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The ST-4000XCM is a special limited addition to the "ST" line of self-guiding cameras. It uses a large 4.2 megapixel KAI-4020CM
color CCD previously available only in an STL camera body. This CCD has 2048 x 2048 pixels at 7.4 microns square. This is the
same size CCD used in the STL-4020 camera. The KAI-4020CM comes in a single class without column defects. The KODAK DIGITAL
SCIENCE KAI-4020CM is a high-performance multi-megapixel image sensor designed for a wide range of scientific, medical imaging,
and machine vision applications. The 7.4 mm square pixels with microlenses provide high sensitivity. The vertical overflow drain
structure provides antiblooming protection, and enables electronic shuttering for precise exposure control to 0.001 seconds.
Other features include low read noise, low dark current, negligible lag and low smear. This CCD uses a high gain output amplifier
that reduces the read noise by almost half compared to previous versions. Our preliminary tests of this CCD installed in
prototype ST camera body exhibits a read noise of less than 8e- rms and a dark current of less than 0.1e- at 0 degrees C. The
KAI-4020CM CCD is a progressive scan detector with an active image area of 15.2 x 15.2 mm.
Features:
* The largest CCD available in an ST series camera - 100% larger than the ST-2000XCM
* Single-Shot Color CCD with 300X antiblooming protection
* 4.2 million pixels: 2,048 x 2,048 at 7.4 microns
* High resolution on smaller telescopes with 7.4 micron square pixels
* Built-in TC-237H autoguider for self-guiding
* External self-guiding with the optional Remote Guide Head containing a TC-237H CCD
* Mechanical shutter for automatic dark frames
* Electronic shutter for exposure times to 0.001 second
* Good sensitivity
* Low read noise
* Low dark current
* Thermoelectric cooling with air only or with water circulation
* Fast downloads - 10 seconds for a high resolution full frame image, 2 seconds for quarter frame
* Professional software
* Easy to use
* Full compliment of optional custom accessories
* Low price
* SBIG quality and support
his generous 4.2 Megpaixel CCD is twice the size as the KAI-2020CM used in the ST-2000XCM camera. It is approximately 50% larger
than the KAF-3200ME CCD used in the ST-10XME. With a diagonal measurement of ~21.5mm, it is the largest CCD currently available
in the ST series camera body. Because of the size of the sensor package, this camera is only available in single-shot color in
the ST body, without filter wheel. For monochrome with 2" filters, there is no significant savings over the STL model that
includes a 2" filter wheel. SBIG has made a special buy of CCDs for this camera and the low price we are offering on the
ST-4000XCM is limited by the supply of CCDs we have on hand. It is a substantial supply, but once they are gone this special will
end.
The ST-4000XCM camera comes with a built-in, custom designed, MAR coated, UV+IR blocking filter for optimum color balance in
astronomical imaging and improved performance with camera lenses and short fast refractors. The characteristics of this custom
filter are essentially the same as the separate Baader UV+IR blocking filter ("Luminance Filter") that we include with other
single-shot color cameras. Since no external UV/IR blocking filter is required, using a camera lens is a simple matter of
attaching a lens adapter. The built-in UV+IR filter helps shape the red cut-off but does not significantly attenuate the
important wavelengths of H-alpha and [SII]. The UV+IR filter has better than 97% transmission at H-alpha. Additionally, the
transmission curves of the RGB filters on the CCD itself happen to place the mostly unwanted wavelength of Sodium light pollution
in the minimum gap between the red and green filters while passing H-alpha and [SII]. The peak red transmission is around 525nm.
By way of comparison, typical unmodified DSLR cameras tend to have peak red transmission around 600nm with a significant fall off
at H-alpha and almost no response to [SII]. This means that the DSLR is roughly twice as sensitive to Sodium light pollution as
it is to H-alpha. The opposite is true for the ST-4000XCM where the curve of the red filter attenuates the Sodium line and
transmits twice as much light near H-alpha (See charts below).
The ST-4000XCM supports the optional Remote Guiding Head and is fully compatible with the new AO-8 Adaptive Optics accessory.
It has the standard ST camera heat exchanger with water cooling capability. With both a mechanical and electronic shutter, the
ST-4000XCM can automatically take dark frames as needed with exposure times from 0.001 seconds to 1 hour. Self-guiding is
possible with either the built-in TC-237H CCD or the optional Remote Guide Head with external TC-237H CCD.
A Natural Step-Up From a DSLR
We are sometimes asked by DSLR users considering moving up to a dedicated astronomical CCD camera what benefits they will get in
one of our Astronomical CCD cameras compared to a less expensive consumer digital camera. The answer, simply, is sensitivity and
performance. So what makes an astronomical CCD camera more sensitive and a better performer" The paragraphs below briefly
address the various factors that answer this question:
1. Sensitivity
DSLRs are designed to take pictures of terrestrial scenes in daylight conditions where there is typically plenty of natural light
or artificial light provided by the photographer. Contrast, brightness and dynamic range in the scenes are high. Exposures are
usually very short, fractions of a second up to several seconds. The noise inherent in the camera is generally not much of an
issue because terrestrial scenes provide plenty of signal compared to any camera noise. Some consumer cameras have gone a step
further and include a "noise reduction" mode where a dark frame is subtracted or other processing steps are taken in the camera to
reduce unacceptable levels of noise for dark scenes that require longer exposures. Even with this enhancement, however, consumer
digital cameras are generally limited to exposures of a few minutes before camera noise becomes a problem when used for astronomy.
Astronomical CCD cameras are designed from the beginning to take pictures of very faint objects at night against a dark
background, the proverbial black cat in a coal bin. There is no possibility of adding artificial light to brighten the scene.
Contrast, brightness and dynamic range are typically very low. Often, the objects are only a few percent brighter than the
background. Light from the object is at a premium and single exposures up to an hour long are possible. The camera electronics
are designed from the first step to the last to contribute as little noise to an image as possible within certain practical
limits. The dominant source of noise from the camera in long exposures however is dark current in the CCD itself. This is
thermally generated charge that can only be reduced by cooling the sensor.
Others have compared the sensitivity of cameras based on Kodak CCDs to the sensitivity of popular Canon and Nikon DSLR cameras.
Johannes Schedler, known for his excellent DSLR astro images, compared the sensitivity of the STL-11000M camera to his Canon 10D
and found the STL-11000M to be about 4 times as sensitive. Christian Buil independently compared Canon 10D, Canon 20D and a Nikon
D70 DSLRs to a monochrome Kodak 0402ME based CCD camera and found the 0402ME significantly more sensitive. From the Quantum
Efficiency Curves of the KAI-4020M we see that the sensitivity of the KAI-4020M monochrome (and its smaller counterpart, the
KAI-2020) is slightly higher than the KAI-11000M. Taking this into account, and the effect of the color filters, it is fair to
conclude that the ST-4000XCM is more sensitive than a typical DSLR camera in blue and green wavelengths, and significantly more
sensitive in the red and H-alpha. The DSLR's deficiency in red sensitivity can be mitigated to a degree by modifying the camera
but even in these cases, exposures are still limited to around 10 minutes due to the dark current in the CCD or CMOS sensor. The
ST-4000XCM's thermoelectric cooling and low initial dark current allow the camera to expose an hour at at time, if desired and
conditions permit.
The first light image at right is a single, self-guided, 30 minute exposure taken through a TeleVue 4" f/5 refractor by Alan
Holmes while testing the guiding performance of the prototype ST-4000XCM camera. The image is reduced to 25% for display.
2. Cooling
In addition to quantum efficiency and spectral response, sensitivity to weak signal is improved as the noise from the camera is
reduced. In the case of the KAI-4020CM CCD the read noise is exceptionally low, typically around 8e- rms. The dark current is
also quite low, less than about 0.1 e- at 0 degrees C. DSLR camera manufacturers can take steps in their circuit designs to
reduce noise from their electronics, but there is little they can do in circuit design to lower the dark current (and therefore
the dark current noise) that is ever present in an image because dark current is a property of the CCD itself. Dark current in an
image increases in proportion to the length of the exposure. For terrestrial imaging, with short exposures, the dark current is
so small that it can usually be ignored. However, for the longer exposures needed for astronomical imaging, dark current is
typically the dominant source of noise from the camera. Fortunately, another characteristic of CCDs is that dark current
increases with temperature. Conversely, lowering the temperature of the device lowers the dark current. This is such an
important factor for astronomical imaging that virtually every good dedicated astronomical CCD camera made has some provision for
lowering the temperature of the CCD, even if it is just the addition of a heat sink to passively dissipate heat from the device.
The ST-4000XCM camera has built-in thermoelectric cooling that will reduce the temperature of the CCD significantly with air only
and even more with water circulation. The KAI-4020CM's dark current is reduced by 50% for every drop of ~ 6 degrees C. Cooling
the CCD by 30 to 40 degrees below ambient lowers the dark current by approximately 100X. This is but one significant advantage of
an astronomical CCD camera and a primary limitation with a consumer DSLR camera.
3. Self-Guiding
Longer exposures require guiding. The best images of dim deep space objects you will see are the result of relatively long
exposures, usually many minutes up to several hours total exposure time. Virtually every telescope mount made for amateur
astronomy requires guiding corrections during long exposures in order to prevent stars from appearing like streaks instead of
points. The need for this depends on the focal length one is using, the resolution desired in the final image, and the quality of
the mount. But in general, guiding is required for best results when imaging dim objects even with the best mounts. When imaging
with a DSLR, a separate guider may be added to accomplish this task. There is the added cost and complexity associated with this:
a separate guide scope, good mounting system and controlling two cameras at the same time. The ST-4000XCM camera, on the other
hand, has a second CCD built into the camera next to the imaging CCD. This TC-237H guiding CCD is 657 x 495 pixels at 7.4 microns
square. It is the same CCD that we previously used as the main CCD in the ST-237 camera and STV camera/autoguider. This guiding
CCD is controlled with the same software that controls the camera. There is nothing else to buy, no external cables or mounting
requirements, and since the built-in guiding CCD is looking through the same optical tube as the imaging CCD, it is the most
accurate way to guide a long exposure, particularly when imaging at a relatively long focal length. If desired, however, an
external guider is easy to add to the ST-4000XCM. Simply plug the optional Remote Guide Head into the ST-4000XCM and guiding can
be accomplished using a shorter focal length optical arrangement such as the eFinder. The guiding tests seen in the pair of
images above right were made with a mount intentionally set up with poor polar alignment in order to test the guiding capability
of the Remote Head and eFinder combination under less than ideal conditions. First an unguided 10 minute exposure was taken to
show the extent of the error (left), then self-guiding was turned on and a second 10 minute exposure was taken to determine how
well the error was corrected (right).
4. Adaptive Optics
The ST-4000XCM camera fully supports the AO-8 Adaptive Optics system. SBIG, in concert with Benoit Schillings and Brad Wallis,
introduced the first affordable Adaptive Optics system for imaging deep space objects with amateur's CCD cameras. This was the
AO-7. Since then, we have added a second generation AO-L for our Large Format cameras and the newest AO-8 replaces the older
AO-7. The AO-8 is controlled by the on-board guiding CCD in the camera, or by the external guiding CCD in the Remote Guide Head.
The motion of a guide star is monitored and corrections are made to an optical element in the light path to stabilize the image on
the main CCD. This technique can result in improved resolution and sharper images. In the case of a poor mount, it can mean the
difference between an unusable image and a good one. In the case of a good mount and good seeing it can mean the difference
between a good image and a great one. In comparison to the old AO-7, the new AO-8 can follow a guide star that is drifting over a
much wider range, about 40 arcseconds. Since most good mounts are capable of reducing periodic error to within this range, no
connection to the mount is even required to guide long exposures with arcsecond accuracy using the AO-8 and the ST-4000XCM (or any
ST camera). Moreover, the AO-8 is capable of making faster, better, moves than can be made by trying to correcting the mount.
This is a tremendous advantage, and a convenience. The images above, right, are both 15 minute exposures of the same double star
taken on the same night through the same scope, one right after the other, enlarged 300%. The image on the left is without the AO
and the image on the right is with the AO turned on. In this case the AO improved the brightness (peak value) and resolution
(FWHM) by approximately 30%.
5. Software Support
After all is said and done, if a camera is difficult to use at the telescope, no matter how good the hardware, image quality may
suffer. Getting focused, framing an object that is difficult to see, processing the results, etc., all go into the final result.
Good software makes these and other tasks easier to get right. The DSLR is designed to be used in one's hands without extensive
external control of the camera's functions when attached to a telescope at night. It can be done, usually by adding third party
software such as Maxim. This may add cost that needs to be considered. Like all other SBIG cameras, the ST-4000XCM includes more
excellent software than any other camera from any other manufacturer, plus some extras. Here is the software that you get with
the ST-4000XCM:
Free With Camera
CCDOPS version 5 is SBIG's full featured camera control software for Windows. Our own software package has evolved over the past
15+ years into one of the best, if not the best, basic camera control packages offered by any astronomical CCD camera
manufacturer. This software controls all camera functions, self-guiding, autoguiding, color filter wheel and adaptive optics. It
also has easy to use single-shot color processing for SBIG color cameras. CCDOPS is free with all SBIG cameras and can be
downloaded for free from our web site.
CCDSoftV5 Professional astronomical software package. Jointly developed by SBIG and Software Bisque, CCDSoftV5 incorporates
many of the camera control functions of CCDOPS, plus additional camera control features, in addition to its many other astrometry,
image processing and telescope control functions. CCDSoftV5 is included with SBIG CCD cameras at no additional charge. Purchased
separately it is $349.
TheSky Version 5 TheSky Version 5 is Software Bisque's well known planetarium and start charting software package that includes
telescope control for many popular telescope models. This is an indispensable tool for planning an evenings imaging session.
Field of view indicators for the imaging and tracking CCD, plus the ability to image link with CCDSoftV5 make TheSky one of the
most useful planetarium programs you can own. TheSky version 5, level II, (full functioning demo) is included with all SBIG
cameras at no additional charge. Upgrades from Software Bisque are available to higher levels and to the latest version 6.
EquinoX EquinoX software for Mac OS-X operating systems is a planetarium program that now includes SBIG camera control (check
with Microprojects for specific camera models). A free copy of EquinoX will be provided on request to new SBIG camea purchasers
running Mac OS-X systems.
Each new ST-4000XCM camera system includes everything you need to get started:
* 4.2 Megapixel KAI-4020CM Color CCD
* TC-237H Guiding CCD
* Built-in High Quality MAR Coated UV/IR filter for optimum color balance without external filter
* 4kps USB interface (up to 421,000 pixels per second)
* I2C bi-directional expansion port, compatible with the new CFW-10 filter wheel and AO-8.
* Standard accessory / telescope port
* User rechargeable desiccant plug.
* Dummy desiccant plug for dust prevention during recharging procedure
* Electronic shutter for fast exposure times down to 0.001 second
* Mechanical shutter for automatic dark frames
* 2" Nosepiece internally threaded for 48mm filters
* Cooling Fan - on/off controlled by software
* Latest heat exchanger design with water cooling capability
* Tripod mount 1/4-20 threaded side plate
* T-thread ring
* 15 foot USB cable (third party USB extenders available for up to 500 meters!)
* Adapter plug for telescope interface cable (for autoguiding)
* Telescope interface cable (for autoguiding)
* Universal 90-240VAC power supply with on/off switch and power on LED indicator
* SBIG's CCDOPS version 5 camera control software with new, updated, CCDOPS manual on CDROM
* Software Bisque's CCDSoftV5 camera control and image processing software
* Software Bisque's TheSky version 5, level II, with manual on CD-ROM, full working demo version.
* CCDStack, CCDAutopilot and other free trial software from CCDWARE
* Equinox planetarium and camera control for the Mac (on request with proof of purchase).
* Pelican carrying and storage case with custom cut foam
Optional Accessories:
* AO-8 Adaptive Optics
* Remote Guide Head
* 12VDC Power Supply
* 12VDC Water pump and tubing
* 110VAC Water pump and tubing
* 1.25" Nosepiece
* T-Thread Visual back for SCT
* CLA7 Camera Lens Adapter: Nikon or Canon FD
* Power Cable Extension
* Test lens
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