SBIG ST-4 Operating Manual Download Page 34

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SBIG

ANTA

ARBARA

NSTRUMENT

ROUP

Page 32

SBIG ST-4/0490

X, Y

These are the X and Y coordinates of the

Crosshair. Location 1,1 is in the upper left

corner of the image.

Value

This is the intensity of the pixel directly under

the Crosshair as recorded by the ST-4, and is

a number from 0 to 255.

5X5 Ave

This is the average value of the pixel directly

under the Crosshair and all the pixels inside a

5 x 5 box centered under the Crosshair.

Stretched Data

Value

This is the intensity of the pixel directly under

the Crosshair as stretched by the

Background

and

Range

parameters to a value between 0

and 255.

5X5 Ave

This is the average stretched value of the

pixel directly under the Crosshair and all the

pixels inside a 5 x 5 box centered under the

Crosshair.

Magnitudes

Absolute

This the magnitude of the star underneath the

Crosshair. This value is calculated from the

pixel values within the 5 x 5 box, and

telescope and calibration data stored with the

image. In most cases an accurate calculation

of magnitude requires the sky background to

be subtracted. The Crosshairs should be

moved to a dark region of the image, and the

mouse clicked to take a background reading

(also, a square will be drawn on the image to

highlight the location of the background).

The

Absolute

parameter then displays a 99.

The Crosshair should then be moved to the

desired star; the background will be

automatically subtracted and the correct

magnitude displayed.

Diffuse

This is the diffuse magnitude, and is used to

measure the brightness of diffuse objects such

as nebulae or galaxies.

Geometry

Separation

and

Angle

These are the angular separation and the

angle (in degrees, clockwise of vertical)

between the current position of the Crosshair

and the background reference marker fixed

by clicking the mouse in the

Picture

window.

Note

The

Picture

window must be active before

clicking in it will place the background

reference box/marker used in the Magnitude

and Geometry calculations. This is why it

appears that you need to double click

sometimes to place the reference marker:

The first click is used to activate the window.

If you find that the calculated magnitudes or

separations are in error you can correct them by

adjusting the telescope parameters with the

Edit

info

command in the

Image

menu. Changing the

calibration factor or the telescope aperture will

change the calculated magnitudes. Changing the

telescope focal length will change the calculated

separation.

The Histogram

When an image is open, the

Show Histogram

command in the

Image

menu can be used to open

the

Histogram

window. The histogram is

normalized, with the greatest histogram point

representing a vertical value of 100. Also note

that the histogram data points corresponding to

pixel values of 0 and 255 are never allowed to

determine the scaling factor, so half frame

images, etc. will not have their histogram hidden

due to the large number of zero valued pixels.

On Macs with color or gray scale capability, a

color bar is shown under the histogram showing

the effects of stretching the image with the

Background

and

Range

contrast parameters. The

histogram window can be closed by clicking in its

close box or by invoking the

Hide Histogram

command in the Image menu.

Summary of Contents for ST-4

Page 1: ...cker Imaging Camera Operating Manual Table of Contents Instrument Overview Page 1 Star Tracking Operation Page 4 Imaging Camera Operation Page 8 Host Computer Software Overview Page 10 Using the ST 4 with an IBM PC or Compatible Page 18 Using the ST 4 with a Macintosh Page 28 Observing Suggestions with the ST 4 Imaging Camera Page 37 Problem Solving with the ST 4 Page 38 Appendix A Page 39 ...

Page 2: ......

Page 3: ... pixel position 121 132 the computer will determine its position by noting the increased signal from that pixel If the star is drifting due to guiding errors it will appear at a different position in the next exposure say at pixel position 123 132 The computer then calculates how far the star has drifted from the original exposure and toggles the telescope drive accordingly The microcontroller in ...

Page 4: ...umber of pixels much greater resolution would be degraded by the limitations of most computer graphics screens Note With the CCD running at lower than ambient temperatures you will wonder why dew and frosting aren t a problem First of all the chamber containing the CCD is small and only a small volume of air surrounds the CCD The small volume minimizes the total amount of water vapor in the air wh...

Page 5: ...r joystick type controllers the four relays in the ST 4 are used to simulate the joystick being pushed to its limits Two relays are used for each axis or rheostat of the joystick as shown in Figure 3 For the Right Ascension rheostat you would use the X and X relays and for the Declination rheostat you would use the Y and Y rheostat c no nc switch common normally open normally closed A Standard Han...

Page 6: ...CCD by completely blocking the open end of the telescope to remove all light the CCD is very sensitive it will saturate in very low ambient light levels 3 Observe the VALUE reading This reading should fall to a reading of around 10 and stabilize within two minutes of the instrument being powered on Press the INTERRUPT button to halt the FIND AND FOCUS mode or any other mode for that matter 4 Push ...

Page 7: ...e will also tend to smear the image so it may be helpful to watch several sequential exposures when critically focussing the image A table of typical VALUE readings for different magnitude stars is shown below in Table 1 This assumes a 1 second exposure and a typical response of the CCD Use this as a reference for determining whether the system is properly focussed Star ST 4 VALUE Reading Magnitud...

Page 8: ...ctions Care should be taken to orient the CCD head so the RA and Declination axes line up with the sides of the CCD head you can tell by looking through the glass window at the CCD or by noting the orientation of the Serial Number tag on the rear of the head which is oriented like the CCD This adjustment is not critical The tracker will work in any orientation It just makes it easier to make sense...

Page 9: ...is changed Many telescopes have severe backlash and the star image may not move for several seconds after a correction is made The parameter is the number of tenth second increments added to the calculated move when the move direction is reversed from the previous move H2 Hysteresis Adjustment Y axis This parameter is identical to the H1 parameter above except for the Y axis b Boost factor This pa...

Page 10: ...aken down to 0 01 seconds and the bottom half of the array shifted rapidly up to the upper half The 82 lines of short exposure data can then be readout at the normal rate This method works quite well and uses enough pixels such that 0 5 arcsecond per pixel scale factors can be achieved while viewing an entire planet Unfortunately this technique does not work for the moon since the moon s image typ...

Page 11: ... Film has the advantages of a much larger format color convenience and independence of the wall plug the ST 4 can be battery operated in conjunction with a laptop computer though After some use you will find that film is best for producing sensational color pictures and the CCD is best for planets small faint objects and general scientific work such as variable star monitoring and position determi...

Page 12: ...ensity less than 25 to be displayed as black any pixel values between 25 and 75 25 50 to be displayed with a gray scale and any pixels above 75 to be completely white You will want to experiment with the settings of the Background and Range parameters to get a good feel for how they affect the image These parameters do not physically change the image data but only affect the way the image is displ...

Page 13: ...s displayed on the computer screen pixel number 1 1 refers to the pixel with the x y location corresponding to the upper left hand corner of the screen X increases to the right and Y increases toward the bottom of the screen The position of pixel 1 1 on the CCD can be physically determined by referring to the placement of the serial number tag on the rear of the CCD head as shown below in Figure 4...

Page 14: ...e uses other image processing techniques besides contrast enhancement smoothing inversion and photometric analysis These other techniques are discussed in this section Flipping the Image Some inspection will reveal that the screen image is flipped about a horizontal axis relative to the CCD The horizontal and vertical flip commands enable a picture to be oriented correctly no matter what combinati...

Page 15: ...nicate at any baud rate from a lowly 1200 baud to the highest rate of 57 6K baud The actual baud rate used will depend on how you configure the host program and or the environment in which the host and ST 4 exist mainly the cable length between the host and the ST 4 The host software can be configured to talk to the ST 4 at the fixed baud rates of 1200 9600 19 2K and 57 6K or can be configured for...

Page 16: ...easing the signal level As previously mentioned you can not take infinitely long exposures because the CCD will eventually saturate from the effects of the dark current You can however add several long exposures after subtracting the dark frames from each of the light frames to make an image which while not exactly the same as a longer exposure will have the added benefits of greater signal to noi...

Page 17: ...T 4 subtract that dark frame from the light images immediately after the image is readout from the CCD and prior to it being sent to the host As always you must manually cover the telescope when you ask the host software to take the dark frame This is handy for searching an area for an object of interest but for your final images the ones you really want to keep you will want to capture and downlo...

Page 18: ...manually The telescope can be guided on a faint star by viewing the screen and making corrections which is much less fatiguing than guiding through an eyepiece in an awkward position This mode can be used to guide on stars too faint for the ST 4 to lock on since the eye brain combination is better at recognizing a faint stellar image in the presence of grainy readout noise In all the Focus sub mod...

Page 19: ...lescope can be quickly set close to the optimum focus the next time Replace the CCD head taking care to always seat it securely against the tube Now that you have found an object exit the Focus Mode and vary the Background and Range parameters to modify the display Small values of Range have the effect of increasing the contrast Stars get fatter due to the fact that the stray light near the main i...

Page 20: ...DOS manual and save the original in a safe place After successfully connecting the ST 4 to your computer power up the ST 4 and computer and run the program Note The PC version of the ST4 program CCD EXE requires several other files found on the floppy disk to run The CGA BGI EGA BGI etc files are graphics drivers for the various types of graphics cards supported by the program and the CCD CFG file...

Page 21: ...voking the commands to examine their associated command screens You can exit from a command screen and return to the menu bar by pressing the ESC key If you hit the ENTER key within any of the command screens that command will immediately execute Each command screen consists of several parameters which can be changed by moving to the desired line and changing the setting You move the flashing curs...

Page 22: ... the desired file using the cursor keys and hit ENTER again The file will be loaded the Status box will show an annotation attached to the image and the values of the telescope parameters associated with the image and the Data Buffer information box will be updated to reflect that fact that an image has been loaded After loading an image you would typically use the Display command to display it No...

Page 23: ...ntrast mode where the computer sets the Background and Range parameters based upon the image s histogram If you do want Auto Contrast don t change the setting of the Background and Range parameters below or the software will automatically deselect Auto Contrast before displaying the image This feature allows you to specify manual contrast mode by merely changing the setting of the Background or Ra...

Page 24: ...e of two things depending on whether the image had been previously zoomed or not shown in the upper left of the screen If the image had been previously zoomed and was not saved on the disk executing the Zoom command restores the image to its un zoomed state Otherwise executing this command enters Zoom Mode where a portion of the image can be enlarged to the full size of the image and is described ...

Page 25: ...entroid This command is like the Star command above but higher accuracy positioning of the reference is achieved for stellar objects by determining the center to subpixel accuracy Background This command records the background level used in the magnitude calculations to the average value of the pixels inside the box centered under the current position of the Crosshair Toggle box size Executing thi...

Page 26: ...cases you can set this item to to type of graphics adapter you have Strange and unusual results can occur if you specify a graphics card type that you don t have Note Some graphics adapters will support multiple modes such as VGA adapters that will also do CGA and EGA emulation These adapters can be used in any of their supported modes Also each supported graphics adapter requires a BGI file in th...

Page 27: ...b command Camera baseline level Set this item to the desired baseline level as described in the Baseline and Gain Parameters section before Gain expansion Set this item to the desired gain as described in the Baseline and Gain Parameters section before Telescope Setup Parameters Focal length Enter in this item the focal length in inches of the telescope you are using When images are downloaded fro...

Page 28: ...es enables the Auto Contrast feature when displaying the images downloaded from the ST 4 Background and Range These items are the Background and Range parameters used in displaying the images after downloading when the Auto Contrast feature is not enabled Frame size Set this item to the desired frame mode as discussed in detail in the Focussing and Special Imaging Modes section before Note The CCD...

Page 29: ...ame image needs to be changed at any point you should switch to Full Frame mode and then back to Quarter Frame mode starting the process over again Track Frame Initially this mode works like the Quarter Frame mode described above except that the rectangle is not quarter frame sized but 33 x 27 pixels in size After the rectangle is positioned hitting the ENTER key causes the Focus Mode to resume ta...

Page 30: ...ng the serial port you should use the Establish link command to establish a communications link with the camera If you didn t double click on one of the image files use the Open command in the File menu to open one of the image files such as the Dumbbell image file Elements of the User Interface This section describes the basic elements of the user interface for the SBIG ST4 application program We...

Page 31: ...image file gets opened the image is displayed in the Picture window and the Contrast window is opened You can only have one image file open at a time so you must close the current one if you want to open a different one Close Use this command to close an image file releasing it from memory If the image is new or has been changed due to some image processing functions you are asked if you want to s...

Page 32: ... appropriate settings for the Background and Range parameters the Auto Contrast feature and updates the image display with those settings Finally there are several check boxes in the Processing section of the Contrast window which are described below Expand 2X Selecting this item makes the image be expanded to twice its normal size Note Since the pixels on the Macintosh are square and the pixels f...

Page 33: ...ameters associated with the image discussed in the Telescope Factors section of the host software description above as well as some image cropping parameters Each item is discussed individually below Focal length This is usually the focal length of the telescope used to take the image but can be changed by zooming etc Aperture This is the aperture area of the telescope used to take the image Expos...

Page 34: ...tness of diffuse objects such as nebulae or galaxies Geometry Separation and Angle These are the angular separation and the angle in degrees clockwise of vertical between the current position of the Crosshair and the background reference marker fixed by clicking the mouse in the Picture window Note The Picture window must be active before clicking in it will place the background reference box mark...

Page 35: ...d selects a new color table which is an exact copy of the currently selected color table We suggest you use this command whenever you wish to modify an existing color table since any changes made to a color table can not be undone otherwise Also this button will be grayed out if the maximum number of 8 color tables already exists Ramp This button can be used to create a blend of colors between two...

Page 36: ... downloading images from the ST 4 you need to make sure the physical communications link between the Mac and the ST 4 have been established When the software is first run it will try to find the ST 4 If successful you can probably skip this section unless you desire to change the communications speed etc The Communications command in the Camera menu allows you to select which of the Mac s two seri...

Page 37: ...s you to select the desired frame mode as discussed in detail in the Focussing and Special Imaging modes section of the host software description above Some of the frame modes require further discussion below Quarter In this mode a full image is first downloaded and the Focus Mode is paused You then position a quarter frame sized square drawn in the Picture window and click the mouse to designate ...

Page 38: ...ight use the Grab Setup and Grab commands to take download and display a single exposure Use the Grab Setup command to set the Exposure time and Exposure delay items as desired Again the Exposure time can range from 0 01 to 600 seconds Setting the Exposure delay item to a non zero value causes the software to delay by that amount prior to taking the exposure giving you time to get back to the tele...

Page 39: ...tion of Jupiter can be easily seen in exposures only a half hour apart similar measurements can be made of Mars Use of color filters improves the contrast of planetary surface features Not as well known is that galaxies also change in appearance when color filters are used Old pictures of many galaxies were taken with blue sensitive emulsions and the dust lanes in the arms are very prominent At re...

Page 40: ...eature is helpful for example when no Declination motor is installed on the telescope mount PROBLEM Star images in photos are not round First check to see in what direction the images are smeared If it is in Right Ascension which is most likely consider the following possible problems 1 The guide telescope focal length is so short that adequate tracking is not possible The guide telescope should h...

Page 41: ...NTA BARBARA INSTRUMENT GROUP SBIG ST 4 0489 Page 39 using a guide star centered 1 degree away from the field of view of your camera this effect would cause each star to form a streak about 2 6 arcseconds long ...

Page 42: ......

Page 43: ...ack 2 Alarm relay1 common connection Orange 6 Alarm relay normally closed Blue 1 Alarm relay normally open White Table A2 Power Connector Cable ST 4 Wire PC Cables Mac Cables Pin Function Color PC XT 25 pin D AT 9 pin D 9 pin D 8 pin DIN 2 Transmit data from ST 4 Red 3 2 9 5 3 Receive data to ST 4 White 2 3 5 3 5 Ground Black 7 5 32 43 Table A3 RS232C Connector Cable For additional information reg...

Page 44: ...SBIG SANTA BARBARA INSTRUMENT GROUP Page 42 SBIG ST 4 0490 Telephone 805 969 1851 FAX 805 969 0299 ...

Page 45: ...mages 12 COM 1 or 2 16 Connecting to the camera 11 Contrast 8 Crosshair 9 10 D Dark current 2 7 12 Dark frame 1 4 12 13 Dark frame subtraction host 2 ST 4 13 Declination 2 5 Dew 2 Diffuse magnitude 10 Displaying images 8 Dithering 11 DOWN button 5 Downloading images 12 Dynamic range 13 E Error messages 35 Establish link command 12 Establishing communications link 11 Exposure 1 Exposure time 4 12 1...

Page 46: ... time 2 Interpolation 11 INTERRUPT button 3 Inversion 9 J L Joystick interface 3 Joystick type controllers 2 LEFT button 5 Light frame 1 12 M Macintosh 25 Macintosh software About dialog 25 Auto button 27 Camera Setup command 32 Color Table command 30 Communications command 31 contrast window 26 27 crosshair window 26 crosshairs 28 Customize command 33 Dithering menu 28 Do It button 27 Focus comma...

Page 47: ...GHT button 5 RS 232 1 16 RS 422 1 S Schmidt Cassegrain telescope SCT 2 Scribing the eyepiece 5 Separations 10 Serial interface 1 11 16 Serial port 11 16 Signal to noise ratio S N 12 Smoothing 9 Spot frame mode 14 Star tracking operation 3 overview 1 T TAKE DARK FRAME button 3 Telescope drive 1 Telescope factors 9 Thermoelectric cooler 2 7 TRACK button 5 Typical star intensities 15 Typical VALUE re...

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