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en:documentation:internal_guider

Internal Guider

Quick reference guide

The internal guider requires a system calibration once. Click on the calibration and select option 1 or option 2 depending on your mount and driver.

Option 1, first slew the telescope manually to a point in the sky at least 45 degrees away from the celestial pole, click on the Calibration button and wait till the calibration is finished.

Once calibration is finished click on the Guide button an check if guiding is satisfactory. Tune the Gain and Hysteresis settings if required. For the best star detection sensitivity make a master dark for dark subtraction in guider tab camera.

The trend scale can be adjusted with the up/down button in the graph. The trend unit is default in pixels. With the checkmark “in the XY-graph you can set the unit to arcseconds. Note that the conversion factor from pixels to arcseconds is measured during calibration. See documentation below.

Trending is suspended during dithering. Dither events are marked in the trend with a sinus ∿ character.

The XY-graph numerical values indicates the standard deviation of the right ascension (α) and declination (δ) trends. At a typical seeing conditions you can expect having guiding trends around one arcseconds standard deviation equals about 0.4 pixels standard deviation at a 2.5 ”/px scale.

A guide log CCDciel_GuideLog_YY-MM-DD_HHMMSS.txt in “PHD2” format is written to the log directory (Windows: %LocalAppData%\ccdciel\log) and can be analyzed in existing log viewers. To allow open and view CCDCiel guide logs you have then enter *.txt search pattern in the log viewer file&open menu.

Introduction

The internal guider is used to correct for small errors in a mount’s tracking like any guider software. This guider is build-in and doesn’t require an external program. The guider takes short exposures with the guide camera. From the star movements in the images if calculates the drift and send corrections to the mount to compensate. Note that it can not correct for the fast effects by seeing. So the right ascension and declination will always fluctuate typically about one arc seconds (or 0.4 pixels at 2.5 “/px) as indicated by the standard deviation values in the XY-graph.

Note: The tab internal guider will only be visible if you select the internal guider for guiding in preferences, auto-guiding and a guide camera in device setup, guide camera.

System calibration

Prior to use the internal guider requires a system calibration. During system calibration the guider will take an image, detect stars and then send guide pulses to the mount in direction East, West, North and South. Then it takes a second image and measures the movement of the same stars. By this it knows the effectiveness of the mount guide pulses and the orientation of the guider camera. This calibration takes a few minutes maximum. The calibration will be done in two phases. As soon the calibration phase one is finished without errors you can start guiding.

Note that as soon you slew to the other side of the meridian and start guiding a quick second calibration phase will be executed only to test the pulse direction. For more details se section tab advance.

Once the full calibration is done no more calibration is required unless you change something in your setup like binning setting, a new camera or telescope. The calibration is saved with the CCDCiel settings.

Set in tab camera the guider exposure time to a value between 3 and 5 seconds. Start a simple looping with the Loop button and check if the guider camera is in focus and some stars are visible. Stop the loop and go to the Guider tab and click on button Calibrate. After a few minutes maximum the calibration should be completed.

Backlash calibration: This measure the mount backlash when the declination movement change of direction.
The result is set in the Option tab where you can activate or not the automatic backlash compensation.

Tab Guider

Guiding is started with the Guide button in the first tab guider. Star detection is fully automatic. Even if guiding is interrupted by a cloud, the guiding software will recover automatically and continue with guiding unless an other action is programmed in a sequence.

For control there are two settings available for both right ascension and declination.

Gain. This sets the proportional corrective action in % on an offset. For right ascension typically set at 50%. For declination it is typically set at 50-70 %. If set too high the controller will overreact resulting in a oscillation. During oscillation the control action bars will show an East, West,East, West.. pattern or North, South, North, South… pattern. In this case reduce the gain.

Hysteresis. A percentage value. The controller will rely with the specified percentage on the last corrective action and reduce the new corrective action accordingly. Hysteresis is typically set at 30% for right ascension and 70% for declination.

Starting 09-2022: The declination controller has an output filter to prevent switching between North and South pulse corrections. There have to be at least three correction pulses in a different direction before they are passed unless there is a large correction pulse (>3 x min pulse duration).

In the XY-graph there is small checkmark to change the unit from pixels to arcseconds.

Tab Camera

In this tab you can set the exposure time and binning. For guiding use exposure times around 3 to 4 seconds. Note that guiding can only compensate for mount fluctuations and not for seeing effect.

Loop button. The loop button will start a loop taking continuous exposures and is intended for adjusting the focus of the guider camera.

Stop button. Stops the looping.

Dark button. This will start taking a dark for dark subtraction and store it. During guiding the dark will be automatically subtracted from the guide image improving star detection for noisy guide cameras.

Exposure Set the guide camera exposure time. Typical set between 3 and 4 seconds.

Binning Binning of the guide camera pixels. In most cases binning set at two works best.

Gain Camera gain. Set high enough for the short exposure used for guiding. See you camera manual.

Offset Use a value high enough to prevent low level truncation, this depend on the Gain.

Temperature If the guide camera has temperature control you can set the value here.

Gamma Stretch factor for your guide camera view. Set this slider in the middle. For more stretching move the slider to the right.

Luminosity For your guide camera view. Move the slider to the right for more brightness.

Tab Options

Options

  • Shortest guide pulse. This setting will block any guide pulse lower then the setting. At low duration values the guides pulse effect become so inaccurate that the resulting error can become larger then the intended correction. Blocking too short pulses will improve the stability. Default is 40 ms. Equivalent Minimum Move value is given below.
  • Longest guide pulse. The longest pulse correction used. This is also the value used to remove the backlash during calibration. You may have to reduce the default value of 2500 when using very long focal telescope.
  • Minimum HFD. Any star with a half flux diameter below this setting will be ignored. This setting can help to ignore hot pixels. If hot pixels are seen as stars and are annotated during guiding increase this value. To assist with setting this value the mean star HFD is reported in the log.
  • Minimum SNR. Any star with a signal-to-noise value below this setting is ignored. If your guide system detects sufficient stars you could increase the setting to filter out the faintest stars.
  • Frame size. Normally the full sensor area (=Max) of the guide camera is used for guiding. In case the guide camera has a very large sensor or the CPU load of the (small) computer used for guiding is too high you could set a smaller frame size. For example if you specify 100 then the software will download a 100×100 pixels frame only for guiding. As center of the 100×100 frame the brightest star location is used. Any other star found in this frame is also used for guiding. This smaller frame will reduce CPU load and download time significantly. For small frame sizes the guider will find and therefore use only one star (the brightest) for guiding.
  • Activate solar object tracking. This will allow the telescope to follow a solar object using the two parameters below. If checked the object will be sharp in the image but stars will form streaks.
    • Solar object apparent motion. The apparent motion of a solar object like a comet or minor planet.
    • Solar object apparent motion PA. The angle of the apparent solar movement CCW from north. Either filled by the connected planetarium or manual entered.
      The solar motion values can be imported from the connected planetarium program together with the object position. For this select “update position from planetarium program” in a sequence. Else the values have to be entered manually from MPC
  • Use backlash compensation activate the automatic backlash compensation. Use the backlash calibration to set the initial value. Note this is only a starting point value and the backlash is automatically adjusted based on the result during guiding.
  • Disable guiding. This will temporary stop all guide actions but the trend will continue. This can be useful to study the mount behavior without guiding.
  • Initial calibration step is the time in milliseconds of the first calibration move. Change only when using very long focal length with narrow guide image field.
  • Set guide speed, Set the guide speed you want for both RA and DEC. If unchecked it use the speed set in the mount driver.
  • Measure pixel scale [“/px] by stop tracking. The last field of the calibration result contains the conversion factor arcseconds/pixel. This value is used only for the trend to convert pixels to arcseconds and does not influence the guiding in anyway. It is measured by setting the pulse guide ratio of your mount software (e.g EQASCOM) to a pulse rate 0.5x and 1.5x times the normal guide rate. If the option Measure pixel scale [”/px] by stop tracking is check marked then the conversion factor will be measured differently during calibration. It will measure the conversion factor by stopping the mount tracking a few times for a 0.5 second and measure the total drift. It takes more time then the first method. Both methods should give about the same conversion factor in arcseconds/pixel. A third method would be to upload a guide image to nova.astrometry.net for solving and enter the found arcseconds/pixel manually.

Tab Advanced

Calibration results

Normally you should not change these calibration values. Just check if East and West values are about the same and the North and South values are the same. The field Pixel scale estimate [”/px] contains the measured conversion factor from pixels to arcseconds. See options.

Note: the following is valid for CCDCiel version compiled at 2023-09-4 or later:

There are three types of equatorial mount behavior. Typ “A” is typical for equatorial mounts controlled by Ascom. Type “I” for mounts controlled by Indi. Type “F for fork mounts and some equatorial mounts where the software adapt the pulse guide direction to the site of pier.

The calibration goes in two phases. Assume you have an equatorial mount with EqAscom mount control software and you calibrate your setup with the telescope pointing west. After the calibration you will see this:

  • Measured at[E/W]: W
  • Pulse North direction [cal/flipped]: N, ?

Guiding will work fine. Calibration of the other side of the meridian (east) is outstanding which is indicated by the “?

As soon you slew to the other side of the meridan (east) and start guiding a quick calibration phase will be executed and the following will be shown:

  • Measured at[E/W]: W:
  • Pulse North direction [cal/flipped]: N, S

If you start calibration at the east side of the meridian, you will get this result for EqAscom:

  • Measured at[E/W]: E
  • Pulse North direction [cal/flipped]: S, N

The last calibration date is reported and any issue. Note that the calibration does not age. Re-calibration is only required if your system setup changes.

These setting are overwritten after each calibration. The reported “pulse guide directions” are reported in the log during calibration. For some mount software like GS Server is is required to use the special calibration. This will simple set the option “pulse guiding is reversed after meridian flip”.

Guide image

The guider image is displayed similar as the images from the main camera. It is possible to zoom, save, swipe and solve the guide image.

Tab Spectroscopy

This tab activate special auto-guiding function for use with a reflective slit spectrograph.

Check Activate spectroscopy functions on top to enable the other options.

  • Activate single star guiding on fixed position When checked the program will guide on a single bright star, the one to measure, directly over the slit. To select the star use the right click menu Select guide star or double click at it's position. It is moved at the lock position when the guiding start, be sure the settle timeout in the auto-guiding options is large enough to allow this move.

    When unchecked it use multi-star guiding and you can set the offset to move the object to measure at the slit position. This is more suited to measure faint stars or nebula.
  • Guide position on the slit Indicate the X,Y position the object must be on the slit for the measurement. The button Click on image to set allow you to mark this position with the mouse. The position is marked on the image with a large green cross.
  • Use astrometry to identify the target, when guiding is started from a sequence or a Goto function, it take an exposure of the given time to solve and precisely identify the target position on the image.
  • Star search area When using single star guiding indicate the size of the guide box, this must include all the star light from both side of the slit. The maximum search box is used to find the brightest object to move at the lock position.
  • Multi-star guide offset When using multi-star guiding this allow you to move precisely the target at the slit position for measurement.
  • Draw slit area on the image this draw a red rectangle in the image where you can indicate the extension and rotation of the slit.
en/documentation/internal_guider.txt · Last modified: 2023/09/05 21:56 by han.k