Using the New Autoguider: A Tutorial

This page is a tutorial on using the new autoguider system.

You may also wish to read:

For information on using the tip-tilt system, see The UH-88-inch-Telescope Tip-Tilt system and Using the Tip-Tilt System.

Hardware setup
Using the autoguider
Working with the lens in place (KSPEC)
Focusing the Guider CCD
Fast Video Readout Mode
Optimization of Guiding
Problems
End of the Night shutdown

Hardware setup

Make sure all of the guider electronics are on.

Using the autoguider

Starting Up

Make sure tcsi is already running on tycho.

Log into viper as obs.

Launch a Terminal window for each application that you run. Diagnostic and error messages may be printed in these Terminal windows. You may iconify a Terminal window by hitting the little box in the upper left corner of the Terminal window.

Run Atlas.
You should always verify that the guide units are set to f/10 nominal or to f/31 nominal, depending on which secondary is mounted. The default value is normally the last value that was entered. If tycho has been rebooted, the default value will be reset.
Run MiniOtto.
When starting MiniOtto, say yes to all download, etc. options.

When you are asked which CCD configuration to use, you will normally be using the MiniOtto.cfg configuration file. If you are using the lens (KSPEC), select MiniOttoKspec.cfg instead).

Note: it is no longer necessary to set the guide-units-per-pixel.
Optional: Run AtlasMos
- check the TCS box and the (Mini)Otto box as well.
Focus the telescope on the science camera
Focus the autoguider CCD

Starting a new object

With tcsi (on tycho), use the x-y command to move the guide probe to the guide star.
In MiniOtto, Expose a full frame-the exposure time can be changed.
Once the star is on the CCD frame, move the cursor over it and click on it.
Press the Corner button to move the star to the corner.
Take another exposure to verify the star is now in the corner. If it isn't, just click on the star and press the Corner button again. If you are operating with the lens in place, you should always corner the star at least twice.
Press the Guide button.
Make sure the Enable Guide box is not checked.
Press the Start button. Verify that the signal is appearing in the four right most boxes of the 5x2 display. Check the signal level in the centroid display to make sure the signal is high enough above bias. Good signal levels are at least 5000 but no more than 15000.
If the signal levels are too high, you can reduce the integration time; if the signal levels are too low, you should raise the integration time. After adjusting the integration time or gain, press the Send button.

On a good night, the following values give reasonable results. This is only a starting point. You will need to adjust the values for best performance.

Guide-Star
Magnitude

Integration
Time (ms)

8

5

10

40

11

80

13

300
Press the Start button again to verify everything is working ok. If you have changed the integration time, you may want to check the values as in the previous step.
If everything is OK, Check the Guide Enable box.
Verify that everything is working. Make sure that you watch it for a while to see that it is guiding properly.
You are now guiding.

Moving around

To do short moves while guiding, use the guided offset T+P button in Atlas.

Stopping guiding

When you are done working on an object, stop guiding by pressing the Start button.

Working with the lens in place (KSPEC)

When the lens is in place, the system is more difficult to use. The user should be aware that the lens distorts and vignettes the field image which is on the guide CCD. Furthermore, with the lens in place, the XY-stage vignettes the field image on the guide CCD, when the CCD is too close to the limits of the XY-stage. The MiniOttoKspec.cfg configuration file is designed to reduce these problems, but at the cost of poorer performance.

Focusing the Guider CCD

The guider CCD sits on a stage with a total motion of 1 inch (25mm). It is controlled from the Atlas window. The stage can be moved IN or OUT. The distance it moves for each press of the buttons is set by the rate control. The total distance the stage can move is 60 units.

For normal f/10 and f/31 operation, begin with focus steps of 10 and search for the focus, and decrease the focus step down to 1 or 2 units for fine focus.

For f/31 with the 75mm lens, use focus steps of 3 and search, then use focus steps of 1 for fine focus.

Focusing can be accomplished using the Full Frame mode or by using the Fast Video Readout Mode, described below. If you use the Fast Video mode, remember that the seeing can have a time scale of several tenths of a second, so you should watch the image for a while after changing focus to make sure which way the focus has changed.

The stage takes a couple of seconds to respond after pressing the In or Out buttons, so be patient.

Warning! The focusing motor is not encoded. You will not know if you have reached a limit. The position of the lens is only approximate. E.g, moving one unit out, and then one unit in will not return you to your starting position.

Fast Video Readout Mode

The fast video mode is really a subset of the Guide mode, but without guiding enabled. It can do frame rates updated to the screen several times a second for a small subarray.

To set it up, you must be in Guide mode, by pressing the Guide button in MiniOtto. The subframe info for the guide mode must be changed. This is changed with the Configure window in MiniOtto. You will see a set of 6 text fields labeled in the lower half of this window. They work the same way as the standard CCD subframe window. You can choose the area of subarraying easily. Refer to the CCD manual for a better explanation of how to modify these parameters. For a 100 x 100 subarray in the corner of the chip (which reads out the fastest), use the following parameters:

-	X	Y
origin	50	0
size	100	100
bin	1	1

For focusing, a size of 50 is quite useful. For looking around (as in searching for a guide star) I would use:

-	X	Y
origin	50	0
size	256	256
bin	2	2

Warning! Do not press the set button after changing these parameters! Do not enter a carriage return while entering these parameters. Never press the SET button unless you understand what the set button does.

Warning! A more convenient and less error prone method is being developed to replace this procedure.

To return to normal operation, press the default button in the Guide subarray area, then press the Full Frame button or the Quad Cell button.

Optimization of Guiding

The binning size should be matched to the seeing conditions. The size of 10x10 is good for 1 arcsec seeing. If the seeing is significantly worse, the box should be expanded, perhaps to as much as 15x15. The pixel size is 27 microns or 0.2475 arcsec at f/10.

If the centroid is jumping back and forth a lot it is because:

the signal is too small or
something else is wrong

Problems

Problems and solutions:

You lose guiding but the program doesn't stop trying to guide.
This should never happen anymore; when guiding is lost, the display should turn yellow, and guiding should be temporarily suspended. If, for some reason, it continues to guide, it will probably run away very quickly. In this case, you should:
1. Disable the Enable Guiding box.
2. Press the INTR button in the MiniOtto Config window
The link does not respond after several tries
Sometimes, the link just dies. Reset the autoguider electronics by cycling the power on the black autoguider box.
The system seems to be working, guide signals seem to be getting sent, but the system is not correcting. Symptom: the same telescope-offset light is constantly flashing; the green balls on the guider display seem to be drifting away from the center.
There is an interface box that allows the guide computer to communicate with the telescope. Sometimes, this box gets into a state where it refuses to accept commands. You need to cycle power on the box. (Currently, it is located inside the TCS. It is a small box, labeled "TCS Guide Box")
The system seems to be moving randomly instead of guiding. Symptom: the telescope-offsets lights are constantly flashing, but there is no discernible pattern; the green balls in the guider display are appearing all over the display.
There is insufficient signal. Increase the exposure time. If this does not help, increase the averaging constant. If this does not help, increase the threshold value.
The system seems to be oscillating, instead of guiding. Symptom: Opposite telescope-offset lights are constantly being pressed; the ball on the guider display moves in a circular or elliptical pattern.
If the correction rate is too high, the guide signals can be sent at a rate that is faster than the natural frequency of the telescope. In this situation, the system will constantly be sending guide signals, and the guider will actually degrade the quality of the image. You can reduce the correction rate by increasing the averaging constant to make the system less sensitive to periodic fluctuations. You can also increase the threshold, to make the system less sensitive to errors.

End of the Night shutdown

This is very important.

Send a summary of any problems with the guider to the following people:

pickles@galileo.ifa.hawaii.edu
rjw@galileo.ifa.hawaii.edu
jim@luci.ifa.hawaii.edu
yamada@newton.ifa.hawaii.edu

If you don't say what is wrong, it will never be fixed.

This document was written by:

Using the New Autoguider

A Tutorial

Contents