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NOVA 120 Pointing model user manual  

 

 

6 

 

 

 

 

2. Achieving Pointing model files 

  

2.1. 

Data coming from any software (except PRISM software)  

 

In this document, the pointing model will be demonstrated using the PRISM software package. Nevertheless, this is not a 

mandatory step, because other software in the market can use 

TPOINT

 and provide valid data that can be used with the 

mount NOVA software.  The purpose of this document is not to demonstrate how to achieve a pointing model with all 

the software available in the market. We will do it using PRISM, because this is very easy to achieve. 

An important point, for German mounts, there are two pointing models required, one for the tube located at the east 

side of pier, and another for the west side of pier. These models had turned out not to be the same, by experience.  

 

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: 

Содержание NOVA 120

Страница 1: ...NOVA 120 Pointing model user manual 1 Direct Drive Equatorial Mount NOVA 120 Pointing model user manual...

Страница 2: ...ist of Acronym used in this document Acronym Meaning RA Right ascension DEC Declination TPOINT This is a standard formalism used for achieving pointing model see here for more information http www tps...

Страница 3: ...software except PRISM software 6 2 2 Using PRISM software to get pointing model coefficients 8 2 2 1 Prerequisites 8 2 2 2 Plate solving checking 10 2 2 3 Calibrating the first field 18 2 3 Sweep the...

Страница 4: ...right star field of view is 15x15 arcmin but no star is present Right is an image that demonstrates the effect of the pointing model the star is at the image s center Working without a pointing model...

Страница 5: ...will be calculated and applied Despite the poor polar alignment the 600s unguided exposure is perfect because the mount software could compensate for this error automatically based on the pointing mod...

Страница 6: ...how to achieve a pointing model with all the software available in the market We will do it using PRISM because this is very easy to achieve An important point for German mounts there are two pointin...

Страница 7: ...e flexure error 2 6 2 46848043582684E 0004 FO Fork axis flexure error 0 84 1 16523424111638E 0003 DAF DEC axis cantilever error 3 98 5 05908232673203E 0005 DAB DEC axis flexure error 0 174 0 000000000...

Страница 8: ...2 1 Prerequisites 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 a...

Страница 9: ...NOVA 120 Pointing model user manual 9 Go to Setup then System setup press German mount setup and change as follows the allowable mount clearance...

Страница 10: ...YSTEM 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 fo...

Страница 11: ...by matching the star of the image with a catalog Nevertheless this feature shall be checked and shall work otherwise no pointing model can be build Slew to a star that can be identified with the sky...

Страница 12: ...at the mouse is set to identification mode and this window appears click to the calibrate with button Then the Sky map and the telescope are now synchronized Then now acquire another image this image...

Страница 13: ...NOVA 120 Pointing model user manual 13 Then now select this menu This form sets the parameters to be used for automatic plate solving...

Страница 14: ...either from a previous plate solving or from the user when camera was set up Do put a valid focal length 10 error is allowed The catalog used for plate solving is important use either GSC ACT star cat...

Страница 15: ...lving might not work and here it a list and proposed solutions Cause of failure Solution Focal length no set correctly Change focal length do trial and tests The center coordinates are not good Refine...

Страница 16: ...mputed and is accurate to the mm 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 achievi...

Страница 17: ...NOVA 120 Pointing model user manual 17 This other purpose is to use telescope shift with the mouse Left click over the image and then use Shift telescope...

Страница 18: ...star or other object to be inside the image the telescope will slew so that the image is centered as you wish This not a mandatory step to make functional the pointing model but is very useful Now you...

Страница 19: ...red stars and leads to a far better positioning that he could be achieved with a single star So there is no need to center to a single star used as reference and to select some In this document a Germ...

Страница 20: ...NOVA 120 Pointing model user manual 20 This form should appear and is the control panel that will allow you to build the pointing model field list...

Страница 21: ...If northern hemisphere say in the USA theses figures would be from DEC 20 to 80 Meridian angle or hour angle can be from 12H to 12H and since the East side of the Sky checkbox is checked the software...

Страница 22: ...ill help a lot and will avoid getting plate solving failures when located near to the Moon The sky map is populated with blue dots with corresponding field s number There are many more fields nearby t...

Страница 23: ...ith fields and distribution is uniform In case of fork mount a single all sky sweep is sufficient since those kind of mount does not perform any meridian flip Then press Startup and the telescope will...

Страница 24: ...minutes to complete this process using I Core I7 PC 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 po...

Страница 25: ...te 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 m...

Страница 26: ...have been completed and the telescope is slewing to the 16th Important mount meridian flip should never occur during this process Otherwise pointing model will not be valid Just watch from time to tim...

Страница 27: ...e into a text file Save the file as for instance as StarFieldWest_sideofPier Note that in this case none of the fields returned plate solving failed if you have 5 to 10 field failed in random fashion...

Страница 28: ...spected later to understand the cause of failure 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...

Страница 29: ...nting model is 5 0 arcmin There is some improvement but better can be obtained Do some try and test by checking and unchecking mount errors checkboxes and the press Compute to evaluate the result 19 6...

Страница 30: ...inting model user manual 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 rea...

Страница 31: ...ting 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 erro...

Страница 32: ...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...

Страница 33: ...internal description is given into 1 Click Save result file cor a save dialog appears Any name can be used but a meaningful name is recommended such as TubeWestPier 10 10 14 cor We recommend putting...

Страница 34: ...not close the form that controls the recording sweeping of fields For German mounts the same procedure shall be applied onto the other side of the sky Do not synchronize the mount just perform a slew...

Страница 35: ...NOVA 120 Pointing model user manual 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...

Страница 36: ...NOVA 120 Pointing model user manual 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...

Страница 37: ...ck 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 w...

Страница 38: ...o CANCEL the process and Avoid fields to be too close to the meridian Be sure about the NOVA mount setting and what cause the meridian flip go above into this documentation on how to overcome this The...

Страница 39: ...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 t...

Страница 40: ...NOVA 120 Pointing model user manual 40 At the end of the process the same form will appear and you have to proceed the same way with...

Страница 41: ...user manual 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...

Страница 42: ...ing two models is always employed by professionals Pointing model is really powerful to extract what is happening to the whole setup telescope mount and sometime can help to apply fixes polar alignmen...

Страница 43: ...pointing model will produce twice the error of no pointing model Then connect to the mount hardware and notice that pointing model is enabled also speed model is enabled If the button is clicked a st...

Страница 44: ...ill not jeopardize point model performance Then the same procedure of field scans can be achieved in both sky hemispheres before and after meridian to check how the pointing model is actually improvin...

Страница 45: ...be achieved once every year or every two years for a fixed telescope 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 p...

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