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Internal Guider

Quick reference guide

The internal guider requires a system calibration once. Click on the calibration and select option 1 or option 2 (preferred).

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.

Option 2, calibration is fully automatic but requires a free sky view of in direction south (or north if you live at the southern hemisphere)

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”

If you have used calibration option 1 and the mount has executed a meridian flip and guiding is not working reverse the setting Reverse Dec output after meridian flip setting in tab option .

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

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. Once the 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. It is recommended to use option 2 of the calibration which will set all parameters correctly.

With option 2, the program will slew automatically to the SSW and calibrate the mount resulting in the values in tab advanced. Then is will slew in direction SSE and determine the correct setting for Reverse Dec output after meridian flip in tab options

Note for GS server users: If you use calibration option 2 the mount will temporary cross the meridian one hour prior to a flip. To avoid this set in GS the setting “meridian limit” from 20 to 0 degrees or use option 1 and check the guiding after the mount executes a meridian flip. If guiding is not working after a flip then reverse the setting Reverse Dec output after meridian flip in tab options.

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.

As soon the calibration is finished without errors you can start guiding.

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. See you camera manual.

Offset In most cases you can leave this at zero. See you camera manual.

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.
  • 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.
  • 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.
  • 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.
  • Reverse Dec after meridian flip This option should be checked for most setup. If after a meridian flip the camera is upside down then for most systems the declination output should reversed. So checkmark this option.

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.

Notes on guiding rate: The right ascension guiding speed is always forced at 0.5x the tracking rate. The declination guiding rate is not set and can be set by the user in the mount software. Leave the declination guiding rate at default which in most cases is also 0.5x. Guide rates below 0.5x would result in unreliable short pulses which are cut off anyhow by the shortest guide pulse setting.

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.

en/documentation/internal_guider.txt · Last modified: 2022/08/16 17:44 by han.k