Santa Barbara Instrument Group ST-237 User manual

PRICE $10.00
Operating Manual
for the ST-237
Advanced CCD Camera
Santa Barbara Instrument Group

Santa Barbara Instrument Group
1482 East Valley Road - Suite 33
PO Box 50437
Santa Barbara, CA 93150
PHN [phone]
FAX [phone]
Note: This equipment has been tested and found to comply with the limits for a Class B digital
device pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable
protection against harmful interference in a residential installation. This equipment generates,
uses, and can radiate radio frequency energy and if not installed and used in accordance with
the instructions, may cause harmful interference to radio communications. However, there is
no guarantee that interference will not occur in a particular installation. If this equipment does
cause harmful interference to radio or television reception, which can be determined by turning
the equipment off and on, the user is encouraged to try to correct the interference by one or
more of the following measures:
•Reorient or relocate the receiving antenna.
•Increase the separation between the receiver and the equipment.
•Connect the equipment into an outlet on a circuit different from that to which the
receiver is connected.
•Consult the dealer or an experienced radio/TV technician for help.
Changes or modifications not expressly approved by the party responsible for compliance
could void the user's authority to operate the equipment.
Also note that user must use shielded interface cables in order to maintain product within FCC
compliance.
ST-237 Manual
Second Printing
November 1999

i
Table of Contents
1. INTRODUCTION TO CCD CAMERAS....................................................................................................3
1.1. HOW CCDS WORK...............................................................................................................................3
1.2. CCDS APPLIED TO ASTRONOMICAL IMAGING ...................................................................................4
1.2.1. Cooling.............................................................................................................................................4
1.2.2. Dark Frames.....................................................................................................................................5
1.3. THE VARIOUS CCD PARAMETERS AND HOW THEY AFFECT IMAGING.............................................5
1.3.1. Pixel Size ..........................................................................................................................................5
1.3.2. Full Well Capacity............................................................................................................................ 6
1.3.3. Dark Current.....................................................................................................................................6
1.3.4. Read Noise........................................................................................................................................6
1.3.5. Frame Transfer .................................................................................................................................7
1.3.6. Antiblooming Protection ...................................................................................................................7
1.3.7. A/D Bits and Digitization Rate..........................................................................................................8
1.3.8. Binning .............................................................................................................................................9
1.3.9. Spectral Response............................................................................................................................. 9
1.4. CAMERA HARDWARE ARCHITECTURE ............................................................................................. 10
2. THE FIRST DAY WITH THE CAMERA ...............................................................................................13
2.1. SETTING UP THE SYSTEM.................................................................................................................. 13
2.1.1 Installing the CCDOPS Software..................................................................................................... 13
2.1.2. Getting Acquainted with CCDOPS Software.................................................................................... 13
2.1.3. Connecting the Camera to the Computer......................................................................................... 16
2.1.4. Establishing a Communications Link with the Camera.................................................................... 17
2.1.5. Operating your Camera with CCDOPS - a Daytime Orientation.................................................... 17
2.2. THE FIRST NIGHT WITH THE CAMERA.............................................................................................. 19
2.2.1. Focusing the Camera ...................................................................................................................... 20
2.2.2. Finding and Centering the Object ................................................................................................... 21
2.2.3. Taking an Image ............................................................................................................................. 21
3. SOFTWARE FLOW..................................................................................................................................23
3.1. IMAGE ACQUISITION ROUTINES........................................................................................................ 23
3.1.1 Grab ............................................................................................................................................... 23
3.1.2 Focus.............................................................................................................................................. 23
3.1.3 Track and Accumulate..................................................................................................................... 24
3.1.4 Eyepiece Mode................................................................................................................................ 24
3.1.5 Auto Grab....................................................................................................................................... 24
3.1.6 Color Grab...................................................................................................................................... 25
3.2. FILE OPERATIONS .............................................................................................................................. 25
3.2.1 Naming Conventions....................................................................................................................... 25
3.2.2 File Path and Filter......................................................................................................................... 26
3.2.3 Saving Images................................................................................................................................. 26
3.2.4 Loading Images............................................................................................................................... 27
3.3. IMAGE DISPLAY ROUTINES ............................................................................................................... 27
3.3.1 Photo vs. Analysis Mode ................................................................................................................. 27
3.3.2 Image Parameters........................................................................................................................... 27
3.3.3 Slide Shows..................................................................................................................................... 28
3.3.4 Printing Images............................................................................................................................... 28
3.3.5 Background and Range................................................................................................................... 28
3.4. IMAGE PROCESSING ROUTINES......................................................................................................... 28
3.4.1 Depixelize and Reduce.................................................................................................................... 29
3.4.2 Filtering.......................................................................................................................................... 29
3.4.3 Image Corrections........................................................................................................................... 30

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3.4.4 General Purpose ............................................................................................................................. 30
3.5. IMAGE ANALYSIS ROUTINES............................................................................................................. 30
3.5.1 Histogram....................................................................................................................................... 31
3.5.2 Cross Hairs..................................................................................................................................... 31
3.6. SETUP FUNCTIONS............................................................................................................................. 31
3.6.1 Camera Setup.................................................................................................................................. 31
3.6.2 Graphics Setup................................................................................................................................ 32
3.6.3 Communications Setup.................................................................................................................... 32
3.7. GENERAL PURPOSE CAMERA FUNCTIONS........................................................................................ 32
3.7.1 Establish Link ................................................................................................................................. 32
3.7.2 Information..................................................................................................................................... 32
3.7.3 Shutdown......................................................................................................................................... 32
3.7.4 Autoguiding.................................................................................................................................... 33
3.7.5 Filter Wheel.................................................................................................................................... 33
4. ADVANCED IMAGING TECHNIQUES.................................................................................................35
4.1. TAKING A GOOD FLAT FIELD ............................................................................................................ 35
4.2. TRACK AND ACCUMULATE............................................................................................................... 35
4.3. COLOR IMAGING................................................................................................................................ 35
4.4. AUTOGUIDING.................................................................................................................................... 36
4.5. FIELD OPERATION.............................................................................................................................. 37
5. GLOSSARY............................................................................................................................................... 39
6. HINTS AND TIPS......................................................................................................................................43
6.1 QUESTION AND ANSWER....................................................................................................................... 43
6.2. CCDOPS USE TIPS ............................................................................................................................. 45
6.3. HINTS AND TIPS FOR LAPTOP USERS................................................................................................ 45
6.4. TELESCOPE TIPS ................................................................................................................................ 46
A. APPENDIX A - SPECIFICATIONS ......................................................................................................... 49
A.1 DC POWER JACK................................................................................................................................ 49
A.1 COMMUNICATIONS PORT .................................................................................................................. 49
A.1 TELESCOPE PORT............................................................................................................................... 50
B. APPENDIX B - FILE FORMATS.............................................................................................................51
B.1 SBIG COMPRESSED AND UNCOMPRESSED FORMATS...................................................................... 51
B.2. TIFF FORMAT .................................................................................................................................... 56
B.3. FITS FORMAT .................................................................................................................................... 56
C. APPENDIX C - MAINTENANCE ............................................................................................................57
C.1. REPLACING THE FUSE........................................................................................................................ 57
C.2. DISASSEMBLING/REASSEMBLING THE OPTICAL HEAD.................................................................... 57
C.3. CLEANING THE OPTICAL WINDOWS.................................................................................................. 58
C.4. REPLACING THE DESICCANT............................................................................................................. 58
D. APPENDIX D - ADVANCED IMAGE PROCESSING TECHNIQUES ................................................. 59
D.1. ASTROMETRY AND PHOTOMETRY.................................................................................................... 59
D.1.1 Astrometric Measurements.......................................................................................................... 59
D.1.2 Photometric Measurements......................................................................................................... 60
D.1.3 Calculation of Centroids............................................................................................................. 62
D.1.4 Calculation of Separation ........................................................................................................... 63
D.1.5 Calculation of Magnitude ........................................................................................................... 63
D.1.6 Calculation of Diffuse Magnitude.................................................................................................... 64
D.2. FLAT FIELDING TRACK AND ACCUMULATE IMAGES....................................................................... 64

iii
D.3. FURTHER READING............................................................................................................................ 65

Introduction
Page 1
Congratulations and thank you for buying the SBIG ST-237 Advanced CCD Camera. This
camera offers incredible performance in a small package for a moderate cost. Using the camera
will expand your astronomical experience by allowing you to easily take images like the ones
you've seen in books and magazines, but never seen when peeking through the eyepiece. CCD
cameras offer convenience, high sensitivity (a typical deep-sky image is several minutes), and
advanced image processing techniques that film just can't match. While CCDs will probably
never replace film in its large format, CCDs offer ease of use and allow a wide range of
scientific measurements. Their use has established a whole new field of Astronomy. Some of
the features you'll discover about your camera include:
•Based on the Texas Instrument TC37 CCD with 640 x 480 pixels that are 7.4
microns square.
•Double Correlated Sampling readout with 12 Bit A/D for the lowest possible
noise.
•Convenient and fast parallel interface offers full frame download times under 4
seconds.
•Thermoelectric cooling and vibrationless fan give sky background limited
performance.
•Integral Shutter Wheel that can be replaced with a Color Filter Wheel for Tricolor
imaging.
•Telescope port for use as an Autoguider.
•Advanced CCDOPS software for data acquisition, display and processing.
•Track and Accumulate1for hassle-free long duration exposures.
•12 VDC wall transformer or use with battery in the field.
•Standard T-Thread allows use with a variety of telescope adapters including the
standard 1.25 inch nosepiece and eyepiece projection units.
This manual is organized for two types of use. Some sections have been designed to be read
through from the start while you're learning about the camera and the software whereas other
sections are to be used for reference. Briefly the manual consists of the following sections:
•Section 1 describes CCD cameras and how they work. While it is the first section
of the manual, it is a bit technical, and some users may wish to skip ahead to the
second section then come back to this section once they have had a little hand's
on experience.
•Section 2 tells you how to install the camera and camera software and takes you
step by step through the process of taking your first images. Even if you have
experience with other cameras you should browse through this section and read
any sections that are new to you.
•Section 3 describes the CCDOPS imaging software that comes with your camera.
It presents the software from the standpoint: "What commands do I use to take
1Track and Accumulate covered by SBIG US Patent 5,365,269.

Introduction
Page 2
images?", etc. While it doesn't discuss every nuance of each command (that's
reserved for Section 4) it will give you a good feel for the flow of the software.
•Section 4 presents some more detailed information about how you use the
camera for some slightly more advanced tasks. The discussion of even more
advanced topics is continued in Appendix D. Once you have become familiar
with the basic operations of the camera you will want to read these sections.
•A separate manual describes each and every command in the CCDOPS software
and is meant more as a reference section than a narrative one. If you're
wondering what the "Dark interval" setting in the Track and Accumulate
command does this section is for you.
•Sections 5 and 6 provide a Glossary of common CCD imaging terms, a Question
and Answer section on the most common questions you'll have and a section of
useful hints and tips for using the camera. Again, this is a good section to read
once you have had a little time with the camera.
•Finally, the Appendices provide a wealth of technical information about the
camera.

Section 1 - Introduction to CCD Cameras
Page 3
1. Introduction to CCD Cameras
The CCD (charge coupled device) is very good at the most difficult astronomical imaging
problem: imaging small, faint objects. For such scenes, long film exposures are typically
required. The CCD based system has several advantages over film: greater speed, quantitative
accuracy, ability to increase contrast and subtract sky background with a few keystrokes, the
ability to co-add multiple images without tedious dark room operations, wider spectral range,
and instant examination of the images at the telescope for quality. Film has the advantages of a
much larger format, one-step color, and independence of the wall plug (the ST-237 camera can
be battery operated in conjunction with a laptop computer, though). After some use, you will
find that film is best for producing sensational large area color pictures, and the CCD is best for
planets, small faint objects, and general scientific work such as variable star monitoring and
position determination. It is for this reason that we designed the camera to support both
efforts, as an imaging camera and as an auto-guider to aid astrophotography.
1.1. How CCDs Work
The CCD is a solid-state imaging detector that is quite commonly used in video tape cameras
and is starting to find acceptance in still frame cameras. It has been used for Astronomical
Imaging for over twenty years. The CCD is arranged as a rectangular array of imaging
elements called pixels. An image is formed by reading the intensity of these pixels.
The basic function of the CCD detector is to convert an incoming photon of light to an
electron which is stored in the detector array until it is read out, thus producing data which
your computer can display as an image. How this is accomplished is eloquently described in a
paper by James Janesick and Tom Elliott of the Jet Propulsion Laboratory:
"Imagine an array of buckets covering a field. After a rainstorm, the buckets are
sent by conveyor belts to a metering station where the amount of water in each
bucket is measured. Then a computer would take these data and display a
picture of how much rain fell on each part of the field. In a CCD the "raindrops"
are photons, the "buckets" the pixels, the "conveyor belts" the CCD shift registers
and the "metering system" an on-chip amplifier.
Technically speaking the CCD must perform four tasks in generating an image.
These functions are:
1) charge generation
2) charge collection
3) charge transfer
4) charge detection
The first operation relies on a physical process known as the photoelectric effect -
when photons or particles strike certain materials free electrons are liberated. In
the second step the photoelectrons are collected in the nearest discrete collecting
sites or pixels. The collection sites are defined by an array of electrodes, called
gates, formed on the CCD. The third operation, charge transfer, is accomplished
by manipulating the voltage on the gates in a systematic way so the signal
electrons move down the vertical registers from one pixel to the next in a
conveyor-belt like fashion. At the end of each column is a horizontal register of

Section 1 - Introduction to CCD Cameras
Page 4
pixels. This register collects a line at a time and then transports the charge
packets in a serial manner to an on-chip amplifier. The final operating step,
charge detection, is when individual charge packets are converted to an output
voltage. The voltage for each pixel can be amplified off-chip and digitally
encoded and stored in a computer to be reconstructed and displayed on a
television monitor."2
X=1 X=M
Y=1
Y=N
Output
Readout Register
Amplifier
Figure 1.1 - CCD Structure
1.2. CCDs Applied to Astronomical Imaging
When CCDs are applied to astronomy, with the relatively long exposure times (compared to
the 30 frames per second used in video camera), special considerations need to be applied to
the system design to achieve the best performance. This section discusses the cooling and dark
frame requirements of astronomical imaging.
1.2.1. Cooling
Random noise and dark current combine to place a lower limit on the ability of the CCD to
detect faint light sources. If the CCD is producing more electrons from its own internal
processes than is produced by photons from a distant object, the signal from the object is said to
be "lost in the noise", and will be impossible to display without sophisticated image processing
software. Noise here refers to the "gritty" look of short exposure images.
Internally, the CCD generates thermal noise and readout noise caused by the operation
of the electronics on the chip. The goal is to eliminate unwanted sources of electron production
in the chip and thus make the detector more sensitive to the remaining source of electron
production by incoming photons. As you can imagine, the reduction of unwanted noise is
important for the best performance of the CCD.
Dark current is thermally generated electrons in the device itself. All CCDs have dark
current which can cause each pixel to fill with electrons in only a few seconds at room
temperature even in the absence of light. By cooling the CCD, this source of noise is reduced,
2"History and Advancements of Large Area Array Scientific CCD Imagers", James Janesick, Tom
Elliott. Jet Propulsion Laboratory, California Institute of Technology, CCD Advanced Development
Group.

Section 1 - Introduction to CCD Cameras
Page 5
the sensitivity increased, and longer exposures are possible. In fact, for every 8°C of additional
cooling, the dark current in the CCD is reduced to half. In your camera for example, cooling
the CCD from room temperature (25°C) down to 0°C results in an eight-fold reduction in dark
current.
The ST-237 uses a thermoelectric (TE) cooler to cool the CCD. The TE cooler is a solid-
state device that acts like a heat pump. By running electrical current through the TE cooler,
heat is pumped out of the CCD through the TE cooler. The camera also has a temperature
sensing thermistor attached to the CCD to monitor the temperature, and the camera electronics
control the temperature at a user determined value for long periods. As a result, exposures up
to an hour long are possible, and saturation of the CCD by the sky background typically limits
the exposure time.
The sky background conditions also increase the noise in images, and in fact, as far as
the CCD is concerned, there is no difference between the noise caused by dark current and that
from sky background. If your sky conditions are causing photoelectrons to be generated at the
rate of 100 e-/pixel/sec for example, increasing the cooling beyond the point where the dark
current is roughly half that amount will not improve the quality of the image. This very reason
is why deep sky filters are so popular with astrophotography. They reduce the sky
background level, increasing the contrast of dim objects, and can be used to advantage with the
CCD camera.
1.2.2. Dark Frames
No matter how much care is taken to reduce all sources of unwanted noise, some will remain.
Fortunately, however, due to the nature of electronic imaging and the use of computers for
storing and manipulating data, this remaining noise can be drastically reduced by the
subtraction of a dark frame from the raw light image. A dark frame is simply an image taken
at the same temperature and for the same duration as the light frame with the source of light to
the CCD blocked so that you get an "image" of the dark. This dark frame will contain an image
of the noise caused by dark current (thermal noise) and other fixed pattern noise When the
dark frame is subtracted from the light frame, this pattern noise is removed from the resulting
image. The CCDOPS software can automatically perform this.
1.3. The Various CCD Parameters and How they Affect Imaging
If you scan the CCD related literature you will see a slew of new terms describing CCDs and
their performance. In this section we will discuss the more common CCD parameters and their
effects in an imaging application.
1.3.1. Pixel Size
Every CCD, independent of the manufacturer, is divided into a relatively large number of
small pixels. In your CCD camera the imaging area of the CCD is 4.7 mm x 3.6 mm and the
pixels are 7.4 microns square (1 micron is one thousandth of a millimeter or roughly 0.0004"). If
you looked at the CCDs available from the various manufacturers you would see that their
pixels typically vary from 7 microns on the small end to 25 microns on the large end. There are
advantages and disadvantages associated with the size of pixels in a CCD.