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en:ost:fokus_new [2020/09/10 19:27] – [Using MaximDL] rhainichen:ost:fokus_new [2026/03/10 13:29] (current) – rhainich
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-FIXME **This page is not fully translated, yet. Please help completing the translation.**\\ //(remove this paragraph once the translation is finished)// 
- 
 ====== Focusing ====== ====== Focusing ======
  
-A good focused telescope is essential for each successful observation, especially if deep-sky exposures shall be taken. With a small amount of exercise, an optimal focus can be easily found within a few minutes. The following small manual shall give assistant for this purpose.+A well-focused telescope is essential for every successful observation, especially when deep-sky exposures are taken. With a small amount of practice, the optimal focus can usually be found within a few minutes. The following guide provides assistance with this task.
  
  
 ===== General remarks ===== ===== General remarks =====
  
-The telescope is focused via an Electronical Focuser Assembly (EFA), which can be controlled manually or via the OMS. Since the EFA has a limited adjustment range (33mm), different adapters (M68) can be mounted on the EFA, so that the focus can be achieved with different instruments. +The telescope is focused using an Electronic Focuser Assembly (EFA), which can be controlled manually via a hand terminal or via the Observatory Management System (OMS). Since the EFA has a limited adjustment range (33mm), different adapters (M68) can be mounted on the EFA so that the focus can be achieved with different instruments.
  
 ++++ Calculation of the ideal adapter | ++++ Calculation of the ideal adapter |
-The back focus of the telescope is 147 mm (behind the EFA). The eyepiece clamp used has a back focus of 12.5 mm. The length of the ideal adapter ''D'' is therefore calculated as follows:+The back focus of the telescope is 147mm (behind the EFA). The Zeiss quick changer used has a back focus of 25mm. The length of the ideal adapter ''D'' is therefore calculated as follows:
  
-   D = 147 − 12,5 − 33/2 - C,+   D = 147 − 25 − 33/2 - C,
  
-where ''C'' is the backfocus of the respective instrument. The STF-8300 together with all attachments has a backfocus of 57.5 mm. Therefore, the ideal adapter for the STF-8300 is 60mm long.+where ''C'' is the back focus of the respective instrument. The STF-8300 together with all attachments has a back focus of 57.5mm. Therefore, the ideal adapter for the STF-8300 is 50mm long.
 ++++ ++++
  
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 /*|< 100% 33% 33% - >|*/ /*|< 100% 33% 33% - >|*/
 ^ Instrument               ^  Adapter [mm]  ^  Position of the EFA [μm]  ^ ^ Instrument               ^  Adapter [mm]  ^  Position of the EFA [μm]  ^
-| SFT-8300                 |  40+10  |  9500   | +| QHY600M                   |  20+10  |  16900  | 
-| Canon 700D               |  40+10  |  13000  | +| SFT-8300                  |  40+10  |  9500   | 
-| Baches + ST8             |  40+10  |  20200  | +| Canon 700D                |  20+10  |  13000  | 
-| Hyperionokular: 36mm     |  100    |  14500  | +| Baches + QHY268M          |  10     |  15000  | 
-| Hyperionokular: 22mm     |  100    |         | +| Baches + QHY268M + Barlow |  20     |  17500  | 
-| Hyperionokular: 13mm     |  100    |  25200  | +| DADOS + QHY268M           |   0     |  5000   | 
-| Canon + Superzoom        |  100    |  19550  |+| Hyperion eyepiece: 36mm   |  80     |  14500  | 
 +| Hyperion eyepiece: 22mm   |  80     |         | 
 +| Hyperion eyepiece: 13mm   |  80     |  25200  | 
 +| Canon + Superzoom         |  80     |  19550  |
  
-==== Manually ====+===== Focus using the hand terminal ===== 
 + 
 +A hand-held terminal (<imgref handterminal>) is available for manual operation of the EFA. The hand-held terminal is located in the movable storage container in the dome. The hand terminal must be connected to the black control box labeled //Electronic Focusing Accessory// on the back of the telescope. 
 + 
 +The cable of the hand-held terminal needs to be plugged into the port labeled //H/C// (see <imgref focusser_box>). The hand terminal itself should then be hung on a silver bolt in the immediate vicinity of the control box. **If the hand terminal is connected, control via the OMS is not possible.** Therefore, the hand terminal is usually not attached to the telescope. 
 + 
 +With the buttons ''In'' and ''Out'' on the hand terminal, the EFA can be moved inward and outward. The remaining buttons are intended for a derotator, which our telescope does not require. Therefore, these buttons have no function.
  
 <WRAP group> <WRAP group>
-<WRAP half column>+<WRAP third column>
 <imgcaption handterminal|Hand terminal for the EFA>{{ :ost:focusser:focusser_handcontroller_1.png?300 }}</imgcaption> <imgcaption handterminal|Hand terminal for the EFA>{{ :ost:focusser:focusser_handcontroller_1.png?300 }}</imgcaption>
 </WRAP> </WRAP>
-<WRAP half column> +<WRAP third column>
-\\ +
-\\ +
-\\ +
-\\ +
-\\ +
-\\+
 <imgcaption focusser_box|The control box of the EFA>{{ :ost:focusser:focusser_box_1.png?300 }}</imgcaption> <imgcaption focusser_box|The control box of the EFA>{{ :ost:focusser:focusser_box_1.png?300 }}</imgcaption>
 +</WRAP>
 +<WRAP third column>
 +<imgcaption handterminal_mounted|Back of the telescope with mounted hand terminal>{{ :ost:focusser:focusser_attached_1.png?300 }}</imgcaption>
 </WRAP> </WRAP>
 </WRAP> </WRAP>
  
-A hand-held terminal (<imgref handterminal>) is available for manual operation of the EFA. The hand-held terminal is located in the movable storage container in the dome. The hand terminal has to be mounted on the black control box labeled //Electronic Focusing Accessory// on the back of the telescope. The cable of the hand-held terminal needs to be plugged into the port labeled //H/C// (see <imgref focusser_box>), while the handheld terminal as such should be hung on a silver bolt in the direct vicinity of the control box. Please note that the handheld terminal is only relatively loosely attached to the bolt and therefore there is a risk that the hand terminal could fall off if the telescope is moved a lot. **If the hand terminal is mounted, control via the OMS is not possible**, therefore the hand terminal is usually not mounted to the telescope. 
  
-<imgcaption handterminal_mounted|Back of the telescope with mounted hand terminal>{{ :ost:focusser:focusser_attached_1.png?300 }}</imgcaption>+===== Focusing with the Observatory Management System (OMS) =====
  
-With the buttons ''In'' and ''Out'' of the hand terminal, the EFA can be moved in and out. The remaining buttons are for a derotator, which our telescope does not need. Therefore, these buttons are without function.  +Focusing via the OMS is performed using the program //PWI4//. In addition to controlling the focuser, this program also regulates the fans and the heaters installed in the telescope. These two aspects are described in more detail in the article [[en:ost:tempregula|temperature regulation]].
-==== Observatory Management System (OMS) ====+
  
-The focusing by means of the OMS is done by the program //PWI3//, which besides focusing also controls the fans and the heaters installed in the telescope. The last two points are described in more detail in the article [[en:ost:tempregula|temperature regulation]].+{{ :ost:software:pwi4_focus_2.png?800 |PWI4: Focus window including temperature display}}
  
  
-{{ ost:software:pwi3_focus_2.png |PWI3: Focus window}}+The operation of the EFA is largely self-explanatory. The current position can be found in the field ''Position'', while the EFA can be moved using the buttons ''IN'' and ''OUT''. The speed of the focuser can be adjusted under ''Jog'' by entering a value next to it. We recommend the standard setting of 200 micron/s.
  
-The operation of the EFA is basically self-explanatory. The current position can be found in the field ''Focus Status'', while the EFA can be moved via the buttons ''IN'' and ''OUT''. From a drop-down menu, one can select ''Fast'', ''Slow'' and ''Increment'' for the speed. Using the ''GOTO'' menu, the EFA can be moved to a specific position.  An ongoing movement can be stopped at any time using the '' STOP '' button. The temporal course of the temperature of the main mirror, the support of the main mirror, the secondary mirror and the ambient temperature can be shown and hidden using the buttons ''SHOW'' and ''HIDE'', respectively. +Using the ''GOTO'' menu, the EFA can be moved to a specific position. An ongoing movement can be stopped at any time using the ''STOP'' button. The temporal evolution of the temperature of the main mirror, the support of the main mirror, the secondary mirror, and the ambient temperature can be shown or hidden using the buttons ''SHOW'' and ''HIDE'', respectively.
  
-{{ ost:software:pwi3_focus_3.png |PWI3: Focus window including temperature display}}+==== Auto Focus ====
  
-=== Auto Focus ===+Manual focusing can be tedious, even when a suitable focus point is already known from previous observations. For this reason, several programs offer automatic focusing methods. Here we list focusing with //PWI4//, //MaximDL//, //NINA//, and others. The program used depends on the observer's preferences and the target.
  
-//PWI3// also offers the possibility of automatic focusing. For this purpose, //PWI3// connects to [[en:ost:ccds:maximdl|MaximDL]] to take the necessary pictures. Hence, before starting the automatic focusing, the camera must be connected to //MaximDL//. With a click on ''AF CONFIG'' the settings can be adjusted. One of the most important settings is the ''Step Size (micron)'', which defines the step size in micrometers that the EFA should move at each focusing step. ''Steps (Image Count)'' is the number of focusing steps performed by the EFA and the number of images to be captured. The exposure time in seconds must be specified at ''Exposure length (sec)''. So far the following settings have proven to be useful:+=== Maxim DL ===
  
-    Step Size (micron)    = 500 +<WRAP center round todo 60%> 
-    Steps (Image Count)   = 5 +This part needs to be written. 
-    Exposure length (sec) = must be chosen depending on the object+</WRAP>
  
-**ToDo: More to come!**+=== NINA === 
 +{{:ost:software:nina_autofocus_start.png?nolink&300 | NINA Autofocus}}
  
-===== Using MaximDL =====+In //NINA// the autofocus can be started by selecting ''Imaging'' and then selecting autofocus on the right-hand side. After selecting autofocus, //NINA// will automatically start the process.
  
-All our SBIG-CCD cameras can be controlled via //CCDOPS// as well as //MaximDL//. Here we will first concentrate on //MaximDL// before we deal with //CCDOPS// below. The most important functions of //MaximDL// have already been introduced in the main article on [[en:ost:ccds:maximdl|MaximDL]].+Note that the focuser must first be started via //PWI4// and connected via the **Equipment** tab. Furthermore, //NINA// will use whichever filter is currently selected.
  
-The best way to focus is to use the //Exposure Preset// ''Focus'', which can be selected via the corresponding drop-down menu in the //Exposure Tab// of the //Camera Control// window (see below). In this preset many settings, important for focusing, are already pre-selected. In the examples shown below the exposure time (''Seconds'') is set to one second, this must be adjusted according to the object used for focusing.+A successful autofocus run can be recognized on the left side of the interface, where a clear hyperbolic relation becomes visible. In the example shown, the run took about 6:30 minutes and determined 6612 as the optimal focus position for the clear filter.
  
-{{ ost:software:maximdl:focus_maximdl_1.png |}}+Under ''Options > Autofocus'' the settings for fine-tuning the autofocus can be found. An image of these settings is shown below the documentation.
  
-After a click on ''Start'' images are continuously taken and displayed. Now the telescope can be focused by means of //CW3// or the hand terminal of the EFA. To find the coarse focus, it is recommended to first approach a bright star and to focus in such a way that the diffraction ring disappears. Rough values for the focus with the different instruments and eyepieces can be found in the table above.+  * **Use filter offsets** lets you apply predefined offsets per filter instead of refocusing every time (currently not available; test observations required). Default: OFF 
 +  * **Autofocus initial offset steps** determines how far the focuser initially moves outward to start the autofocus. Default: 10 
 +  * **Autofocus method**: Default: Star HFR (Half-Flux Radius of stars) 
 +  * **Curve fitting strategy**: Function used to fit the measured data points. Default: Hyperbolic 
 +  * **Number of attempts**: How many times //NINA// retries autofocus if the first attempt fails. Default: 1 
 +  * **Use brightest n stars**: If >0, only the n brightest stars are used instead of all detected stars. Default: 0 
 +  * **Outer crop ratio**: If 1, the overscan region is cropped. Default: 1 
 +  * **Binning**: Pixel binning during autofocus. Default: 2×2 
 +  * **R² threshold**: Minimum quality fit for the autofocus curve before retrying. Default: 0.8 
 +  * **Autofocus step size** determines how far the focuser moves between samples. Default: 150 
 +  * **Default autofocus exposure time**: Exposure duration (in seconds) per autofocus frame. Needs to be adapted for other filters. Default: 6 s 
 +  * **Disable guiding during AF**: Turns off guiding while autofocus runs. Default: off 
 +  * **Focuser settle time**: Delay after a focuser movement to allow mechanical settling. Default: 1 s 
 +  * **Number of exposures per point**: How many frames are taken at each step. Default: 1 
 +  * **Inner crop ratio**: Fraction of the frame used for detecting stars. Default: 0.5 
 +  * **Backlash compensation method**: Method used to cancel mechanical backlash. Available are ''Overshoot'' and ''Disable''. Default: Overshoot 
 +  * **Backlash IN/OUT**: Step count used to clear backlash when moving in or out. Default: 20,0
  
-In order to further optimize the focus, a globular cluster can be observed. The low angular distance between the stars in a globular cluster facilitates very good focusing results, since the Airy discs of the individual stars can only be separated with a very well focused telescope. An optimally focused telescope operates with a seeing limited resolution, which for our site is often larger than 2“. This is significantly worse than the diffraction limited resolution of our telescope, which is 0.23″. The [[https://de.wikipedia.org/wiki/Rayleigh-Kriterium|Rayleigh criterion]] describes the theoretical limit at which two Airy discs can be recognized as separated light sources. 
  
-The lower 3 panels of the //Camera Control// window can display various information about the connected cameras as well as statistical information about the images. To switch between the different display modes, you can simply right-click in one of these panels. The right and middle panels are reserved for the cameras, while the left panel can display graphics that show qualitative information about the focus. If no guiding camera is used, the following settings are recommended: left: ''3D Profile'' or ''FWHM/time'', middle: ''Camera 1 Info'' and right: ''Camera 1 Stats''. +{{ :ost:software:nina_autofocus_options.png?nolink&1200 |}}
  
-{{ ost:software:maximdl:focuss_maximdl_6.png |}}+=== PWI 4 ===
  
-The information from the left and right panel is derived from the brightest star in the field of view. The ''3D Profile'' is a 3D view of the image of this star, with the intensity being the third axis. ''FWHM/time'' shows the Full-width Half Maximum (FWHM) of this star as a function of time. The right panel shows the following information: the position of the brightest pixel in X and Y direction, the value of this pixel, the FWHM of the brightest star, the Half Flux Diameter (HFD) of this star, and the Signal to Noise Ratio (SNR).+//PWI4// also offers the possibility of automatic focusing. For this purpose, //PWI4// can connect to //ASCOM// camera drivers. The corresponding setting can be changed in the ''Camera'' tab of the settings dialog. Set **Selected device** to ''ASCOM camera'' and select the corresponding camera driver from the **ASCOM driver** drop-down menu.
  
-As an indication of a good focus, the value of the brightest pixel, the FWHM, the HFD and the SNR can be used. The higher the value in the brightest pixel, the better the SNR, the smaller the FWHM and HFD, the better the focus. It is therefore important to optimize these values during the focusing process. In this respect, the different graphics in the lower left panel can be very helpful, since those illustrate the temporal course.+Afterwards, the autofocus settings can be adjusted in the **Auto Focus** section of the **Focus** tab in the main window of //PWI4//. The parameter ''Images'' defines the number of focusing steps. ''Spacing'' specifies the step size in micrometers that the EFA moves between individual steps. The exposure time and binning must be specified under ''Exp length'' and ''Binning'', respectively.
  
-The middle panel again summarizes the current information about the camera, e.g. if a image acquisition is currently running, which exposure time is set, the selected filter, if the cooling is running and if so, the current and target temperature of the sensor.  +The following settings have proven useful:
  
-==== Subframes ====+    Images     = 17 
 +    Spacing    = 150 
 +    Exp length = must be chosen depending on the object/filter (6 s for stars using the clear filter is a good starting value) 
 +    Binning    = 2
  
-Subframes bieten die Möglichkeit das Auffinden der optimalen Einstellungen für den Fokus deutlich zu beschleunigen. Indem nur ein kleiner Bereich der CCD, welcher selbst gewählt werden kann, ausgelesen wird, kann die Auslesezeit und auch die Downloadzeit stark reduziert werden. 
  
-Der Subframe-Modus kann durch ein Klick auf ''On'' im Bereich //Subframe// aktiviert werden. Nun kann der auszulesende Bereich entweder direkt eingegeben oder per Maus definiert werden. Für Ersteres muss man auf die Zeile mit ''X: Y: W: H:'' klicken. In dem sich öffnenden Fenster kann dann der ''X''- und ''Y''-Wert des Startpixels, sowie die Breite (''Width'') und die Höhe (''Height'') des auszulesenden Kastens angeben werden. Ist die Option ''Mouse'' aktiviert kann mittels der Maus ein entsprechender Kasten auch direkt um einen Stern oder eine Sternengruppe gezogen werden. Dafür muss natürlich erst einmal ein Bild aufgenommen werden ;-) Der Kasten kann durch klicken auf den Rand auch verschoben und durch klicken auf die Ecken in der Größe angepasst werden. **Achtung:** Sollte die Fokussreihe bereits laufen muss diese einmal gestoppt und wieder gestartet werden, damit der Subframe-Modus Wirkung zeigt. +{{ ost:focusser:pwi4_main_window_auto_focus.jpg?800 |}} 
 + 
 +<WRAP center round todo 60%> 
 +The following needs a revision... 
 +</WRAP> 
 + 
 +After starting the autofocus routine, //PWI4// performs the individual focusing steps, moves the EFA by the value specified in ''Spacing'', and takes one image at each position. Afterwards, //PWI4// starts the program //PlateSolve//, which analyzes each image, searches for stars, determines their diameters, and estimates the focus quality. The results are then listed in a table. 
 + 
 +{{ ost:software:maximdl:autofocus_good_3.png |}} 
 + 
 +In the following we show an example of a successful and an unsuccessful autofocus run: 
 + 
 +== Successful autofocus: ==
  
 <WRAP group> <WRAP group>
-<WRAP half column> +<WRAP third column> 
-{{ ost:software:maximdl:focus_maximdl_3.png |}}+[{{ ost:software:maximdl:autofocus_good_6.png | Table with the results }}]
 </WRAP> </WRAP>
-<WRAP half column> +<WRAP third column> 
-{{ ost:software:maximdl:focus_maximdl_4.png |}}+[{{ ost:software:maximdl:autofocus_good_5.png | Plot visualizing the quality of the focus (V-curve plot) }}] 
 +</WRAP> 
 +<WRAP third column> 
 +[{{ ost:software:maximdl:autofocus_good_4.png | Result: well-focused star }}]
 </WRAP> </WRAP>
 </WRAP> </WRAP>
  
-{{ ost:software:maximdl:focus_maximdl_5.png |}}+== Unsuccessful autofocus: ==
  
-**ToDO: Aufnahmen ersetzen!**+<WRAP group> 
 +<WRAP third column> 
 +[{{ ost:software:maximdl:autofocus_bad_2.png | Table with the results }}] 
 +</WRAP> 
 +<WRAP third column> 
 +[{{ ost:software:maximdl:autofocus_bad_1.png | Plot visualizing the quality of the focus (V-curve plot) }}] 
 +</WRAP> 
 +<WRAP third column> 
 +[{{ ost:software:maximdl:autofocus_bad_3.png | Result: poorly focused star }}] 
 +</WRAP> 
 +</WRAP>
  
-===== Mittels CCDOPS =====+There are several reasons why an autofocus run can fail. One reason is that the optimal focus lies outside the range covered by the autofocus routine. It is therefore recommended to roughly focus the telescope manually beforehand. Another possibility is that no stars are detected and the focus quality cannot be estimated.
  
-In diesen Abschnitt gehen wir nur auf die technischen Details ein, welche die Fokussierung mittels //CCDOPS// von der mittels //MaximDL// unterscheidet. Die Grundfunktionen von //CCDOPS// wurden bereits im Hauptartikel zu [[de:ost:ccds:ccdops|CCDOPS]] eingeführt.+===== The traditional approach ===== 
 +<WRAP center round todo 60%> 
 +Replace images... 
 +</WRAP>
  
-Zum Fokussieren der jeweiligen CCD-Kamera nutzt man die Funktion **Focus** im Camera-Menü. 
  
-<code> Camera -> Focus</code>+The traditional method of focusing involves observing a region of the sky that contains a large number of closely packed stars, such as a globular cluster. Under such conditions, the quality of the focus can be judged easily by determining the focus position that allows the largest number of these stars to be resolved individually.
  
-{{ :ost:ccds:ccdops:focus.jpg?direct |}}+For this approach, //Maxim DL// is the most user-friendly software because it offers the most diagnostic tools by default. However, the most important quantities can also be found in the **Statistics** section of the Imaging tab in //N.I.N.A//. In the following, we focus on //Maxim DL//.
  
-Die Einstellungen sollten wie auf den linken Bild seien. Mit dieser Funktion wird wiederholt eine Aufnahme mit einer gewissen Belichtungszeit (''Exposure Time'') in diesem Beispiel von 0.5s gemacht. Die Aufnahmen werden automatisch geladen und dargestellt. Nun kann das Teleskop mittels //CW3// oder des Handterminals für den Okularauszug fokussiert werden.+=== Maxim DL main controls ===
  
-==== Planet Mode ====+In the **Exposure Tab** of the **Camera Control** window (see below), select ''Focus'' in the **Exposure Preset** drop-down menu. In this preset many settings important for focusing are already preselected.
  
-{{ ost:ccds:ccdops:planet_mode_info.jpg|}}+In the examples shown below the exposure time (''Seconds'') is set to one second. This value must be adjusted according to the object used for focusing.
  
-Der Planet Mode folgt den gleichen Prinzipien, die die Subframe-Option bei //MaximDL//. Aufgerufen wird der Planet Mode indem in dem Auswahlmenü für den Fokus (siehe obige Abbildung) der Menüpunkt ''Frame size'' auf **Planet Mode** gesetzt wird. Ist die Fokusreihe bereits gestartet kann diese über den ''Pause''-Button in dem Statusmenü (siehe Abbildung rechts) unterbrochen werden und der Planetmodus über das Drop-down-Menü (''Frame'') ausgewählt werden. Über den ''Resume''-Button kann die Fokusreihe anschließend fortgesetzt werden.+{{ ost:software:maximdl:focus_maximdl_1.png |}}
  
-[{{ ost:ccds:planet_mode_prepare.jpg?550 |Zehn sekündige Aufnahme des Kugelsternhaufens M13 mit Auswahlfenster (kleines weißes Rechteck)}}]+After clicking ''Start'', images are continuously taken and displayed. The telescope can now be focused using //PWI4// or the hand terminal of the EFA. To find the coarse focus, it is recommended to first point the telescope at a bright star and adjust the focus until the diffraction ring disappears.
  
-Hat man eine Fokusreihe im Planet Mode gestartet, wird zuerst eine Aufnahme in voller Auflösung erstellt und auf dem Bildschirm dargestellt. Auf dieser Aufnahme kann man den Subframe auswählen, welcher anschließend im Rahmen der Fokusreihe ausgelesen und dargestellt wird. Die Größe des Subframe kann über das kleine weiße Rechteck definiert werden. Die Größe dieses Rechtecks lässt sich über die kleinen Kästchens in der oberen linken und unteren rechten Ecke anpassen. Der Subframe sollte so gewählt werden, dass möglichst viele nahe beieinander liegende Punktquellen enthalten sind.+To further optimize the focus, a globular cluster can be observed. The small angular separation between the stars in a globular cluster allows very precise focusing, because the Airy disks of individual stars can only be separated with a very well-focused telescope.
  
-Der Fokus kann jetzt bequem und relativ zügig verbessert werden. Als Anhaltspunkt für die Qualität der aktuellen Fokuseinstellung kann auch die maximale Countzahl (''Peak'') herangezogen werden, die dem Statuspannel entnommen werden kann. Je besser die Fokussierung desto höher ist die Countzahl. Dabei muss allerdings beachtet werden, dass Schwankungen bis zu einer Größenordnung von 30% in aufeinanderfolgenden Aufnahmen aufgrund des Seeings völlig normal sind. +An optimally focused telescope operates at the seeing-limited resolution, which at our site is often larger than 2″. This is significantly worse than the diffraction-limited resolution of our telescope, which is about 0.3″. The [[https://de.wikipedia.org/wiki/Rayleigh-Kriterium|Rayleigh criterion]] describes the theoretical limit at which two Airy disks can still be recognized as separate light sources.
  
-Die beiden Aufnahmen unten geben Aufschluss über die Verbesserungen, welche bei relativ schlechtem Seeing zu erreichen sind. +The lower three panels of the **Camera Control** window can display various information about the connected cameras as well as statistical information about the images. The display mode can be changed by right-clicking on one of the panels.
  
-<WRAP GROUP> +If no guiding camera is used, the following configuration is recommended:
-<WRAP half column> +
-[{{ ost:ccds:planet_mode_defocus.jpg |Subframe bevor die Fokussierung optimiert wurde}}] +
-</WRAP> +
-<WRAP half column> +
-[{{ ost:ccds:planet_mode_focus.jpg |Subframe mit optimierter Fokussierung}}] +
-</WRAP> +
-</WRAP>+
  
-/* +  * left panel: ''3D Profile'' or ''FWHM/time'' 
-Ein weiteres Beispiel ist folgender offener Sternhaufen:+  * middle panel: ''Camera 1 Info'' 
 +  * right panel: ''Camera 1 Stats''
  
-[{{ ost:ccds:planet_mode_prepare_2.jpg?550 |Offener Sternhaufen mit Auswahlfenster (kleines weißes Rechteck)}}]+{{ ost:software:maximdl:focuss_maximdl_6.png |}}
  
-<WRAP GROUP>+The information in the left and right panels refers to the brightest star in the field of view. 
 + 
 +The ''3D Profile'' shows a three-dimensional representation of the brightes star, with the intensity representing the third axis. ''FWHM/time'' shows the Full Width at Half Maximum (FWHM) of this star as a function of time. 
 + 
 +The right panel shows: 
 + 
 +  * the position of the brightest pixel in X and Y 
 +  * the pixel value 
 +  * the FWHM 
 +  * the Half Flux Diameter (HFD) 
 +  * the Signal-to-Noise Ratio (SNR) 
 + 
 +Indicators of good focus are: 
 + 
 +  * a high pixel value 
 +  * a high SNR 
 +  * a small FWHM 
 +  * a small HFD 
 + 
 +These values should be optimized during the focusing process. 
 + 
 +=== Maxim DL Subframes === 
 + 
 +Subframes make it possible to significantly speed up the focusing process. Only a small area of the CCD is read out, which can be selected by the user. This greatly reduces the readout and download times. 
 + 
 +The subframe mode can be activated by clicking ''On'' in the **Subframe** section. 
 + 
 +The area to be read out can either be entered directly or defined with the mouse. 
 + 
 +<WRAP group>
 <WRAP half column> <WRAP half column>
-[{{ ost:ccds:planet_mode_defocus_2.jpg?250|Subframe ohne optimierte Fokussierung}}]+{{ ost:software:maximdl:focus_maximdl_3.png |}}
 </WRAP> </WRAP>
 <WRAP half column> <WRAP half column>
-[{{ost:ccds:planet_mode_focus_2.jpg?250 |Subframe mit optimierter Fokussierung}}]+{{ ost:software:maximdl:focus_maximdl_4.png |}}
 </WRAP> </WRAP>
 </WRAP> </WRAP>
-*/ 
  
-===== Fokusierhilfen =====+{{ ost:software:maximdl:focus_maximdl_5.png |}}
  
-==== Lochblenden ====+==== Aperture masks ====
  
-Lochblenden haben sich in der Astrophotographie als Fokussierhilfen und zum Test der Abbildungsqualität von Teleskopen bewährt. Lochblenden mit zwei Öffnungen bezeichnet man in der Regel als Scheinerblende, wohingegen Lochblenden mit mehr als zwei Öffnungen als Hartmannblende bezeichnet werden. Angebracht werden Lochblenden vor der Öffnung des Teleskops. +[{{ ost:telescope:scheinerblende_wiki.jpg?400|Scheiner mask as used in the lab course}}]
  
-[{{ ost:telescope:scheinerblende_wiki.jpg?400|Scheinerblende wie sie für das Praktikum zur Verfügung steht}}]+Aperture masks have proven to be very useful tools in astrophotography for focusing and for testing the optical quality of telescopes. They use the physical principle of diffraction to determine the exact focus position of a telescope.
  
-Zur Fokussierung wird das Teleskop auf eine helle Lichtquelle (z.B. einen hellen Stern) gerichtet. Da das Licht, welches durch die unterschiedlichen Öffnungen der Lochblende fällt, an verschiedenen Punkten die Ebenen vor und hinter der Fokalebene passieren sind mehrere Abbildungen der Lichtquelle zu erkennen, falls das Teleskop defokussiert ist. Durch anpassen des Fokus können die mehrfachen Abbildungen zum überlappen gebracht und schlussendlich zu einer Punktquelle vereinigt werden. Hat man dies erreicht kann man davon ausgehen, dass man den optimalen Fokus gefunden hat. +Masks with two apertures are usually called **Scheiner masks**, whereas masks with more than two apertures are called **Hartmann masks**. The masks are mounted in front of the telescope aperture.
  
-=== Scheinerblende ===+To find the focus, the telescope is pointed at a bright light source (e.g. a bright star). Because the light passes through different apertures, several images of the source appear when the telescope is defocused. By adjusting the focus, these images gradually overlap and finally merge into a single point.
  
-Für das Praktikum steht bisher eine Scheinerblende mit rechteckigen Öffnungen zur Verfügung, bei der einer diese Öffnungen um 45° gegen die andere gedreht ist (siehe rechte Abbildung). Diese Lochmaske hat den Vorteil, dass aufgrund der Beugung an den Öffnungen die Abbildungen des zu fokussierenden Objektes jeweils mit Spikes überlagert sind, welche entsprechen der Drehung der Öffnungen ebenfalls um 45° gegeneinander verschoben sind. Die Spikes sind eine gute Hilfestellung bei fokussieren, da diese nur bei idealer Fokussierung ein symmetrisches "Sternchen" bilden (siehe Abbildung unten). Eine Vorlage der beschriebene Scheinerblende im A2-Format für das C14 von Celestron ist {{ost:telescope:scheinerblende.pdf|hier}} zu finden.+=== Scheiner mask ===
  
-[{{ost:ccds:scheinerblende_complete.jpg?815|Testaufnahmen eines hellen Sterns erstellt mit der Scheinerblende (von links nach rechts zunehmend bessere Fokussierung)}}]+For some of our telescopes we have Scheiner masks with rectangular apertures that are rotated by 45° relative to each other. This produces diffraction spikes that are also rotated by 45°. These spikes are a useful aid when focusing because they form a symmetric pattern only when the telescope is properly focused.
  
-=== Bathinovblende ===+A template of the described Scheiner mask (A2 format) for the C14 from Celestron can be found {{{ost:telescope:scheinerblende.pdf|here}}}. 
 + 
 +[{{ost:ccds:scheinerblende_complete.jpg?815|Test exposure of a bright star using a Scheiner mask (focus improves from left to right)}}] 
 + 
 +=== Bahtinov masks === 
 + 
 +A Bahtinov mask contains three sets of slits oriented at different angles. When observing a star, this produces a characteristic diffraction pattern with three spikes. 
 + 
 +Two spikes remain relatively fixed, while the central spike shifts depending on the focus position. When the focus is adjusted so that this spike lies exactly between the other two, the optimal focus has been reached. 
 + 
 +<WRAP center round todo 60%> 
 +Add images... 
 +</WRAP>
  
-Kommt noch! 
  • en/ost/fokus_new.1599766028.txt.gz
  • Last modified: 2020/09/10 19:27
  • by rhainich