Differences

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--- en:ost:fokus_new [2025/10/03 08:28] – jsiehr
+++ en:ost:fokus_new [2026/03/10 13:29] (current) – rhainich
@@ Line 1: / Line 1: @@
 ====== Focusing ======
-<WRAP center round important 40%>
+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.
-Please note that this article is currently being updated.
-</WRAP>
-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.
 ===== 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 |
-The back focus of the telescope is 147 mm (behind the EFA). The Zeiss quick changer used has a back focus of 25 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 − 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 50mm 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.
 ++++
@@ Line 31: / Line 26: @@
 | Baches + QHY268M + Barlow |  20     |  17500  |
 | DADOS + QHY268M           |   0     |  5000   |
-| Hyperionokular: 36mm      |  80     |  14500  |
+| Hyperion eyepiece: 36mm   |  80     |  14500  |
-| Hyperionokular: 22mm      |  80     |         |
+| Hyperion eyepiece: 22mm   |  80     |         |
-| Hyperionokular: 13mm      |  80     |  25200  |
+| 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 half column>
+<WRAP third column>
 <imgcaption handterminal|Hand terminal for the EFA>{{ :ost:focusser:focusser_handcontroller_1.png?300 }}</imgcaption>
 </WRAP>
-<WRAP half column>
+<WRAP third column>
-\\
-\\
-\\
-\\
-\\
-\\
 <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>
-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 //PWI4//, 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?1000|PWI4: Focus window including temperature display}}
-The operation of the EFA is basically self-explanatory. The current position can be found in the field ''Position'', while the EFA can be moved via the buttons ''IN'' and ''OUT''. The speed of the focuser can set under "Jog", by inputting a value next to it. We recommend the standard setting of 200 micron/s. 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.
+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.
+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.
 ==== Auto Focus ====
-In general it is not feasible to focus manually, unless a specific focus point is already known from e.g. previous observations. Therefore automatic focus methods can be found in several programs. Here we shall list focusing using PWI4, MaximDL, NINA and others. Whichever program is used depends on the observers preferences and target.
-=== Using PWI 4 ===
+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.
-//PWI4// also offers the possibility of automatic focusing. For this purpose, //PWI4// 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)    = 150
+<WRAP center round todo 60%>
-    Steps (Image Count)   = 17
+This part needs to be written.
-    Exposure length (sec) = must be chosen depending on the object/filter (6s for stars using clear filter is a good start)
+</WRAP>
-{{ ost:software:maximdl:autofocus_good_3.png |}}
+=== NINA ===
+{{:ost:software:nina_autofocus_start.png?nolink&300 | NINA Autofocus}}
-After starting the auto focus, //PWI4// will perform the individual focusing steps, move the EFA by the ''Step Size'' and take one image at a time. Afterwards, //PWI4// will start the program //PlateSolve// (see above), which will analyze each image, search for stars, determine the diameter of these stars and estimate the focus. This is then listed in a table. With a click on ''Show Graph'' you can visualize the result. The determined star diameter is displayed over the position of the eyepiece extension. In the ideal case this representation follows a V-curve, which is also fitted into the data.
+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.
+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.
+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.
+Under ''Options > Autofocus'' the settings for fine-tuning the autofocus can be found. An image of these settings is shown below the documentation.
+  * **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
+{{ :ost:software:nina_autofocus_options.png?nolink&1200 |}}
+=== PWI 4 ===
+//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.
+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 following settings have proven useful:
+    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
+{{ 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 auto focus run:
+In the following we show an example of a successful and an unsuccessful autofocus run:
-== Successful auto focus: ==
+== Successful autofocus: ==
 <WRAP group>
@@ Line 90: / Line 138: @@
 </WRAP>
 <WRAP third column>
-[{{ ost:software:maximdl:autofocus_good_5.png | Plot visualizing the quality of the focus (V curve plot) }}]
+[{{ 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 }}]
+[{{ ost:software:maximdl:autofocus_good_4.png | Result: well-focused star }}]
 </WRAP>
 </WRAP>
-== Unsuccessful auto focus: ==
+== Unsuccessful autofocus: ==
 <WRAP group>
@@ Line 104: / Line 152: @@
 </WRAP>
 <WRAP third column>
-[{{ ost:software:maximdl:autofocus_bad_1.png | Plot visualizing the quality of the focus (V curve plot) }}]
+[{{ ost:software:maximdl:autofocus_bad_1.png | Plot visualizing the quality of the focus (V-curve plot) }}]
 </WRAP>
 <WRAP third column>
@@ Line 111: / Line 159: @@
 </WRAP>
-There are several reasons why a autofocus run can fail. One of them is that the ideal focus is not in the area that is covered by the autofocus run. It is therefore recommended to focus the telescope roughly by hand before. Furthermore, it can be that no star is found and therefore the quality of the focus cannot be estimated. A reason for this may in turn be that the option ''Use a Subframe, Central 1/4 pixels'' was selected during setup and that there is no star in the central area of the chip.
+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.
-=== Using MaximDL ===
+===== The traditional approach =====
+<WRAP center round todo 60%>
+Replace images...
+</WRAP>
-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]].
-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.
+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:software:maximdl:focus_maximdl_1.png |}}
+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//.
-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.
+=== Maxim DL main controls ===
-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.
+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.
-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''.
+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.
-{{ ost:software:maximdl:focuss_maximdl_6.png |}}
+{{ ost:software:maximdl:focus_maximdl_1.png |}}
-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).
+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.
-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.
+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.
-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.
+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.
-==== Subframes ====
+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.
-Subframes offer the possibility to significantly speed up the process of finding the optimal settings for the focus. By reading out only a small area of the CCD, which can be selected by the user, the readout time and also the download time can be greatly reduced.
+If no guiding camera is used, the following configuration is recommended:
-The subframe mode can be activated by clicking on ''On'' in the //Subframe// section. Now the area to be read out can either be entered directly or defined by mouse. For the former you have to click on the line with ''X: Y: W: H:''. In the window that opens, you can then specify the ''X'' and ''Y'' values of the start pixel, as well as the width and height of the box to be read. If the option ''Mouse'' is activated, a box can also be dragged directly around a star or a group of stars with the mouse. Of course you have to take a picture first ;-) The box can also be moved by clicking on the border and resized by clicking on the corners. **Attention:** If the focus series is already running, it must be stopped and restarted for the subframe mode to take effect.
+  * left panel: ''3D Profile'' or ''FWHM/time''
+  * middle panel: ''Camera 1 Info''
+  * right panel: ''Camera 1 Stats''
-<WRAP group>
+{{ ost:software:maximdl:focuss_maximdl_6.png |}}
-<WRAP half column>
-{{ ost:software:maximdl:focus_maximdl_3.png |}}
-</WRAP>
-<WRAP half column>
-{{ ost:software:maximdl:focus_maximdl_4.png |}}
-</WRAP>
-</WRAP>
-{{ ost:software:maximdl:focus_maximdl_5.png |}}
+The information in the left and right panels refers to the brightest star in the field of view.
-**ToDO: replace images!**
+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:
-=== Using NINA ===
+  * the position of the brightest pixel in X and Y
-{{:ost:software:nina_autofocus_start.png?nolink&300 | NINA Autofocus}}
+  * the pixel value
+  * the FWHM
+  * the Half Flux Diameter (HFD)
+  * the Signal-to-Noise Ratio (SNR)
-In NINA the autofocus can be run by selecting ''Imaging'' and then select on the right-hand side autofocus. After selecting autofocus NINA will automatically start the process. Note however, that the focuser needs to be started via PWI4 and equipped via the "Equipment" tab. Furthermore NINA will use whatever filter is currently selected. A successful autofocus run can be seen on the left side, where a clear hyperbolic relation is visible. The run took about 6:30min and determined 6612 as the optimal focus for the clear filter.
+Indicators of good focus are:
-Under "Options>Autofocus" the settings to finetune the autofocus can be found. An image can be seen below the documentation of these settings:
+  * a high pixel value
+  * a high SNR
+  * a small FWHM
+  * a small HFD
-  * **Use filter offsets** Lets you apply predefined offsets per filter instead of refocusing every time. (Currently not available, test observation needed). Default: OFF
+These values should be optimized during the focusing process.
-  * **Autofocus initial offset steps** How far the focuser moves out initially to start the autofocus. Default: 10
-  * **Autofocus method** Self explanatory. Default: Star HFR (Half-Flux Radius of stars)
-  * **Curve fitting strategy** Function to fit your measurement. 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 instead of all detected stars (Good for poor star fields/Noisy images). Default: 0
-  * **Outer crop ratio** 1 crop overscan region, -1 include overscan region. 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** How far the focuser moves between samples. Default: 150
-  * **Default autofocus exposure time** Exposure duration (in seconds) per autofocus frame. Default: 6s, but for clear, needs to be adapted for other filters.
-  * **Disable guiding during AF** Turns off guiding while autofocus runs. Default: off
-  * **Focuser settle time** Delay after a focuser move to allow mechanical settling. Default: 1
-  * **Number of exposures per point** How many frames are taken at each step, then averaged. Default: 1
-  * **Inner crop ratio** Crops the center region of the frame when detecting stars. Default: 0.5 = 50%, can be selected within [0.2,1]
-  * **Backlash compensation method** Overshoot or Disable, to cancel gear play. Default: Not available/Overshoot
-  * **Backlash IN/OUT** Step count used to clear backlash when moving in or out. Default: 20,0
+=== Maxim DL Subframes ===
-{{ :ost:software:nina_autofocus_options.png?nolink&1200 |}}
-===== Ussing CCDOPS =====
-In this section, we will only go into the technical details that distinguish the focus using //CCDOPS// from the focus using //MaximDL//. The basic functions of //CCDOPS// were already introduced in the main article about [[en:ost:ccds:ccdops|CCDOPS]].
-To focus the respective CCD camera, use the **Focus** function in the Camera menu.
-<code> Camera -> Focus</code>
-{{ :ost:ccds:ccdops:focus.jpg?direct |}}
-The settings should be similar to the example shown on the image above. In this operation mode, the camera will repeatedly take images of a certain ''Exposure Time'' (0.5s in the example above). The individual exposures will be automatically downloaded and displayed. Now the telescope can be focused using //CW3// or the hand terminal for the EFA.
-==== Planet Mode ====
-{{ ost:ccds:ccdops:planet_mode_info.jpg|}}
-The Planet Mode follows the same principles as the subframe option of //MaximDL//. The planet mode can be activated by choosing the **Planet Mode** option from the drop down menu ''Frame size'' in the focus menu (see figure above). If the focus series is already running, the plate mode can be activated by pausing the exposures with a click on the ''Pause'' button in the status window (see right figure) and choosing the planet mode from the drop-down menu (''Frame''). Afterwards click on the ''Resume'' button to continue the focus series.
-[{{ ost:ccds:planet_mode_prepare.jpg?550 |Exposure (10s) of a globular cluster M13 with a selection box (small white rectangle)}}]
+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 first exposure of a focus series in planet mode will be a full frame exposure. On this full frame exposure, one can select a subframe that subsequently will be readout and displayed within the scope of the focus series. The subframe is defined by the small white box. The size of this box can be adjusted by means of the (very) small rectangles in the upper left and lower right corner of the box. The subframe should be selected so that as many point sources as possible are contained close together.
+The subframe mode can be activated by clicking ''On'' in the **Subframe** section.
-The focus can then be easily and relative fast adjusted. An indicator for the quality of the focus is also the maximal count number (''Peak'') that can be found in the status panel. The better the focus is, the higher is the maximal count number. However, be aware of the fact that fluctuations of up to 30% in successive exposures are completely normal due to the seeing.
+The area to be read out can either be entered directly or defined with the mouse.
-The two images below show the improvements that can be achieved with poor seeing conditions:
+<WRAP group>
-<WRAP GROUP>
 <WRAP half column>
-[{{ ost:ccds:planet_mode_defocus.jpg |Subframe before the focus was optimized}}]
+{{ ost:software:maximdl:focus_maximdl_3.png |}}
 </WRAP>
 <WRAP half column>
-[{{ ost:ccds:planet_mode_focus.jpg |Subframe with an optimized focus}}]
+{{ ost:software:maximdl:focus_maximdl_4.png |}}
 </WRAP>
 </WRAP>
-===== Focusing aids =====
+{{ ost:software:maximdl:focus_maximdl_5.png |}}
 ==== Aperture masks ====
-Aperture masks have proven their worth in astrophotography as focusing aids and for testing the imaging quality of telescopes. Aperture masks with two apertures are usually called Scheiner apertures, whereas aperture masks with more than two apertures are called Hartmann apertures. Aperture masks are attached in front of the telescope's aperture.
+[{{ ost:telescope:scheinerblende_wiki.jpg?400|Scheiner mask as used in the lab course}}]
-[{{ ost:telescope:scheinerblende_wiki.jpg?400|Scheiner mask, like it is available for the lab course}}]
+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.
-For finding the focus, the telescope needs to be pointed to a bright light source (e.g. a bright star). Since the light that passes through the different apertures of the pinhole passes the planes in front and behind the focal plane at different points, several images of the light source can be seen if the telescope is defocused. By adjusting the focus, the multiple images can be overlapped and finally merged into one point source. Once this has been achieved, one can assume that the optimal focus has been found.
+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.
+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.
 === Scheiner mask ===
-For our telescope, we have a Scheiner mask with rectangular apertures, where the apertures are rotated by 45° against each other (see the right figure). The advantage of this kind of Scheiner masks is that the images of the object are superimposed with spikes, due to diffraction at the apertures. These spikes are shifted by 45° against each other corresponding to the rotation of the apertures. The spikes are a good aid for focusing, since the spikes form a symmetric “starlet” only for a well focused telescope. A template of the described Scheiner diaphragm (A2 format) for the C14 from Celestron can be found {{{ost:telescope:scheinerblende.pdf|here}}.
+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.
-[{{ost:ccds:scheinerblende_complete.jpg?815|Test exposure of a bright star employing a Scheiner mask (improved focus from left to right)}}]
+A template of the described Scheiner mask (A2 format) for the C14 from Celestron can be found {{{ost:telescope:scheinerblende.pdf|here}}}.
-=== Bathinov masks ===
+[{{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>
-Comming soon!