Alcor NOVA 120 User Manual
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Alcor NOVA 120 User Manual

Direct drive equatorial mount pointing model user manual
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Direct Drive Equatorial Mount
NOVA 120
Pointing model user manual
NOVA 120 Pointing model user manual
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  • Page 1 Direct Drive Equatorial Mount NOVA 120 Pointing model user manual NOVA 120 Pointing model user manual...
  • Page 2 Here is a list of Acronym used in this document Acronym Meaning Right ascension Declination This is a standard formalism used for achieving pointing model, TPOINT see here for more information http://www.tpsoft.demon.co.uk/pointing.htm Hour angle, or meridian angle MA or HA http://en.wikipedia.org/wiki/Hour_angle NOVA 120 Pointing model user manual...

  • Page 3: Table Of Contents

    Calibrating the first field ..........................18 2.3. Sweep the sky with fields, and build pointing model field list ..............19 Applying the pointing model to the NOVA mount ......................42 Final checks ................................... 44 NOVA 120 Pointing model user manual...

  • Page 4: Introduction

    The next picture shows what happens with a poorly polar mount alignment (18 arcmin error from the pole) and a 600s unguided exposure. NOVA 120 Pointing model user manual...
  • Page 5 Even, more the next picture shows a raw single 900s unguided exposure that would be impossible to achieve without the speed model and refraction speeds compensations. NOVA 120 Pointing model user manual...

  • Page 6: Achieving Pointing Model Files

    The type of file format to provide to the NOVA mount software is a simple “*.cor” file, which is indeed a simple text file. Here is a “.cor” file sample; always starting with 789955491 as a magic number. Then pointing model coefficients expressed in radians are listed after: NOVA 120 Pointing model user manual...
  • Page 7 When performing the pointing model with other software than PRISM, do not forget to disable any pointing model at the NOVA mount software level. Finally keep in mind that the NOVA mount software sends to the ASCOM client software “Observed coordinates” that are corrected from refraction and not “Topocentric place” coordinates. NOVA 120 Pointing model user manual...

  • Page 8: Using Prism Software To Get Pointing Model Coefficients

    Before starting the NOVA mount software, please ensure that any pointing model is already enabled, if so disable it. Go here: Uncheck this checkbox, if checked: When the mount is running and connected to the software, it will mention that the pointing model is disabled, as shown hereafter: NOVA 120 Pointing model user manual...
  • Page 9 Go to “Setup” then “System setup”, press “German mount setup” and change as follows the allowable mount clearance. NOVA 120 Pointing model user manual...

  • Page 10: Plate Solving Checking

    Using PRISM software from ALCOR-SYSTEM, please, connect the mount to PRISM, and keep eye on side of pier information that is sent by the NOVA mount software to PRISM. This panel helps doing so: Say, that the pointing model will be built for the telescope located on the east side of the pier, aiming at targets that are on the west side of the Sky.
  • Page 11 Slew to a star that can be identified with the sky map, which is not too bright, and be sure this star is located into the camera’s field of view. The next image shows the star and the sky map that matches to it. Then re-center the star so that it is located at the image’s center. NOVA 120 Pointing model user manual...
  • Page 12 “calibrate with” button. Then the Sky map and the telescope are now synchronized. Then now acquire another image, this image will have the proper rough RA/DEC coordinates that will be used for plate solving. Be sure to be focused as best as possible. NOVA 120 Pointing model user manual...
  • Page 13 Then now select this menu: This form sets the parameters to be used for automatic plate solving. NOVA 120 Pointing model user manual...
  • Page 14 Do put a valid focal length (10% error is allowed). The catalog used for plate solving is important, use either GSC-ACT star catalog or UCAC 2/3/4 catalog. These star catalogs are available for free on download here: http://www.prism-astro.com/us/catalogs.html UCAC 4 is recommended, but it works also well with GSC-ACT catalog. NOVA 120 Pointing model user manual...
  • Page 15 A combination of failures above will result in failure, they do not compensate, so go step by step. Failure to achieve PRISM’s plate solving will result in pointing model failure, so this is a mandatory step and need to work out! NOVA 120 Pointing model user manual...
  • Page 16 If you go back into the camera setup form, the focal length can be updated. The camera orientation can be also been entered in this case, this has no function for achieving the pointing model, but can be convenient for other purposes. NOVA 120 Pointing model user manual...
  • Page 17 This “other purpose” is to use telescope shift with the mouse. Left click over the image and then use “Shift telescope” NOVA 120 Pointing model user manual...

  • Page 18: Calibrating The First Field

    This not a mandatory step to make functional the pointing model, but is very useful. Now, you are ready to create your first point model. 2.2.3. Calibrating the first field NOVA 120 Pointing model user manual...

  • Page 19: Sweep The Sky With Fields, And Build Pointing Model Field List

    East side of the sky, thus meridian angle http://en.wikipedia.org/wiki/Hour_angle is from minus 12H to 0H. PRISM embeds a feature that will allow sweeping across the sky, and allowing you to carry out the pointing model. Click to this menu: NOVA 120 Pointing model user manual...
  • Page 20 This form should appear, and is the control panel that will allow you to build the pointing model field list. NOVA 120 Pointing model user manual...
  • Page 21 This can happen when the mount is really not well polar aligned or optical axis and DEC axis errors exceeds more than 30’ (indeed has poor pointing performance). NOVA 120 Pointing model user manual...
  • Page 22 The sky map is populated with blue dots, with corresponding field’s number. There are many more fields nearby the pole because meridian lines distances are getting closer (because distance is divided by cosine of DEC). NOVA 120 Pointing model user manual...
  • Page 23 Then press “Startup”, and the telescope will slew toward all the 50 fields, one after the other, and will perform plate solving for each. NOVA 120 Pointing model user manual...
  • Page 24 When a field is completed, the sky map label turns into red, actual and expected coordinates are filled, as well as distance from actual to expected position. For instance, field #1, error distance is 5.9 arcmin, it found plate solving after 1 trial (Tests column), and plate solving residual are just 0.01 pixel. NOVA 120 Pointing model user manual...
  • Page 25 If plate solving fails, the error is reported in the list, this field will not be used to build the pointing model file and telescope slews to the next field. This can happen if the field is too close to the moon or if clouds are present in this location. NOVA 120 Pointing model user manual...
  • Page 26 Important: mount meridian flip should never occur during this process! Otherwise pointing model will not be valid. Just watch from time to time that the process goes well, and during it you can have a cup of coffee, and let it running. NOVA 120 Pointing model user manual...
  • Page 27 Nevertheless, it those failed fields are located at the same place of the sky; this is not good and can lead to poor pointing model. Investigate the cause of these failures and try to solve them. NOVA 120 Pointing model user manual...
  • Page 28 After field list coordinates have been saved, this form appears, and will allow you to build the pointing model file. The same list is displayed: expected/theoretical positions and actual/measured positions. This is “observed place” coordinates system. Then click to “Compute” tab. NOVA 120 Pointing model user manual...
  • Page 29 19.6 arcsec RMS error is been now achieved, using this set of enables / disables. This is a very good performance, because the RMS pointing error has been reduced from 5 arcmin (600 arcsec) down to 19.6 arcsec which is a ratio of 30.6 fold! NOVA 120 Pointing model user manual...
  • Page 30 In the “Plots” tab, various errors can be plotted. The residuals point errors before and after the pointing model is really interesting. Here is after before, where point are really spread. NOVA 120 Pointing model user manual...
  • Page 31 The “after pointing model” residual shows that the position error for each field is random. It has been reduced by 30x and can fit a RA -20 / +20 arcsec and DEC -40 / +40 arcsec box! Even more impressive is the “Projection errors” tab showing errors before and after pointing model NOVA 120 Pointing model user manual...
  • Page 32 Use horizontal slide bar to zoom into error for each field, and check/uncheck “Pointing model benefits”. In this example, the improvement is rather impressive. Also the error vector is random, meaning that the pointing model fitting is rather suitable. NOVA 120 Pointing model user manual...
  • Page 33 Any name can be used, but a meaningful name is recommended such as: TubeWestPier-10-10-14.cor We recommend putting into the file name the side of the tube used for building this model. Later, the explanation of this trick will be described. NOVA 120 Pointing model user manual...
  • Page 34 For German mounts, the same procedure shall be applied onto the other side of the sky. Do not synchronize the mount; just perform a slewing to the next side of the sky. The mount will then perform mount flip. NOVA 120 Pointing model user manual...
  • Page 35 This can be carried out by left click of the mouse where the telescope is going to be at end slewing (red arrow on next screen capture). NOVA 120 Pointing model user manual...
  • Page 36 The mount will slew and perform a meridian flip to the destination coordinates. On slew ending, the telescope’s side of pier will report “East side” NOVA 120 Pointing model user manual...
  • Page 37 Now go back to the control panel, and click “West side of the Sky”. Then click “Create field list”, this will erase and overwrite the previous field list. The blue dots that are representing the fields to be scanned, will change position to the other side of the Sky. NOVA 120 Pointing model user manual...
  • Page 38 The process lasts some minutes, if you have a dome, ensure that the dome is “slaved“ to the telescope, otherwise plate solving error will arise (obscured and missing stars). NOVA 120 Pointing model user manual...
  • Page 39 As you can notice, pointing errors are increased compared to the other side of the Sky. This is normal, because DEC mount axis and telescope optical axis are never perfectly perpendicular, and this error leads to large errors when mount is meridian flipped. NOVA 120 Pointing model user manual...
  • Page 40 At the end of the process, the same form will appear, and you have to proceed the same way with. NOVA 120 Pointing model user manual...
  • Page 41 Do not forget to save the resulting “.cor” file as (for instance): TubeEastPier-10-10-14.cor This is interesting to look at differences between west and east side of pier models: Side of pier : West Side of pier : East NOVA 120 Pointing model user manual...

  • Page 42: Applying The Pointing Model To The Nova Mount

    Then to the NOVA mount software, go to setup then open the pointing model setup form: Enable pointing model and select the TubeWestPier-10-10-14.cor and TubeEastPier-10-10-14.cor accordingly. So having named the files this way is a good trick to avoid mixing up these files. NOVA 120 Pointing model user manual...
  • Page 43 Then connect to the mount hardware, and notice that pointing model is enabled, also speed model is enabled: If the “+” button is clicked, a status window appears and shows the current status of pointing/speed model. NOVA 120 Pointing model user manual...

  • Page 44: Final Checks

    Sky, targets will be inside the field of view of the camera. Also same checking can be performed by long unguided exposures with speed model enabled. NOVA 120 Pointing model user manual...
  • Page 45 For a mobile telescope, this has to be performed each time the telescope is moved. In the latter case, it is not required, but mount performance will be degraded and since it just takes one hour to be achieved, it is worth the effort. NOVA 120 Pointing model user manual...

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