Image capturing with N.I.N.A. and guiding with PHD2
After the telescope is aligned and focused, an exposure sequence can be started. This is described below using the programs N.I.N.A. and PHD2. (However, any other capturing software can be used. Here every astrophotographer has his own preferences).
The program N.I.N.A. is a free program, which has integrated all needed functions and automated processes and is a great support for the astrophotographer. It can be downloaded from https://nighttime-imaging.eu/download/. It is recommended to use the beta version, because in this version all functions are unlocked.
PHD2 is also a free and popular program for guiding and can be downloaded from https://openphdguiding.org/downloads/.
The basic settings required for the first capturing are shown below (N.I.N.A. version 2.0 HF1, PHD2 Version 2.6.11).
After the start the following view appears:
On the left is the menu bar (dark blue background) with the required functions. To the right are the submenu items belonging to the respective main menu item (highlighted in light blue). In the case shown, all submenu items of the equipment are listed (red long rectangle). The buttons in the green rectangle can be used to connect the equipment (individually - upper rectangle, or all at the same time - lower rectangle) to the software.
1) Start with the menu point 'Options' - 'General'
Here the general program settings as well as the observation location can be defined. If images are desired for display in the star atlas (green rectangle), they can be downloaded from https://nighttime-imaging.eu/download/. The storage location is entered in the upper right corner.
2) Entering the equipment specifications 'Options' - 'Equipment'
In this menu point, the used specifications for the camera and telescope are entered. For the focal length, note that reducers or Barlow lenses must be included. The program uses this value for plate solving.
3) Entering the capturing options 'Options' - 'Capturing'
Under this menu item, you can specify the components that should make up the image name. In this way, you can individually define which information is included in the image name, so that even months later you can still see which settings were used to create the image. The storage location of the capturing is also defined here.
For example, the suggestion in this image is:
However, it can be combined from the list below, for example to integrate filter names or image types such as dark-frames and flat-frames into the name.
On the right side specifications for the automatic meridian flip can be defined, but here the default settings are sufficient for the moment. (The side of the pier indicates on which side the telescope is currently located. Apparently there are mounts where this is incorrectly defined. For this rare case the slider can be set to 'ON').
A short explanation about the meridian flip: The meridian is an imaginary sky line running exactly vertically above the observation point from the north to the south pole (see menu item 'Components' - 'Mount and tripod'). The telescope follows the objects due to the Earth's rotation with the help of the motorized rotation of the right ascension axis during the imaging night from East to West.
If a tube would keep the position as in the left figure and continue to follow the object, it would hit a tripod leg after a short time after passing the meridian. To prevent this, the telescope changes the side when passing the imaginary meridian line. The image orientation is then rotated by 180°, but the stacking software automatically takes this into account and superimposes the images correctly.
4) Entering the capturing options 'Options' - 'Plate Solving'
In the tab 'Plate Solving' the settings for ASTAP (offline database) should be taken over. The installation for this can be found in the menu item 'Proceeding' - 'Alignment' - 'Alignment with N.I.N.A. using Plate Solving'. On the right, the parameters such as exposure time and Gain for the plate solving of the capturing sequence can be set. The Gain can also be set higher, the exposure time depends on the used filter.
5) Connect the camera under 'Equipment' - 'Camera'
After setting the options, the components are now coupled with the software. The first component in the submenu is the camera. If the ASCOM drivers have been installed (see menu item 'Proceeding' - 'Set up and wire'), the corresponding camera can be selected at the top of the screen and connected via the right button. On the right outside it is possible to start the cooling manually. At the bottom left, the values for Gain and Offset still have to be defined.
6) Connecting the mount under 'Equipment' - 'Telescope'
Under this menu point, only the mount has to be selected and connected.
7) Connecting the guiding software under 'Equipment' - 'Guiding'
The popular free software PHD2 is used for guiding. To use this in N.I.N.A., a few settings have to be made in PHD2.
Under 'Guide' - 'Connect Equipment' the guiding camera and the mount are set up and connected.
Also under the menu point 'Guide' the following settings can be recommended for 'Advanced Settings'. These vary for different conditions, setups and components and are not fixed values.
For successful communication between PHD2 and N.I.N.A. it is necessary to select the item 'Activate PHD server' under 'Tools'.
In order for the guiding camera to function properly, it needs dark-frames in order to filter out the dark current that may occur, or hot and dead pixels, so that these are not detected as stars. The recording series of dark-frames is started via the menu item 'Dark frames' - 'Dark frame library'.
Then, by clicking on the yellow star (at the bottom left of the main window), one or more guide stars are automatically selected.
If PHD2 has found guide stars successfully, the program must be calibrated. It learns the movement steps of the mount and can correct smaller gear and/or worm errors. To start the calibration, hold down the Shift key and click on the green target cross.
After calibration, the tracking starts automatically. To check if the selected algorithm values fit, the 'Tracking Wizard' can be started under 'Tools'.
After a successful run, the wizard issues recommendations.
A guiding resulting from such settings could then look like this:
In N.I.N.A., PHD2 can now be selected as software in the menu item 'Equipment' - 'Guider'. By clicking on the button with the setting wheel, the installation path of the guiding software is specified. This way, N.I.N.A. can independently start the guiding software and communicate with it when it is opened again.
With a click on the 'Connect' button N.I.N.A. connects to PHD2 and another settings window appears in the upper right part.
Parameters for dithering are defined here. With dithering, the image field is offset by a small amount after one or more captures. This ensures that stars no longer land on the same pixels. Hot or dead pixels that were not eliminated by dark-frames after all can be detected in this way, since these hot or dead pixels always remain on the same pixel, unlike the stars. The stacking software then detects these hot or dead pixels perfectly and can remove them.
However, this offset must be communicated to the guiding software, otherwise it would want to compensate this offset by command signals to the mount. If it knows the offset, it can offset the guide star by this value and then continue with guiding. The optimal offset can be determined with the calculation tool 'Dithering' in the menu point 'Tools'. Further explanations can also be found there.
Now all necessary components are connected and capturing can begin. N.I.N.A. offers a comfortable, but at the beginning a little difficult to understand procedure - the Advanced Sequencer.
8) Using the Advanced Sequencer via 'Sequencer' - 'Advanced Sequencer
The Advanced Sequencer can be used to define all the steps for a capturing sequence. It is possible to compile your own sequence, which can then be used again and again.
For this purpose, the required work steps on the right side can be dragged into the left free area and combined with each other. A possible sequence is suggested below, which can also be modified.
This process can be described as follows:
For a standard target, perform the following instructions:
- Slew to the target and center it
- Then start the guiding
- Now execute a sequential loop cycle that includes the following:
- Expose for 180s with specified binning and Gain
- Repeat this exposure until a defined time (here midnight)
- There are triggers that are allowed to interrupt this process:
- After 5 exposures, insert a dithering (image offset).
- After crossing the meridian perform a meridian flip
- Start guiding again after the flip
- If the time is reached in the sequential loop cycle, then stop guiding.
- Stop the camera cooling
- Move the telescope to the park position
This sequence can be saved and can then be found again under the templates.
Templates can also be stored there, which are helpful for the calibration frames.
A sequence for capturing bias-frames:
A sequence for capturing dark-frames:
A sequence for capturing flat-frames:
A sequence for capturing darkflat-frames:
For the creation of flat frames, it is helpful to view the current image of the flat frame beforehand under the menu item 'Capturing'.
At the top right, an exposure time can be set for the flat-frames. The command 'Rotate through' means that the images are taken without interruption. Now, by adjusting the time or by adjusting the brightness of the flatfield mask, the brightness in the image can be adjusted until the histogram in the statistics window is approximately in the middle. Once this is achieved, the sequence for the flat-frames can be started.
Alternatively, the 'Flat Wizard' can be used, which automatically determines the optimal exposure time.
In the window, the number of flat and darkflat frames is specified and then the 'Play button' is clicked.
9) Selection and planning of an object
The selection and planning of an object will be shown here as an example using M1 (Crab Nebula).
Objects can be selected under the menu item 'Star Atlas'.
The object can be searched directly at the top left, or parameters (such as max. height in the sky, only galaxies, etc.) can be entered for objects. All matching objects will then appear on the right. If the star atlas has been downloaded as described in point 1, black and white images are now also shown here.
The object can now be added directly to the sequence created in point 8 or displayed in an image alignment wizard. The camera position can still be adjusted in this. The image is automatically displayed in the 'Framing' menu item.
In order to get the correct image field width displayed, the correct camera parameters still have to be set.
If everything is set as desired, the object can be added to the previously defined sequence or saved as a target.
If the object was added to the default target, it can be found again under the 'Targets' tab at the sequencer.
Dragging with the mouse into the left area opens the sequence.
Pressing the Start button starts the acquisition series, and the first images of a deep sky object are created.