Almost all of the research facility telescopes are equiped with an auxiliary autoguider, a device which assists the main telescope in tracking a star for a longer time than the telescope alone is capable for. The 40-inch Fan Mt telescope is capable of tracking a star unaided for approximately 3-min (when pointing +-20deg off zenith).
Accurate tracking is essential for scientific imaging. For this purpose an ETF proposal was put forward to build an autoguider that would facilitate longer exposures.
The autoguider described in this manual, an interim step to the telescope's final autoguider, is capable of tracking up to 20 min. Most likely longer exposures are allowed but they have not been tested yet. It was put together during the summer of 2001 by Jim Barr, Jeff Crane, Charles Lam, Eugene Lauria, and Kiriaki Xilouris.
The autoguider consists of a digital camera (STV) connected to an 8-inch Meade telescope which is mounted on the main telescope tube, supported by a pivot stage. This structure enables limited but separate motion of the Meade with respect to the main telescope tube, increasing the possibility of finding a guiding star. Between the Mead and the STV camera there is a JIM focusing stage enable remote focusing of the Meade from the control room.
The autoguider can be controlled from its controller box which is mounted on the tailpiece of the telescope, or remotely from the comforts of the control room using the DELL III laptop and the RemoteAccess SBIG application. Similarly, the pivot and the focusing stage can be controlled from the control room and the Dome. Characteristics of the configuration
8" Meade LX Schmidt-Cassegrain Focal Length 2000mm Focal Ratio f/10 Resolving Power 0.56(arcsec) Image scale 0.72deg/inch STV pixel size 7.4 microns STV pixel 0.74 arcsec
When you leave for Fan Mt remember to take with you the DELL III laptop, usually kept in Kiriaki's office Room 210. You can control the autoguider without it, but it is much more comfortable to guide from the control room.
The autoguider should be already assembled and you should only have to hook the LapTop, DELL III. Check the Cable Connections in the troubleshooting section if the power-up procedure fails.
Make sure that
Starting the STV Remote
Click on the STV Remote icon (the one with the Helix nebula) .If all connections are established the PC Message window should say "Link established".
When you first power the CCD the alphanumeric display either on the contoller or on the Laptop will show a blinking diamond. At this point the STV is trying to automatically set an operating temperature according to the ambient temperature. The STV will attempt to run at the lowest temperature it can achieve using 70% power to the thermoelectric cooler. The diamond will stop blinking when the temperature has been set. (If during the night the CCD head warms up and the cooler power approaches 100%, you should reset the temperature to a higher number trying to keep the %figure to about 70-80%. If the night cools off, you can set the temperature to a lower number.
The general idea of how to command the controller is you press once, one of the buttons that designate functions such as Focus, Calibrartion and Track or SETup. This takes you to the menue of each function. To toggle through the Menue of each function use the Parameter button, or the rotary knob right underneath this button. If you are in the laptop REMOTE program you can press the TURBO button to accelerate the process. To actually change a value once you have chosen your menue, use the VALUE button and the knob undrneath it to adjust the value you want. Once you have set the values you want then press the FUNCTION button again to actually send the command and execute the function. If you choose to go in AUTO mode the from the beginning press the funtion button twice and let the STV take over for you.
Focusing Procedure
In Summary: Press the Focus button twice and adjust the exposure time with the selection buttons until you can make out light and dark areas in an image.
If you are in the Dome, the images appear on the control box of the STV, while in the control room and live video appears on the top video monitor. Do not be alert if the on-line video does not appear on the laptop. It is not meant to be. The laptop can show you only stored images taken with the STV.
Focus the 8-inch Meade by pushing the buttons in the focus handpadle constantly. Adjust the speed if you need to do so, from the rotary button in between the IN and OUT of focus button.
Once you are in focus move the Meade about its zero point position, and search for a bright star to help you do the focusing.
Toggle the zoom mode by pressing the Parameter button. Toggle the frame size by pressing the Value button. The best mode of operation when you do focusing is the Zoom, see below for explanation of what the various modes are.
The STV has 3 electronic zoom levels: Normal, Zoom and Wide. When the zoom level is set to Normal the central 640X400 pixels of the CCD are binned 2X2. This mode provides good balance of sensitivity and resolution. Good mode for galaxies. In the focus mode in order to increase the update rate by a factor of 2, only 60% of the entire image is shown.
For our configuration the relevant numbers are:
STV field of view 8X5arcmin (320X200 pixels) TV Normal mode 640X400 pixels binned 2x2 ==8x5arcmin STV Zoom mode 320X200 pixels 1x1 ==4x2.5arcmin STV Wide mode 656x480 3x3 ==8x6arcminWhen the zoom level is set to Zoom, the central 320X200 pixels are display unbinned (1X1). This mode has the lowest sensitivity but the best resolution and it is good for the moon and the planets. This is best for critical focusing and only 60% of the central part of the ccd is dislayed to increase the update rate by a factor of 2.
When the zoom level is set to Wide, the entire array of 656x480 pixels is binned 3X3. This gives the widest field of view and is the most sensitive mode. Best for imaging large dim objects.
Operation in Normal mode is always assumed. The longest exposure possible in Focus mode is 2.5seconds with the zoom level set to Normal. If you select zoom to Wide the max time is 2.2seconds and Zoom then it is 5.0seconds.
A more elaborate Focus mode is as follows. You will need to get into this mode if you need to adjust the sensitivity. You can adjust initial sensitivity by choosing Focus and then Parameter (sensitivity) and the Value (1 to 16) and then press the Focus button again. On the aphanumeric display you should see that you are indeed in Focus mode that the mode is NOrmal hat the exposure time is say 0.10s that the sensitivity is 1x and that the frame is Full. You can adjust any of these parameters. The gain is increased or decreased only when the exposure time is at 0.25seconds. When exposure time is 0.25sec and sensitivity times 4x, then the display also tells you the maximum pixel value (up to 1023) and the position of this pixel. That can also perceived as aa focusing indication.
The Focal length of the telescope is set in the SETUP menue and there is no need to play with it. However, in case the information is lost here it is and how to restore it. Press the SETUP button to enter the set up menue and either press the Parameter button to go through the various options or use the knob right below this button to do the same function. Once you reach the option Units press the VALUE button (or knob) to select between inches and cm for the Focal length and Aperture . Default setting is inches. The next Parameter is Focal length in our case this is 2000mm . To set the focal length use the Parameter button to go to the Focal length menu and turn the knob till you reach the desired value. The next Parameter is the Aperture Diameter which in our case is 203.2mmnd can be set as before.
Calibration Procedure
In Summary: Press the Calibrate button and use the AUTO mode to start with. The calibration is a prerequisite for autoguiding.This is the process where the STV learns how much and in what direction the telescope should be moved inorder to compensate for the telescope drift. A beginner is recommended to choose the AUTO mode, however here is more analytically what is happening.
The Caliration Setup contains the following options that you can select with the PARAMETER button (Mode=AUTO/Full-Menue, Move=moves in direction, View Resu lts). Under Full-Menu you can select (Exposure, Calibration Time, which RElay to mov e).
When you choose AUTO mode press the Calibrate button again and the STV will take an exposure, measure the brightness of the stars in the image, adjust the exposure time and finally mark up to 8 stars to follow throght the calibration process. The positions and relative brightness will be remembered and the calibration time will be automatically adjusted. If the stars are not found after a move then an error message will occur "STAR FIELD" indicatin g that the move was too much and the stars are out of the field. This calibratio n time is set by the parameter FOCAL LENGTH ath the SETUP Menue at the beginning . Very bright or saturated stars can be recognized as multiple stars incorectly and mess up the calibration. A succesful calibration ends up with a "Passed" on the alphanumberic display and four arrows showing relative orientation and speed of the four relays. To view the results of a succesful calibration s elect the VIEW results menue. This will display the results for each of the 4 Relays . It will display the speed in arcseconds per second and the direction in degree s.
If the AUTO mode does not work for some reason, here are some parameters you can adjust. First seletct the FULL-MENUE option and the adjust EXPOSURE time (from 0.001 to 600 seconds), Calibration time (0.1 to 60seconds), Relay (1,2,3or4). The calibration time is the amount of time the STV will close each relay to move the telescope for the purpose of calibrating the drive speeds. This time should be long enough to see a star moving 10-20 pixels but not longer to loose the star from the CCD field. Once yo have set these values, hit Calibrate again to start the procedure. The STV will take an image and report the number on the alphanumberic display the number of stars found and the initial position of the brighthest star. Then the STV will start moving the telsecope providing the following information on the same time. MV is the calibrate move time, RElay=1, Star=new location of the brightest star. If no motion is detected a "ERROR: NO Move" will be displayed and the procedure aborted. In this case use the MOVE menue to manually move the telescope to diagnose if there is somehting wrong in a connection.
Tracking Procedure
In Summary: After calibration is done press the TRACK button.
Like in calibration mode we have AUTO and Full-Menue. The TRACK set up menue has the folowing options (MODE=AUTO/FULL, Relay Tone =On/OFF). The Full-Menue has (Exposure=0.001-600s, Guide to=specify star by cursor, Agression X=aggressiveness of correction in X and Y respectively)
In the AUTO mode the STV will take an exposure, measure the brightness of the stars in the image, adjust the exposure time as necessary, select a guide star , set the aggressivenes to 1 and start autoguiding. Let the TOnE=On, good guiding you should hear short tones, bad guiding tone becomes longer and you might have to stop and go to MANUAL mode and adjust parameters and restart.
When you start to track the alphanumeric display will show the folowing inform ation. AEX=running average over the last 16moves in arcseconds in the X direction. AEY=running average over the last 16moves in arcseconds in the Y direction. X,Y =instantaneous error in arc sec , Brt=relative brightness of the guide sta r. If the brighness is reduced to less than 50% of the initial value, the STV will give a waring beep and display DIM on the top line of the alphanumeric me nue. The STV will continue guide as long as it can detect the star. If the star bec omes too bright and saturation occurrs a BRIGHT will be displayed. If the guide sta r is lost a "OFFCCD" will be displayed.
In the Full-Menue you can set the exposure from 0.001-600s. YOu can also select a guide star, press "Select Star" and move the box around the guide star you want.If you choose CURSOR the STV will move the current guide star to the cursor location that you position on the video screen before it starts guiding. Aggressiveness can be set between 0 and 2.0, default is 1 which means that the STV will make the exact move it calculates it needs to make to return the guide star back at its initial position. Aggressiveness of 0.5 means that the STV will make half of the move it thinks it needs to make for every correction and 2 means it will make twice the move. This feature is used to finetune the guiding accuracy. Selcting a number loer than 1 helps reduce oscillation or overcorrection. If you set this to 0, the STV will NOT make any correction in that axis. If you are tracking in the FULL-MENUE mode one more additional info is provided. Ifyou turn the knobs the AEX and AEY are now showing the aggressivene. You can adjust the aggressiveness and now see the effect on the tracking instantaneous error X,Y. After 16 corrections the average error will appear on the display again instead of the Aggressiveness.
Monitoring Procedure
By pressig the MONITOR button you get into the MONITOR SETUP
menue. Some useful options here are monitoring the seeing and
cheking the optical quality of the finder scope or graph
the drives periodic errors.
Pressing the Monitor button second time tells you which mode
you are in, you can use the Parameter to toggle through the
modes and the Value button to set parameters. If there is
a right arrow that also means there is menue there.
STV Normal mode 640X400 pixels binned 2x2 ==8x5arcmin
STV Zoom mode 320X200 pixels 1x1 ==4x2.5arcmin
STV Wide mode 656x480 3x3 ==8x6arcmin