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From the menu Edit → Preferences. Set the global preferences and options for the program.


You can change the program language from the list. The program must be restarted to change the language.

Capture folder
The base capture folder should be specified. The other configured sub-folder are created under this one.

Temporary folder
Normally you not need to change the temporary file folder. This is only required on Windows if the default path based on your user name contain accentuated non-ASCII characters. Be sure you specify a path with only ASCII characters.

File and folder name
You can specify how the image files are named and if they are stored in named folders. A typical imaging session will produce a great number of files, so this help to select files in the processing software.
One way of working is to make subfolders based on object name and select for file names all details; object name, the filter, a date sequence, exposure time, binning.
Select the separator character you want between the fields.
For folder name you have the choice between two date. One to make a folder with the same UT time as for the file name, the other is based on local time and change at noon to allow to put all the files for a given night to the same folder.
For file name, if Date/Sequence is checked the UT date and time is appended, otherwise a sequence number is appended. You can select a fixed sequence length or let unchecked for variable length.
You can reorder the different elements with a mouse drag and drop of the sequence number column.

At the bottom you can select to save all log messages to a file for further inspection or debugging. it is recommended to always let it checked.
You can look at the log using the function in the Help menu.
If this option is checked it also save the images in the case the auto-focus fail to find stars, they can be used later to help to adjust the parameters.
The log file and failed auto-focus images are conserved for a period of 30 days, then they are automatically removed.
In case of problem with a device driver you can get more detailed information by checking Verbose device log.

You can activate a TCP/IP server to get remotely the status of CCDciel.
By default the program show hint text over the buttons, you can disable this option here.


General information
The informations on top will be set in each FITS file for the OBSERVER, ORIGIN and TELESCOP keyword.

Observatory location
The latitude and longitude of the observatory is used to get the Alt/Az position of the object, or for the scope_alignment script. It is mandatory you set them before you can use the timing functions in the sequence planner.

Local horizon
The “Horizon profile” and “Minimum observing elevation” are used to compute the object rise and set time in the sequence planner. If this values are set the rise/set time are relative to this limits.
You can set only one value or both. In the last case the highest elevation is used.
The horizon profile file is the same as the local horizon line in Skychart.


The Dome preference let you configure if you want to automatically manage the dome with the mount park/unpark function.

If you check the box Allow to open the dome when safety status is bad or unknown there will be NO check for the safety before to open the dome. Use this setting only if your safety monitor is not functional until the dome is open.

If you check the box Automatically slave “Dome Park” to “Mount Park”, every time you unpark the mount from CCDciel the sequence to open and initialize the dome will be taken. And every time you request to park the mount the corresponding action to close and park the dome will be taken.

Beware to carefully test this procedure before use and be prepared if something go wrong. What to expect if for example the telescope do not respond to the park request but the roof is then closed and hit the telescope? This case can be secured by using hardware switch on the mount that prevent the roof motor to start.
If you are not sure please do not use this function and open/close your dome with manual action and visual inspection.

For each of the unpark and park function you need to select the action you want in the order require by your setup. For some configuration you need to open the dome first or unpark the telescope first.
If some action is not require by your setup just ignore it, you not need to fill all the rows. For example if unparking the dome also open the shutter select only “Unpark the Dome”.
But be sure to put “Unpark the telescope” and “Park the telescope” somewhere, otherwise the telescope will never be unparked and any slew will fail.

You can also wait for an additional delay between each operation to let time for the mechanical part to stabilize.


This settings affect only the preview, the FITS files are always recorded in RAW format to allow further preprocessing.

If you use a color camera you can debayer the preview image by checking the corresponding box and selecting the color pattern for your sensor. If you don't know what to select, make a test on a colorful subject on daytime. You can also do some color balance with the cursors on the right.

Reference image
The reference image help you to frame a previous image, for example to continue a sequence.
Select the threshold and color for the display of the reference image.

Image clipping
The image clipping indicator level. You can set the low and high threshold in ADU for this indicator.

Bad pixel map
The bad pixel map prevent the auto-focus function to lock on a hot pixel.
Select the threshold for detection of hot pixels for the bad pixel map.

Preview stacking allow you to stack the preview frames in real time. This feature is normally use for demonstration in public event.
You can select to disable this option to not risk an unwanted use during your imaging session.
Use the menu File → Dark frame to define the dark to be subtracted from the images before the addition to improve the result quality.

Select the preview rate for the video. Video require a suitable camera and is available only with INDI devices.


CCD temperature

Select if you want to use Celsius or Fahrenheit scale in the program. This also change the scale for the focuser temperature.

Configure how you prefer to cool down and warm up you CCD sensor.

Consult your camera documentation to know if you need to limit the temperature change.
In this case check “Limit temperature change” and indicate the maximum rate in degree per minute.

Check the corresponding box if you want your camera to start cooling as soon it is connect to the program and indicate the target temperature you want.

Sensor properties

Enter the camera pixel size and maximum ADU, or if applicable for your driver, check the box to get it automatically.
The maximum ADU is used to avoid saturated stars during autofocus and photometry.
The pixel size is required to speedup the astrometry solving by estimating the image scale.
You can select if you want to set the camera Gain from CCDciel or use the value you setup in the driver. If this box is checked the Capture and Sequence Gain selection are not available.

Readout modes

If your camera support different readout modes you can select which one to use for the different operations. Normally you want the select the best quality mode for Capture and a fast mode for the other.

You can select to Start new exposure as early as possible, without waiting for the previous image to be saved and displayed. With this option checked you can save a few seconds between each exposure, the gain is more important when using a big camera sensor with short exposure time.
This apply to capture sequence and preview loop.


Automatic flat
Configure the method to use to capture a flat series from a sequence.

Twilight flat
For the twilight flat it is require to configure the automatic exposure as the sky lightness change a lot during dusk or dawn.
You can also configure this automatic exposure for a use with other light source.
At each exposure the program will adjust the exposure time between the two limits to maintain the image level.\
Set the shortest exposure time that give an uniform sensor illumination. This depend on the kind of shutter used by the camera.
Set the longest exposure time you want for a flat. You have to take the corresponding dark separately.
Then give an image mean level range that make an acceptable flat. Start with 80% of your camera full range but check there is no saturated part in the center of the flat image, specifically if the vignetting is important.

Select this method if you use dome flat or light panel.
You can also select automatic exposure, but at the difference of the twilight flat the exposure is adjusted only once for each filter, then the same exposure time is use for the series.
If you need to point the telescope at a specific position to frame the panel you can enter the required azimuth and elevation.


Star profile
Select the size in unbinned pixel of the star detection area and the size of the zoomed window for the focus mode. If you use a binning different than 1×1 for the focus operation the window size is reduced accordingly.
Normally a single pixel star is rejected as a hot pixel. If your optical configuration produce undersampled image with single pixel star you can check this box. But be careful to make a bad pixel map to reject the hot pixel.

Focuser correction
If this is not already done by your focuser driver you can activate a backlash compensation. But be sure to let it disabled if the compensation is done elsewhere. Indicate the number of additional steps to use for the compensation, this must be greater than the actual backlash, don't hesitate to use a large value.
Indicate the direction the focuser will always finish to move, the best depend on your configuration. If you configure the auto-focus this control is disabled and will be set to the same as the focus move direction.
If it take some time for the focus position to stabilize after a move you can set a delay to wait after every focuser movement. This is more likely of use if the motor directly move the primary mirror of a SCT.

Focuser temperature compensation
If your focuser can measure the temperature you can set here the temperature coefficient (in steps per Celsius) used to adjust the focuser position between the exposures, or to shift the auto-focus V curve accordingly. The coefficient is positive if the focuser needs to move UP in position when the temperature drop. The routine will adapt the focuser if the temperature difference is larger then 0.5 degrees.
Note that for a reflector telescope you have to turn the focuser OUT to correct for tube shrinkage. For a refractor you have to turn the focuser IN since the change in refraction coefficient is dominant and much larger than the tube shrinkage.
The temperature coefficient will help to reduce the number of autofocus actions required. It will work best when the temperature drops slowly and all parts of the telescope have time to adapt to the changing ambient temperature.
The compensation factor has to be measured empirically. Start with an almost zero factor=1 and monitor the autofocus focus position in the log as function of the reported temperature. When you have enough data points which show a repeatable temperature coefficient enter the estimated factor in this menu. Some telescopes like a SCT could have less predictable coefficient and you most likely have to disable the coefficient and rely on the autofocus routine only.
If the factor is set well, the result of each autofocus routine run should be close to the previous focus position.
The temperature of the last focus operation in a session is saved to make a first correction the next time you start the program, so if no change was done in the mean time you recover a not too bad focuser position.
You can also request to run an auto-focus procedure if the temperature change is more than the configured value.

Filter offset
For each filter you can set an offset in focuser steps that will be applied to the focuser when you change the filter.
The filter exposure factor is used for the auto-focus functions and the automatic sky flat. For example if your R filter require 2x the exposure of the L filter and the Halpha 30x set : L=1 R=2 Ha=30
For narrow band filter this exposure factor can be very large. In this case you can use the option “Allow to select a brighter star for high filter exposure factor” in the auto-focus preference.


This section is initially empty. It can be hard to fill with the right values for your specific equipment. It is strongly suggested you use the focuser calibration wizard to set the correct default parameters.

After the wizard is run it select one of the focus method Vcurve or Dynamic depending on your focuser capabilities. You can return at this page if you want to change the method or adjust some parameters.

Select the auto-focus method:

  • V curve: (asymptote crossing) This is a method for an absolute position focuser. It will measure the size (HFD value) of a de-focused star at several focuser positions to calculate the best focus position. In advance your system has to be analyzed using the V-curve learning tool. This routine will measure the star size (HFD value) as function of the focuser position of your setup. The slope of the two linear lines (asymptote) left and right of the focus position are constant and they cross at the best focus position. Temperature changes, filters and slippage will only shift the focus but not the slope of the two lines.
    Once the V-curve (the slope of the two lines) has been measured accurately and saved using the V-curve learning tool, every auto focus operation will be done quick and efficient.
    This method work best with a single bright star and you need to configure the focus star magnitude you want to slew to before the autofocus routine is executed.
  • Dynamic: (hyperbole curve fitting) This method can be used with either an absolute or relative position focuser. Like the dynamic method it de-focus the star(s) and tries to fit the corresponding HFD values(s) to a hyperbole function. From the hyperbole function the bottom position so the focus can be calculated. This method has the advantage that it doesn't require a calibration in advance. It also requires less de-focusing of the stars (can work in bottom non-linear part of the curve) and therefore will work with fainter stars.
    This method will work well if you want to use the option “stay in place” for autofocus and it will use multiple stars for reliable detection.
  • Iterative: A dumb method that move in one direction or another as long the star diameter is smaller. It has the advantage to work with any kind of focuser and you can start with a very de-focused star. But it is slow and imprecise.
  • None: If you want to use your focuser only manually.

Performance comparison V-curve and dynamic focusing:

MethodTarget fieldV- curve focusingDynamic focusing
Slew to database starAlways a bright star +++ +++
Slew to database star +
Allow to select a brighter star
Narrow band filter +++ +++
Stay in placeMedium bright stars ++ +++
Stay in placeFaint stars + ++
Stay in placeNarrow band filter + faint stars - -
Dynamic focusing can work in the bottom non-linear part of the V-curve. HFD as low as 4 (twice minimum)
V-curve focusing requires a peak HFD value of typical 15 to 20. Below peak value HFD is 10, the focus result will be less accurate.

Common parameters

  • Exposure time to use for the auto-focus operation. This time is multiplied by the filter exposure factor above.
  • Binning to use for the auto-focus. Use binning 1×1 unless you are way oversampled.
  • The move direction of the focuser. Depending on you setting the focuser can work better when moved in or out of focus.
  • Autofocus tolerance is the maximum HFD that can be considered as a successful focus. If the HFD after and auto focus operation is higher than this value the focuser position is set back to it's previous value.
  • The minimum SNR of the star during the measurement. If a measurement SNR is higher than this value the auto focus operation is canceled and the focuser position is set back to it's previous value.
  • Number of exposure per point The number of exposure we take to get a mean HFD value for each focuser position. Increase this value if the seeing is not good. But set to 1 when using multiple stars detection.
  • Default behavior for Focus star selection. Select if you want to slew to a bright star or stay on the object you are imaging to do the auto-focus. This can be selected object by object in the target editor.
  • If you stay on position, you can select to Pause guiding during autofocus or not. You must pause when using a OAG, but you can continue guiding when using a separate guide scope.
  • Focus star selection when using “Slew to focus star”. Select the magnitude of a star that give a good SNR for the auto-focus operation using the above exposure time. The telescope is moved to a nearby star of this magnitude to run the auto-focus. You can set here the precision require for the slew to put the star in half the image height. Use a lower precision than for target slewing to speedup the process. If Allow to select a brighter star for high filter exposure factor the program can use a brighter star to avoid too long exposure time with narrow band filter.

If the auto-focus fails to find stars and the journaling to file is active, the image is saved in the same folder as the log so you can review them later to help to adjust the parameters.

V curve parameters

  • Start focus HFD: The focus starting point on the V curve used to determine the Near focus position. Use a high value near the top of the V curve but inside the measurement area. A typical value is 20.0.
  • Near focus HFD: We move the focuser to get this HFD to make the measurement on the V curve. This is not the focus HFD, it must be half way on the linear part of the curve. For example if your focus HFD is 3.0 and you make a V curve up to a HFD of 20.0, you can set 10.0 here.
  • Slippage correction If your focuser is prone to slippage you can activate a correction here. You must have configured the filter offset and the focuser temperature compensation, so we can be confident that the remaining offset is slippage.

The autofocus routine finds the focus in four focus movements using the slope information from the V-curve learning.

  1. Move beyond the Start focus HFD to (1) taken into account any temperature drift. This to fix any mechanical hysteresis in your system.
  2. Move to calculated Start focus HFD (2) taken into account any temperature drift. Here a number of exposures is taken and the average new start HFD is calculated.
  3. Based on the average new start HFD of step 2) move using the slope factor to the calculated Near focus HFD position (3). This (3) will be already adapted to any focus drift and should be spot-on. Take a number of exposures and use the average new near HFD and slope factor to calculate the new focus position.
  4. Move to the new calculated focus position (4).
  • - If the SNR, signal to noise is too low, the routine is aborted.
  • - Any focus drift will result in a drift of the new start HFD but not in the new near HFD.

Dynamic parameters

  • Number of dynamic points: The number of points we take on the curve. Do not set too high as this is done at every focus operation. Recommended default value is 7.
  • Movement between points: The number of focuser steps we move between each measurement of the curve. It must be set high enough to make a measurable change in star diameter, but not to high so faint stars can still be detected. The HFD value should increase at least twice the minimum. So if the focused stars have a typical HFD value of 2.5, the resulting V-curve should reach a HFD value of 5 or higher. Larger steps will make it less vulnerable for focus drift but due to the larger HFD values it requires brighter stars for enough signal to noise ratio. The maximum focuser movement in and out of current position will be (Number of dynamic points)*(Movement between points)/2

Iterative parameters

  • Initial movement in focuser steps. This is the movement we use between measurement on the first iteration. It is then divided by two every time we change the direction.
  • Final movement in focuser steps. When we reach this movement value we consider we are at the focus. This is typically the focus tolerance of your optical system.


Global options
It is important the program know your telescope focal length to estimate the image scale to speedup the solving process. Enter telescope focal length, or if applicable for your driver, check the box to get it automatically.

You can also adjust the timeout (in seconds) for a solve operation.

Software selection
Select the software you want to use for the astrometry resolution of the images, you can use , Star Locator Elbrus , PlateSolve 2 or ASTAP.

For each software you can adjust a few option to make them work quickly and reliably with your images. options

  • Maximum search radius: Is a tolerance in degrees to the telescope position. Set this value high enough if you use the plate solving to make a pointing model.
  • Scale tolerance: The tolerance on the pixel scale derived from the focal length and pixel size.
  • Downsample: the image by this factor. Use at least 4 or 8 for DSLR images. For CCD it is better to use binning.
  • Maximum number of source to consider.
  • Create plot of the result: create png image with indication useful for debugging.
  • Other options: any other option you want to give to the solve-field command.
  • Use custom script: Use a script instead of the solve-field command. There is two example with the program, one for remote execution using ssh, the other for remote solving with the python script.
  • On Linux or macOS you can specify the path to the solve-field program if it is not installed at a standard location. Let this field blank to use the default system search path.
  • On Windows only, you need to specify the Cygwin path to where is installed, for example C:\cygwin. See the installation instruction for more details.

Elbrus options

  • Elbrus images folder: the folder where Elbrus wait for new images to solve.
  • Images folder Unix path: Unix only, the unix path corresponding to the previous one where CCDciel save the image for measurement.

PlateSolve 2 options

  • Program folder: the folder you install the PlateSolve2 program.
  • Wait after solve: the number of second the PlateSolve2 window remain visible after solving is complete.

ASTAP options

  • Program folder: the folder you install the ASTAP program.
  • Maximum search radius: Is a tolerance in degrees to the telescope position.
  • Downsample: For large images (>3000 pixels wide) select binning.


You can adjust how to correct the mount position after plate solving a control picture.

Correction method

  • Mount sync will send a Sync command to the mount after plate solving before to Slew at the requested coordinates.
  • Pointing offset will compute the RA/Dec offset and send to the mount a Slew to coordinates modified by this offset.

If your mount allow to sync anywhere select “Mount sync”, if not select “Pointing offset” to make the correction in software.
“Pointing offset” can be useful if your telescope use a pointing model, this avoid any problem by using Sync with the model, but this can result in a wrong position to be reported in other software.
With Eqmod it is best to disable the pointing model and select “Mount sync” here. With EQAscom, in Alignment/Sync select “Dialog based” and “Nearest point”. With INDI EQmod select “sync mode=standard sync” and “alignment mode=nearest point”.

Pointing options
Then set the precision you want/can reach and the maximum number of pointing/correction retry before to give up. Beware that any backlash in the mount drive can limit the possible precision.

Set the parameters (exposure time, binning and filter) for the control exposure. This must give enough stars with your telescope/camera combination for the astrometry resolver to work.

If your mount need some time to stabilize after the movement you can increase the delay to wait before to take the plate solving picture.

Recenter sequence target that drift
For various reason you may observe the target to slowly drift in the image field during the night. The obvious symptom is large black border around the final image after registration and stacking.
You can observe this because you are not auto-guiding. But also when guiding with a separate guide scope because of slow flexion of different mechanical and optical parts.

With this option the program plate-solve every image taken during a sequence to compute the drift from the initial target position. If the drift is larger than the value set, it plan a recenter before the next exposure.
Because the plate-solving operation can be time consuming, you must also activate the camera option to start a new exposure as early as possible, without waiting for the astrometry result.
To make this possible it is required the image exposure time in the sequence is larger than the astrometry timeout.
The last point to check is the drift value you set here must be larger than 1.5x the slew precision and larger than 2x or 3x the dithering if any.


Configure here what you want to do when the mount reach the meridian.

  • Do nothing: select this option if your mount is not affected by the meridian (fork mount).
  • Automatic flip: automatically do a reversal of the mount to continue to track past meridian.
  • Abort: abort the current capture and stop the mount.

Automatic flip options

The first two parameters allow to loss the minimal time during a capture sequence. Set the difference between them as long as the capture exposure time. Otherwise the sequence can be paused until it reach the time for the flip.
Also be sure the flip do not start too early because this can be the cause of mount sync error in case of polar alignment error or telescope cone error because many mount do not accept to sync across the physical meridian.
To avoid error during the flip procedure it is important the mount and program observatory coordinates and time are set precisely.

  • Can track past meridian for: the number of minute your mount can safely track past the meridian without flip. This depend on the declination, set the smaller value here.
  • No flip until past meridian for: the minimum number of minute after the meridian we wait before to initiate the flip. Set this value to at least 10 minutes to avoid mount sync error near the meridian.

Actions to take as part of the meridian flip:

  • Autofocus after meridian flip: In some case the focus point can move after a flip.
  • Calibrate autoguider after meridian flip: If your mount do not report the side of pier to the autoguider you can check this option to force a new calibration.
  • Pause before meridian flip:
  • Pause after meridian flip: this two checkbox give you a prompt before or after the flip to let you the time to do some manual operation on the mount (moving the counterweight for example).
  • Timeout: The maximum time we wait for the pause after the meridian flip, if you not close the prompt after this time the sequence continue automatically.
    Before the flip the pause is limited by the maximum time the mount can track without a flip.

Precise centering of the target using plate solving after the flip is done automatically and only require you configure the plate solving correctly.


Software selection Select your autoguiding software, this can be PHD2, Lin_Guider or only dithering using mount command.

PHD2 options
For PHD2 you need to set the network name of the computer running PHD2 and the port number.

Set the options for dithering between the exposure, the number of pixel (in the guide camera) and if you want to dither only in RA (if you have a lot of DEC backlash).

Settle tolerance
The settle tolerance define how we consider the autoguiding as good after a dither operation or after it start.
It must stay within the number of pixel for Min.time. But we wait for the maximum of Timeout if this is not possible.
Set also the maximum time to wait if a new calibration is required.

Star lost action
In the case of guide star lost (passing clouds…) we can try to restart the guider after some time. This is useful if the star as moved out of the search area, but if the clouds are still there we can start guiding on a hot pixel. A value of zero disable this function.
Then we can abort the current sequence after some time, maybe the next object on the plan is in a clear area.

Lin_Guider options
For Lin_Guider you can choose to communicate by a local Unix socket or by the TCP network, on Windows only the TCP option is available. The selection must correspond to the one in the Lin_Guider general setting.

Set the number of pixels for dithering between the exposure.

Dither only options

With this option no auto-guiding is done but the program can initiate dithering between the exposure.

Here you set the mean duration of the dithering guide pulse send to the mount. This duration depend on the imaging scale and the mount guide rate. An additional wait time can be configured to let the mount stabilize after the dithering.


Select the planetarium application you want to use.

You can use the planetarium to select a target, or to display a solved image or image frame.

You have the choice between Skychart. HNSKY, or a SAMP application like Aladin or Topcat.

Weather station

Beware this settings will never close your observatory, even in case of rain! See the Safety monitor below if you need this actions.

You define here the parameters to pause a running sequence when the weather condition are not optimal.
When bad condition are detected the program do the following:

  1. wait the end of current exposure
  2. stop telescope tracking and autoguiding
  3. wait for the sky to be clear again

When it is clear again it run the target initialization procedure, the same as when the target is first selected, checking for time range, slew with plate solving, start autoguiding, eventually going to the next target if this one is no more observable.

When you select to use a ASCOM ObservingCondition driver, you need to set the limits for every sensors here.
For INDI the limits are the Warning level of the weather driver.

You can also set a delay to wait after the weather is good again to avoid to start/stop continuously if a sensor is just at the limit. See also if your driver can average the measurement over a period to avoid this behavior.

Safety monitor

Select the actions you want to run when the Safety monitor detect dangerous conditions.
Beware that by default it do nothing!

The order to run the different actions depend on your specific equipment and need to be carefully tested.
For example if it rain you want to close the dome as soon as possible, but maybe the mount need to be parked first. In this case you must also test what it do if the telescope cannot park because of cable disconnection or other reason.

Use the function “Call external command” if you need additional actions not available in the dropdown list.

For two actions you need to set a parameter:

  • Show prompt : the time to wait before to continue automatically, in seconds.
  • Call external command: the full path of the command or script to be executed.

If you configure the Dome operation to be slaved to the mount park/unpark you only need to use the “Park the telescope” action here to also park and close the dome as configured.

en/documentation/preferences.1573035886.txt.gz · Last modified: 2019/11/06 11:24 by pch