Re: Cannot get autoguding to work at all #iEXOS-100 #TECHNICAL

Wes Mcdonald


When you do a go-to the mount goes to the target and is in point mode. In point mode the mount will maintain the scope pointing  at the correct place in the sky by moving both the Ra and dec axis.  If the scope were exactly mechanically polar aligned then the Dec would not need to move.  With a mount that is not mechanically  polar aligned but for which a 2 or 3 star alignment is made the point mode will keep the scope, by using the alignment model, pointing directly at the object Ra and dec.  However when you center the target the mount leaves point mode and enters track mode.   In track the scope only moves the ra axis at sidereal basically assumes the mount is polar aligned.  Thus no dec movement is called for.  If the mount is not mechanically polar aligned but in track mode a centered object will appear to drift out.

In the past and presently the only way to resume point mode was to either perform a goto again or direct the mount to a ra/dec via the coordinate input page.  I believe a mod to the explorestars is coming to remedy this in which the point mode/track mode indicator will also become an active button by which a user can get the scope back into either mode by pressing.  

The reason a goto after centering does not put you back where you centered is because the goto location is not centered ... if it were you would not need to manually center the thing in the first place.

This behavior we are discussing above is not what the original post was about though as that problem had to do with lack of motion while guiding.  But I’m glad it came up because the point mode behavior of the mount can always use explaining.

You might ask why have the track mode if it won’t keep the scope pointing where I want it? Why go to the moon? Why does Rice play Texas? (JFK speech outlining his vision for going to the moon, happy anniversary Apollo 11). Track mode is a smooth sidereal tracking of an object optimized for a mechanically polar aligned scope.  This is what is needed for astrophotographers.  Point mode is at the microscopic level a step by step bumping along of the scope in ra and dec for use when the scope is not mechanically polar aligned but has had a 2 or 3 star alignment performed.  It is like a bird dog fixated on a target no matter what.  As the earth rotates the ra and dec mount axes must both move to keep the scope pointing to the correct celestial coordinates of an object.  Bird dog.  The microscopic bumps are not visible to the eye when one is doing visual observing and thus the mode is intended for that case.  The bumps happen 5 times a second.

Making the indicator an active toggle button is going to be a nice help for visual observers.  


Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired

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