each one displays only the spectral region that the filter allows to pass. Since each filter corresponds to a known spectral region the combined image displays the distribution of those ionized gases.
THE RGB PROCESS IN THREE SIMPLE STEPS
1. Using the CFW-8 and CCDOPS software take three images, one each though the Red, Green,and Blue filters respectively. 2. Using CCDOPS, CCDSoftV5 or third party software, register the three images and color balance them on the computer monitor. 3. Combine the RGB files to create a tricolor image.
Model CFW10 and CFW10-SA Filter Wheel
The new CFW10 is a tenposition filter wheel designed for the USB version of our ST camera series or any camera where a serial port is available for controlling the wheel. The CFW10 accepts control input via either the I2C port or the RS232 serial port. When attached to an STCFW-10 Ten-position Filter Wheel 7/8/9/10/2000 USB camera, the filter wheel receives power and control commands through the I2C accessory port of the camera - no additional power or cable to the computer is required. The stand-alone version, CFW10-SA, is for use with other cameras, the filter wheel is controlled via an RS232 serial port and is powered by an external 12VDC power supply. The filter slots are threaded for standard 1.25" filters. The portion of the housing between the camera and the telescope is only about 3/4" (20mm) thick for minimum back focus. Two versions of the housing make it possible to use the CFW10 either as a separate unit, or as an integral piece replacing the face-plate of the ST series camera. The replacement version contains a high quality optical window with superior AR coatings. By using the filter wheel housing as a replacement face plate for the camera, an additional 1/4" (6mm) in back focus is eliminated and normal 35mm camera lenses may be used with the filter wheel in place. The front aperture of the CFW10 contains standard t-threads. A custom camera lens adapter will be available for commonly available 35mm Nikon, Canon, Olympus and other lenses. For attachment to the telescope, a 1.25" nosepiece (shown) or 2" nosepiece may be used, or a t-thread to visual back adapter for more secure fit to Schmidt-Cassegrain scopes. For other scopes, any adapter with male t-threads can be used to secure the filter wheel. The CFW10 will be offered in addition to the CFW8A as an option for any ST series camera. It should be noted, however, that the CFW10 will not work with

older parallel cameras unless one has an available serial port on the computer to control the CFW10 through a separate serial cable.
CFW10 Exploded View - Thickness is approximately 0.6" when attached to camera in lieu of the camera's face plate, and approximately 0.76" when attached over the camera's face plate. CFW10 cover is removed for access to filters without opening the camera cavity in either configuration.
Filters for RGB and LRGB Color Imaging, Narrow Band Imaging and Photometry
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.
50mm RGB Filters for the STL Series Cameras
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! 1.25" Filters:
Custom Scientific RGBC Filter Set Custom Scientific H-alpha Filters Custom Scientific UBVRI Filter Sets

1.25" Filters

Astrodon LRGBCH-a Filter Set Astrodon H-alpha, [O-III], [SII] Filters Baader UV / IR Blocking (Luminance) Filter

50mm Filters:

Custom Scientific LRGBC Filter Set Custom Scientific H-alpha Filters Custom Scientific UBVRI Filter Sets
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 described 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. In the case of the Astrodon filters, where the goal was equal exposure times, there is a different set for cameras using interline CCDs and those using full frame CCDs due to the different response curves of the two types of CCD. One benefit of the Astrodon filters is that they are parfocal with Astrodon narrow band filters and the full set of LRGBCH-a [OIII] [SII] can be used in our CFW10 tenposition filter wheel without having to refocus between filter changes.

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 astro-imagers 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.
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.
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.

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.
Astrodon 1.25" LRGBC plus Narrowband Filter Sets
This "expanded" color imaging set from Astrodon is a new entry for SBIG. In May of 2005 we began delivering our new CFW10 ten-position filter wheel for the ST-7/8/9/10/2000 cameras. This filter wheel lets the user put a variety of filters in the carousel and not worry about which ones might be needed at a given time. For maximum flexibility both a Luminance and a Clear filter are included in the Astrodon sets. A parfocal H-alpha filter rounds out the expanded set. Many imagers prefer to take H-alpha images along with RGB images and combine them using the H-alpha frame as one color channel or as the luminance layer. This process of capturing H-alpha at the same time as the rest of the RGB frames is made much easier if the process can be automated. Astrodon filters, RGB and narrow band, are all parfocal. This eliminates the need to refocus between any filter, even the H-alpha filter, when automatically capturing a sequence of images and it makes them ideal sets for the larger 10 position filter wheel. Individual narrow band, [O-III] and [SII] can be added later, or a "Super Set" can be ordered that includes all 8 filters. These are also parfocal with the rest of the Astrodon line. SBIG offers two sets of Astrodon filters: A 6 piece "Expanded" Color set consisting of LRGBCHa, and an 8 piece "Super Set" consisting of: LRGBCHa [O-III] [SII]. These Astrodon filters are currently available from SBIG only in 1.25" size. The "E" series is designed for the ST-7/8/9/10E/ME cameras, and the "I" series is designed for the ST-2000XM camera.
Astrodon 1.25" Narrowband Filters
The three narrow band Astrodon filters included in the "Super Set" are [O-III] (500.3 nm), H-alpha (656.3 nm), and [SII] (680.nm). These passbands are chosen by amateurs most often because of the abundance of emission nebula containing some or all of these emission lines. Narrow band filters are designed to pass

the emission line wavelength while rejecting other wavelengths outside the filters passband. This makes them very effective at suppressing light pollution. Some imagers restrict their imaging to only these narrow bands, assigning a "color" (R,G and B) to each filter in order to create a false color image. The most famous example of such a false color image is probably the Hubble Space Telescope's "Pillars of Creation." Each of these narrow band filters has a 6 nm passband, and each is parfocal with the other Astrodon RGB filters.
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.
BAADER NARROWBAND FILTERS SBIG is pleased to offer a custom set of Baader narrowband filters for the ST and STL cameras effective as of this announcement. SBIG and Baader Planetarium, Mamendorf, Germany, have enjoyed a longstanding relationship. Some accessories for the ST and STL cameras have been made by Baader for SBIG over the years, including the UV/IR cut filter that we supply with every single-shot color camera for optimum color balance. Now, this relationship translates into incredible savings for SBIG customers. Baader Planetarium has developed a set of narrowband filters in in 1.25" and 2" sizes. The 2" filter is specifically made for the STL series cameras in the 50.8mm (2" unmounted) size for the STL filter carousel. These drop in both the 5 position and 8 position filter wheels for the maximum clear aperture in a 2" filter for our large 11000 CCDs. Moreover, these new narrowband filters are the same thickness as our standard 50.8mm LRGBC set making them all parfocal for the STL models. Each filter is made of high quality substrate, polished to yield 1/4 wave flatness or better, with hard multiple antireflection coatings on both sides. The narrowband filters are available in a 7nm wide H-alpha filter, 8nm wide Hbeta filter, 8nm wide OIII, and 8.5nm wide SII. In addition, there are some specialty filters such as an IR pass filter and a U filter ("Venus" filter). The narrowband filters typically have around 90% peak transmission at the design wavelength. These filters are also available in 1.25" sizes for ST series cameras, in threaded cells for the CFW8A, CFW9 and CFW10 filter wheels. Note, however, that due to the different thickness of the smaller 1.25" RGBC filters the narrowband filters are not parfocal in the smaller size at this time. The remarkable news is that a set of the 3 most commonly used narrowband filters (H-alpha, OIII, SII) is available for under $400 for the ST cameras (1.25" size), and under $900 for the STL camera (50.8mm size)!

The IR-Pass filter blocks wavelengths below 670 nm. At these longer wavelengths, planetary images are less disturbed by wavefront distortions in the atmosphere. By combining a luminance image taken with the IR-Pass filter, along with RGB frames, overall image sharpness is significantly enhanced. Some of the world's best amateur planetary images have been taken with this technique. This filter is available only in 2" OD threaded cell (48mm threads). The latest coating technologies permit the Baader U Filter (Venus Filter) to transmit from 300nm to 400nm, with a peak transmission of 80%! The filter completely blocks the rest of the region from 200nm to 1500nm, through the use of a complex 20 layer dielectric coating stack, on top of a special UG-11 substrate. Up till now, Amateur efforts typically relied upon deep violet colored filters, or combinations with simpler interference filters, which do not provide the high transmission and efficient rejection outside the important spectral region from 320nm to 390nm. Given the poor transmissions of many optics in the UV and the lower sensitivity of some CCDs to this wavelength, high filter efficiency and complete rejection at longer wavelengths becomes paramount to recording good contrast at reasonable exposures. The same high optical quality and features as the other Baader filters ensures the highest contrast and sharpest images possible. Interestingly, the solar Calcium K-Line is also within the pass band of this filter. This opens up the exciting possibility
for recording flare structures on the solar disk or edges. This filter is available only in 2" OD threaded cell (48mm threads Baader's innovative new designs and features, together with the very latest thin film coating technologies, result in outstanding performance, efficiency, and image quality. Baader filters are unique, in that they utilize true optically polished flat substrates. Ultra-thin precision cells deliver the maximum clear aperture and minimize vignetting. Ion beam hardened coatings ensure your filter will withstand real-world use and repeated cleaning - they are tough enough to survive boiling water! Baader Planetarium filters are made from striae-free substrates, and actually fine optically polished flat to within 1/4 wave p-v over the entire surface, plane parallel to within 30 seconds of arc. This important and unique custom step adds cost - but the result is a filter that maintains the full wavefront quality of the telescope without double images or ghosting, even at high magnifications. Critical to maintaining this level of flatness are Baader's carefully balanced coating designs, which prevent coating surface stresses from warping the substrate. Such high flatness enables Baader filters to be used far in front of the focal plane, ahead of star diagonals. Durability has always been a hallmark of Baader Planetarium. The multi-layer dielectric coatings are plasma assisted and Ion beam hardened using the latest technology (the coatings are harder than the glass substrate itself!). Baader filters withstand repeated real-world exposure to the elements and physical cleaning. Users need not leave their precious filters dull and dust encrusted to avoid cleaning - Baader filters may be used and cleaned without fear. Baader Filters will truly last lifetimes. Baader's special filter cell design offers unique features that enhance their reliability and usability. Though difficult to produce, the ultra-thin filter cell results in the maximum possible clear aperture, in order to minimize vignetting (1" Filter clear aperture is 27mm!). The special threading has been designed to fit the wide variety of eyepieces and accessories (there is significant variation between the 1 filter threading used by eyepiece and accessory manufacturers). The front 'crown' of the filter incorporates milled notches which make handling and threading the filter a more secure operation in the dark.

Despite the high quality and advanced technology, Baader Planetarium filters are affordable. By leveraging high volumes across all filters in the Baader family, these filters can be offered at very reasonable prices.