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Santa Barbara Instrument Group ST-5C, Руководство по эксплуатации

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Section 4 - Glossary

Page 23

4.

Glossary

Antiblooming Gate - When a CCD pixel has reached its full well capacity, electrons can

effectively spill over into an adjoining pixel. This is referred to as blooming. The

Antiblooming gate can be used to help stop or at least reduce blooming when the

brighter parts of the image saturate.

Astrometry - Astrometry is the study of stellar positions with respect to a given coordinate

system.

Autoguider - All SBIG CCD cameras have auto guiding or "Star Tracker" functions. This is

accomplished by using the telescope drive motors to force a guide star to stay precisely

centered on a single pixel of the CCD array. The camera has four relays to control the

drive corrector system of the telescope. The CCD camera head is installed at the guide

scope or off axis guider in place of a guiding eyepiece.

CCD - The CCD (Charged Coupled Device) is a flat, two dimensional array of very small light

detectors referred to as pixels. Each pixel acts like a bucket for electrons. The electrons

are created by photons (light) absorbed in the pixel. During an exposure, each pixel fills

up with electrons in proportion to the amount of light entering the pixel. After the

exposure is complete, the electron charge buildup in each pixel is measured. When a

pixel is displayed at the computer screen, its displayed brightness is proportional to the

number of electrons that had accumulated in the pixel during the exposure.

Dark Frame - The user will need to routinely create image files called Dark Frames. A Dark

Frame is an image taken completely in the dark. Dark Frames are subtracted from

normal exposures (light frames) to eliminate fixed pattern and dark current noise from

the image. Dark Frames must be of the same integration time and temperature as the

light frame being processed or numerous hot and cold pixels occur.

Dark Noise - Dark Noise or Dark Current is the result of thermally generated electrons building

up in the CCD pixels during an exposure. The number of electrons due to Dark Noise is

related to just two parameters; integration time and temperature of the CCD. The longer

the integration time, the greater the dark current buildup. Conversely, the lower the

operating temperature, the lower the dark current. This is why the CCD is cooled for

long integration times. Dark noise is a mostly repeatable noise source, therefore it can be

subtracted from the image by taking a "Dark Frame" exposure and subtracting it from

the light image. This can usually be done with very little loss of dynamic range.

Double Correlated Sampling - Double Correlated Sampling (DCS) is employed to lower the

digitization errors due to residual charge in the readout capacitors. This feature results

in lower readout noise.

FITS Image File Format - The FITS image file format (which stands for Flexible Image

Transport System) is a common format supported by professional astronomical image

processing programs such as IRAF and PC Vista. CCDOPS can save image files in this

format but can not read them.

Flat Field - A Flat Field is a image with a uniform distribution of light entering the telescope.

An image taken this way is called a flat field image and is used with CCDOPS to correct

images for vignetting.

Focal Reducer - A Focal Reducer reduces the effective focal length of an optical system. It

consists of a lens mounted in a cell and is usually placed in front of an eyepiece or

camera.  With the relatively small size of CCDs compared to film, focal reducers are

often used in CCD imaging.

Содержание ST-5C

Страница 1: ...Operating Manual for the Model ST 5C Advanced CCD Camera Santa Barbara Instrument Group...

Страница 2: ...rference 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...

Страница 3: ...ing Acquainted with CCDOPS Software 12 2 1 3 Connecting the Camera to the Computer 14 2 1 4 Establishing a Communications Link with the Camera 15 2 1 5 Operating your Camera with CCDOPS a Daytime Orie...

Страница 4: ...ii B Appendix B Maintenance 35 B 1 Replacing the Fuse 35 B 2 Disassembling Reassembling the Optical Head 35 B 3 Cleaning the Optical Windows 35 B 4 Replacing the Desiccant 36...

Страница 5: ...car battery 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 So...

Страница 6: ...ge 2 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 ab...

Страница 7: ...lectron 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...

Страница 8: ...e 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 u...

Страница 9: ...ge 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...

Страница 10: ...noise forms a noise floor below which the CCD will not detect weak signals Something you re imaging must rise above the read noise level before you ll be able to see it Since the read noise is the noi...

Страница 11: ...produce both protected and unprotected CCDs First off the process of Antiblooming protection causes a nonlinearity in the response of a CCD If you were trying to make accurate Photometric measurement...

Страница 12: ...form a single larger pixel This reduces the CCD s resolution but increases the sensitivity Different CCDs from various manufacturers support different types of binning Some CCDs support on chip binni...

Страница 13: ...Quantum Efficiency 1 4 Camera Hardware Architecture This section describes the ST 5C Advanced CCD Camera from a systems standpoint It describes the elements that comprise a CCD camera and the functio...

Страница 14: ...ing shutter wheel The shutter wheel makes taking dark frames a simple matter of pushing a button on the computer Remember that the shutter wheel does not perform the task of timing the exposure it mer...

Страница 15: ...the MS DOS prompt type CD then hit the Enter key to log into the root directory of your hard disk 3 Type MKDIR CCDOPS then hit the Enter key to create a directory for the software 4 Type CD CCDOPS the...

Страница 16: ...ahead now and move between these items The File menu is the most frequently used since it navigates you toward image retrieval Open command and the image Save command It also is the way to the off sw...

Страница 17: ...e Contrast Window control how the image is displayed Adjusting the Background setting and hitting the Do It Apply button changes the brightness of the image The Range setting controls the contrast You...

Страница 18: ...CCDOPS to you particular computer and graphics hardware For now let s move right over to the Track Menu Track Menu In the Track menu you see several commands Except for the Track and Accumulate comman...

Страница 19: ...ce the choices for temperature regulation etc Ignore these for the time being and hit the Cancel button or the Esc key to get rid of the dialog Again select the Camera menu and then execute the Grab c...

Страница 20: ...100 but that the pixels are much more closely clustered around 100 counts 3 If your room temperature is about 70 degrees F try further cooling to 8 degrees C Nearly 100 cooler capacity may be indicat...

Страница 21: ...surface behind the eyepiece tube and focus the telescope on the moon a bright planet star or a distant street lamp This preliminary step will save you much time in initially finding focus The approxi...

Страница 22: ...em on the screen one after another What you will typically see is a huge out of focus star image On an SCT if the focus is off enough you ll see an image of a donut with the telescope s central obstru...

Страница 23: ...difficulty finding an object after obtaining good focus you can remove the head and insert a medium or low power eyepiece Being careful not to adjust the focus knob on the telescope slide the eyepiec...

Страница 24: ...Section 2 The First Day with the Camera Page 20 below Advanced Imaging Techniques will also give you some good insight into how to effectively use your camera...

Страница 25: ...s available in CCDOPS which simplifies image acquisition for the typical amateur with a good telescope drive Drives employing PEC or PPEC technology and accurate gears only need adjustment every 30 to...

Страница 26: ...elescope drive corrector performance All the things that were important for good manually guided exposures still exist including a good polar alignment Use of an auto guider is to correct for the smal...

Страница 27: ...ed pattern and dark current noise from the image Dark Frames must be of the same integration time and temperature as the light frame being processed or numerous hot and cold pixels occur Dark Noise Da...

Страница 28: ...crons square 10 by 10 microns Planet Mode Planet Mode is the most useful way to achieve focus When you select Planet mode a full frame is exposed downloaded and displayed on the computer monitor A sma...

Страница 29: ...us Corporations to allow easy interchange of graphics images between programs in areas such as presentation and desktop publishing CCDOPS can save image files in this format but it can not read them T...

Страница 30: ......

Страница 31: ...Celsius below ambient Q Who should I contact when I have questions or problems with the camera Contact SBIG and ask for Technical Support If your questions are general in nature you might try subscrib...

Страница 32: ...ommand 3 Check for flexure between the CCD camera head and your system Check for flexure between the guide scope or off axis guider and your telescope system This is a very common source of guiding er...

Страница 33: ...nd power lines silhouetted against the sky work well as a target Use binning since turbulence will limit resolution This will allow you to learn the software flow in daylight Dark frames aren t necess...

Страница 34: ...components It is always possible to ascertain exact focus only after you have passed a peak intensity and then come back to the peak s setting You may not see the exact high value but will see the tre...

Страница 35: ...stars at the edge of the field can spray light across nebula especially Veil Horsehead California nebulae Anti blooming can t help scattered light Reposition field slightly and try again Due to small...

Страница 36: ......

Страница 37: ...rter 16 Bit 22 KHz Pixel Rate Power Requirements 12 VDC at 1 2 Amps Telescope Port 4 Open Drain Outputs Communications Port Interfaces to PC Parallel Port Electronic Shutter 01 to 3600 seconds Mechani...

Страница 38: ...No Connect Figure A 3 Telescope Port Note that the four outputs are active low open drain outputs without internal pull ups and are capable of sinking 250 mA DC to ground when activated They have a b...

Страница 39: ...d it necessary to take the two outer corners of the desiccant and turn them inwards making the rectangular packet somewhat conform to the round outline of the inner housing 2 Seat the O Ring in the gr...

Страница 40: ...emperature of the cooled CCD thus preventing the formation of frost The desiccant is contained in a small rectangular package inside the CCD chamber In normal operation the useful life of the desiccan...

Страница 41: ...1 Flat Field def 23 Focal Reducer def 23 focus Dim mode 19 Planet mode 24 Focusing 17 18 Frame Transfer CCDs 5 6 Frame Transfer CCDs def 24 frost 10 full well capacity 5 Full Well Capacity def 24 fuse...

Страница 42: ...ler def 25 telescope 19 telescope hand controller 19 22 telescope port 1 22 thermistor 4 TIFF format def 25 Tips 27 Track and Accumulate def 25 Track and Accumulate Command 21 Track List def 25 Tri Co...

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