Note: This manual refers to the new or "Seitzer" autoguider.

TVGUIDER is a PC based guider running on both the 2.4-m and 1.3-m telescopes. It is a prototype for a system to completely replace the DTI boxes.

The system normally guides on the digitized video coming from the guider TV camera. Two cursors are implemented: one to mark the center of the finder field, and a second one to select guide stars. Full control is possible over the sampling of the video signal, and display contrast and brightness.

For acquiring faint objects, averaging of a 320x200 subfield is possible at 10 frames per second, or one can average a 120x120 subfield at full video rate (30 frames per second.) Pan around the main field while averaging using the cursor keys on the keypad.

IMPORTANT NOTE for the 2.4-m: the system works much better if you slow down the guide rates from the TCS default. Change the guide rates in the TCS to 1.0 for both ra and dec, and turn cos dec ON.

The old PC GUIDER system and DTI box are still available at the 2.4-m, but it does require changing the setup cabling. Let the staff know before your run if you wish to use it.

The new guider can be started or stopped using the xguider window on chichon. Parameters can only be changed from the PC keyboard.

• Getting Started
• Known Bugs
• Averaging
• Some Do's and Don'ts
• Guider Parameters
  • 1.3-m Parameters and Notes
  • 2.4-m Parameters and Notes
• Command Keys
• Remote Control of the Guider
• Differences with PCGUIDER
• Resetting the Frame Grabber

Getting Started

1. The PC should be running TVGUIDER after booting, if not, type:

           cd c:\tvguider
           tvguider
   

   the program will start up, restore all the last used parameters, and draw the cursors on the monitor.

   To be sure the program is initialized to all default values, type:

           tvguider -i
   

   The program will prompt you for which telescope you are on, and restore the appropriate values. Cursors are reset to the center of the screen.

2. select the guiding cursor (the square) by toggling with the 'c' key until the square cursor has 'hair' - 4 lines. It can now be moved with the numeric keypad number keys (with NUM LOCK off!) - diagonal motion is supported, and '5' shifts between step sizes of 1 or 10.

3. Turn up the high voltage, and after finding a quide star, hit 'z' for guiding on bright stars, or 'Z' for faint stars. This selects the optimum gain setting: the computer will then vary the offset as to set the sky level to between 30 and 60 units.

   (If the sky is very bright, this automatic set may fail. Then use the '1 2 3 4' keys to select a gain - I suggest 3 for most use, 4 for a very faint star (minimum dynamic range), and 1 or 2 for bright stars. Then repeatedly hit '5' to decrease or '6' to increase the sky value. Aim for sky between 20 and 60, as determined by the intensity reading on the lower right of the monitor, or returned when hitting the space bar on the PC keyboard. If all else fails, decrease the high voltage and try the above steps again.)

   The intensity displayed on the monitor is that corresponding to the central pixel of the active cursor.

   Saturation is 255 - but if a few pixels in the core of the star saturate, don't let it concern you. Guiding seems to be better if a few pixels are saturated (but not a lot - if the entire box is white, that is too much. Lower the gain.)

   With a 2 second average time, the system will guide on stars that are just visible in the raw video.

4. if needed, set the guider parameters with the 'p' key. If only the rotation needs to be changed, use the 'r' key.

5. All set? hit 's' to start guiding, and the x,y,dx,dy,sky total counts, and peak value will be printed out.

6. 'q' to stop. Guiding will also cease if the counts fall below a certain level (set with the 'p' key).

Known Bugs

If you have a bright star, and the guiding fails with 'not enough counts': increase the box size. Then check to see that the sky level is below 100 units. Use the 'b' or '5' keys to adjust if necessary.

If the telescope is moving without any command from the guider, try exiting the guider program and rebooting the PC (CTRL-ALT-DEL).

1.3-m only:

very rarely double images result. This appears to be a hardware problem in the guider mirror assembly. If this happens to you, please email to 'trouble' with as much information as you can provide: was the guide star still centered, where in the sky you were pointed, etc. One observer has reported this effect with the old DTI box and guider.

Averaging

This mode is essential for finding faint objects on the spectrograph slit. To use:

1. Hit the 'Z' key (capital Z) to set maximum gain and correct background. This mode works best at maximum gain for all sorts of reasons. If the sky is really bright, and the automatic background set fails, try gain 3 or maybe even gain 2.

2. hit 'a'.

3. select either the 320x200 subfield mode or 120x120 pixel subfield mode. The 120x120 mode will average at video rates (nothing is lost). The 320x200 will go at 1/3rd video rate.

4. select the number of frames to average. Note that in 120x120 mode 30 frames will take 1 second, but in 320x200 mode 30 frames will take 3 seconds.

5. the system will begin displaying averaged images on the computer's vga display. One can vary the brightness and contrast with the lowercase h-j-k-l keys: h and j adjust the black level down or up, k and l adjust the white level down or up. Try k followed by j. Each keystroke only changes the levels by a small amount: you may have to hold the key down for a while. If you get totally confused, hit the lowercase 'z' key to reset just the display lookup table back to the default.

6. one can pan the subfield around the full field using the keys on the numeric keypad. '5' resets one back to the full field center. Diagonal motion is supported. The position of the last subfield is remembered: on your next entry to averaging mode it will start up at the last location.

7. 'x' to exit and return to normal mode. The mode of averaging (320x200 or 120x120), the # of frames to average, the position of the subfield with respect to the full field, and the display brightness and contrast settings are all remembered.

Some Do's and Don'ts

     DO      use a guide box somewhat larger than the star.  Sky
             is determined from the outer 2 pixels of the box.
             Too small a box and if the star moves to the boundary
             the guider can't follow it.  Too large a box and
             the S/N is reduced.

     DO      keep the sky level between 30 and 100.  Too high a sky 
             level and the dynamic range is much reduced.  Too low
             a level and the pixel rejection schemes get confused.

     DO      adjust the high voltage before changing gain or offset.

     DON'T   expect great guiding if you change the box
             size or location when guiding.  Large errors
             can result due to buffer changes.

     DON'T   turn the DTI box on.

     DON'T   turn the PC off or disconect the cable from the
             PC parallel port while the telescope power is on.

     DON'T   disconnect the camera while running TVGUIDER
             in any mode.  The program uses vertical sync as
             its time base: if it loses it, guiding will
             cease and the program will tell you and will not
             allow you to resume until a video signal is restored.

     DON'T   get confused by the difference between gain/offset and
             display brightness/contrast.  Gain/offset control how
             the computer digitizes the incoming video signal
             with the 8 bit ADC.  The pixel value as displayed on 
             the TV is the digitized value, not display values.
             Display contrast and brightness can be changed using the
             h-j-k-l keys without changing the gain/offset setup.

             Thus white on the screen does not mean that a particular
             pixel is saturated (255 from the ADC).  You could have
             set the display contrast/brightness such that the display
             saturates (white) at a lower DN than the ADC.

             If you get totally confused, hit the 'z' or 'Z' keys
             to reset everything (including the display) back to
             default values.  Now display black = 0 DN, display
             white = 255 DN.

Guider Parameters

Hit the 'p' key to verify or change the guider parameters. If you are guiding, guiding will stop.

One can enter a new value, or just hit return to keep the old one.

The following are the parameters:

integration time (seconds):

how long do you want to integrate the TV signal before determining a guide correction? Less than 1 second probably isn't a good idea on the 1.3-m due to the slow response time of the relays. I've gotten good results with 2 seconds.

The algorithm followed is:

1. sum data within the guider box for the specified time.

2. determine the guide motion necessary.

3. apply it.

4. when the telescope stops moving, goto step 1 again.

ra guide rate

dec guide rate

These are the guide rates in terms of TV pixels per second of time the telescope moves. They are NOT arcseconds/second. To make a first guess, put a reasonably bright star in the center of the field, put the guider cursor on it, and hit the space bar. Note the position.

Then move the telescope a specified direction and time (10 seconds?) using the 'm' command. Measure the new position, and compute the rate.

This rate will be valid for large offsets, but probably overestimates the correction needed for small offsets.

fraction of guide motion to do

to cutdown on overguiding, one can tell the system to do only a specified fraction of the guide offset. The time the telescope will attempt to move is given by:

     time = fraction * (offset in TV pixels) / rate

with suitable adjustments for flip and rotation.

minimum guide time (seconds)

if the correction is less than this time, don't do it. 0.2 seconds on the 1.3-m? How long does it take the relays to respond?

This is a crucial value, because if you set it too large the system never guides. If set too small, the system is always moving.

Because the 2.4-m has much faster guide motions, a time of 0.05 seconds seems to be called for.

direct imaging (1) or off the slit (0)

are you looking at a slit or not?

rotater angle (degrees)

as read from the 2.4-m TCS or from the dial on the 1.3-m tailpiece (for angles > 0). This is the true position angle: there are no fudge factors.

This can also be set with the 'r' key if all other parameters remain unchanged.

minimum counts for guide star

if the total counts drop below this, just determine a centroid but don't try to guide. When counts exceed this start guiding again automatically. Experiments have indicated that this is somewhere in the value of 500 counts at maximum gain: below this level the guiding becomes uncertain.

automatically set sky level

Autoguiding works best if the sky is in the range of 30 - 60 counts out of a maximum of 255. If this option is set, then everytime one changes the gain or resets with the 'z' or 'Z' keys, the computer will take a series of frames and adjust the offset until the sky is in this range. For ease of use and quality of guiding, you really do want to leave this on. If there are very bright objects near the center of the field, the algorithm may get confused and manual adjustment may prove helpful (repeatedly hitting the 5 or 6 keys).

I strongly suggest that you leave this option enabled unless you know what the program is doing, or you run into serious problems. Much of the code depends on the sampling of the video signal being done right.

Disabling this option is provided only as a last resort.

1.3-m Parameters and Notes

The following values worked in April 1997 at a declination of +32 degrees and the new 135 mm guider camera:

        integration time        2 seconds
        ra guide rate           2 pixels/second
        dec guide rate          2 pixels/second
        fraction of move        0.5
        minimum guide time      0.2
        minimum counts          500
        direct imaging          1
        rotation                0.0

If you go back to the old 85 mm camera, new values will have to be determined.

The 1.3-m balance is critical - if the telescope seems to be bouncing in ra, have the staff check the balance.

NOTE: since there is no cos(declination) on this system, if you try to guide at high declinations one will have to change the ra guide rate to a lower value, else the system will never be able to correct enough in ra.

2.4-m Parameters and Notes

The following values worked well in November 2006 at a declination of +32 degrees and the 135 mm guider camera direct with the default TCS guide rates at 2.0: Default is cos dec ON.

        integration time        1 seconds
        ra guide rate           4.00 pixels/second
        dec guide rate          2.00 pixels/second
        fraction of move        0.5
        minimum guide time      0.05
        minimum counts          500
        direct imaging          1
        rotation                0.0

IMPORTANT NOTE for the 2.4-m: the system works much better if you slow down the guide rates from the TCS default. Change the guide rates in the TCS to 1.0 for both ra and dec, and turn cos dec ON.

Command Keys

The following keys are supported - other keys are ignored.

        # Guiding control
        s       start guiding                   
        q       quit guiding

        r       set rotater angle

        a       goto average mode

        # Cursor control - all guiding is done with square cursor
        c       toggle between cursors (active one has lines or 'hair')
        +       increase cursor size (maximum 41x41 pixels)
        -       decrease cursor size (minimum 9x9 pixels)

        # Cursor movement via keypad (NUM LOCK must be OFF!) - 
        #  diagonal motion can be done with the 1 3 7 9 keys
        5       toggle between steps of 1 and 10
        i       move selected cursor to center of field

        # video sampling
        z       set values for bright stars (min gain, max range)

        Z       set values for faint stars (max gain, min range)

        b       adjust sky to 30-60 units.

        1 2 3 4   select gain state 1 (low, max range) 
                        through 4 (high, min range)
        5       decrease background
        6       increase background

        space bar       quick sky and centroid of star in guider
                        box using data from last TV frame

        # display brightness and contrast
        h j     adjust black
        k l     adjust white

        f       transpose one frame and write to display.

        m       move telescope specified direction and time.    

        w       write full TV frame to disk as binary file of 8 bit
                integers: 512 columns by 486 rows.  Useful to see
                just how awful this data really is.

        p       set guider parameters (stops guiding)

        ?       type this help page             

        x       exit the TVGUIDER program.  *All* guider parameters
                and cursor positions and gain/offset values are
                saved to the file 'tvguider.ini' in the current directory.
                This file is read when the program is next started.

Remote Control of the Guider

TVGUIDER can respond to commands received over the serial line (9600 baud, 8 bits, no parity, 1 stop bit.) At the present time, only start guiding ('B'), stop guiding ('Q'), and resume ('R') are implemented.

These codes are an historical artifact of the old xguider program.

Any function of the guider could be controlled over the serial line with a few lines of new software. Contact the author if there is something you would like done.

Differences with PCGUIDER

TVGUIDER attempts to move the star to the center of the box, not to the first position. (I'll add this as an option.)

TVGUIDER computes a centroid first, and then guides, and does not attempt to determine new centroids while the telescope is moving.

Resetting the Frame Grabber

If the cursors vanish while not in averaging mode, or the board fails, or you suspect problems, exit the TVGUIDER program using 'x'.

Then type at the DOS prompt:

   cxdemo i

   cxdemo b
   cxdemo bi

If problems persist, check that the video cable is connected. Then exit TVGUIDER, turn the computer off for a minute, and restart.

Updated February 21, 2007 (rab/mdm)