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en:ost:fokus_new [2020/09/10 20:29] – [Fokusierhilfen] rhainichen:ost:fokus_new [2023/12/06 13:30] (current) – [General remarks] 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 ======
  
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 ++++ 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 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:
  
    D = 147 − 12,5 − 33/2 - C,    D = 147 − 12,5 − 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 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.
 ++++ ++++
  
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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                  |  20+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     |  17000  | 
-| Canon + Superzoom        |  100    |  19550  |+| Hyperionokular: 36mm      |  80     |  14500  | 
 +| Hyperionokular: 22mm      |  80     |         | 
 +| Hyperionokular: 13mm      |  80     |  25200  | 
 +| Canon + Superzoom         |  80     |  19550  |
  
 ==== Manually ==== ==== Manually ====
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 //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: //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:
  
-    Step Size (micron)    = 500 +    Step Size (micron)    = 150 
-    Steps (Image Count)   = 5+    Steps (Image Count)   = 17
     Exposure length (sec) = must be chosen depending on the object     Exposure length (sec) = must be chosen depending on the object
  
-**ToDo: More to come!**+{{ ost:software:maximdl:autofocus_good_3.png |}} 
 + 
 +After starting the auto focus, //PWI3// will perform the individual focusing steps, move the EFA by the ''Step Size'' and take one image at a time. Afterwards, //PWI3// 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 the following we show an example of a successful and an unsuccessful auto focus run: 
 + 
 +== Successful auto focus: ==  
 + 
 +<WRAP group> 
 +<WRAP third column> 
 +[{{ ost:software:maximdl:autofocus_good_6.png | Table with the results }}] 
 +</WRAP> 
 +<WRAP third column> 
 +[{{ 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> 
 + 
 +== Unsuccessful auto focus: ==  
 + 
 +<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> 
 + 
 +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. 
  
 ===== Using MaximDL ===== ===== Using MaximDL =====
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 </WRAP> </WRAP>
  
-===== Aperture diaphragms =====+===== Focusing aids =====
  
-==== 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. +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|Scheinerblende wie sie für das Praktikum zur Verfügung steht}}]+[{{ ost:telescope:scheinerblende_wiki.jpg?400|Scheiner mask, like it is available for the lab course}}]
  
-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. +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.
  
-=== Scheinerblende ===+=== Scheiner mask ===
  
-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.+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}}.
  
-[{{ost:ccds:scheinerblende_complete.jpg?815|Testaufnahmen eines hellen Sterns erstellt mit der Scheinerblende (von links nach rechts zunehmend bessere Fokussierung)}}]+[{{ost:ccds:scheinerblende_complete.jpg?815|Test exposure of a bright star employing a Scheiner mask (improved focus from left to right)}}]
  
-=== Bathinovblende ===+=== Bathinov masks ===
  
-Kommt noch!+Comming soon!
  • en/ost/fokus_new.1599769795.txt.gz
  • Last modified: 2020/09/10 20:29
  • by rhainich