Home position on mounts.

[JIm19130]

I too am a little confused with the answers here.   Some say you don't need a marked home position.   This sounds inaccurate to me.  

I have a Skywatcher EQ6-R Mount.   When I Polar Align, I set the mount toward Polaris, approximating the altitude of Polaris on the altitude dial.  I also try to approximate the azimuth so when I start looking through the polar scope to align, Polaris can be located fairly quickly. 

Next, I have come to learn that I need to slightly rotate the RA axis so that the  illuminated reticle circle (I had to adjust the illumination down to 4% with the GoTo utility control) with crosshairs is vertical with the mount.   I've been told I should use the GOTo controls to move the RA axis.   I adjust the RA axis so I can duplicate the position of Polaris on the circle with what I will see in the Polar Align display, since in the display the crosshairs are positioned like a + (vertical and a horizontal line that matches the horizon).  I ignore the 0,3,6 and 9 on the crosshairs  

Then, using the altitude and azimuth control knobs, and looking through the polar scope, I carefully position Polaris precisely in HH:MM position that I see in the App around the circle that I see inside the polar scope.   I then return the RA axis to the "home position" using the hand controller.  

This is why I don't understand why some people say home position is irrelevant for both the Dec axis (which is at right angle so I can see through the polar scope) and the RA axis.  If I didn't return the axes to the home position, the mount's GoTo wouldn't be starting in the correct position.  

(By the way, I have noticed that when I first initialize the GoTo and input the long/latitude, time zone, date, time, etc, the GoTo calculates an "Hour Angle" and the figure given does not match the HA figure given in the Polar Align App.  I don't know why this is the case, but I use the HA given in the app.   It would seem to me that they should match, but they don't.)

 

Has anyone else noticed that the figure given for HA by the Skywatcher GoTo doesn't match the HA figure given by the Polar Align App??

 

  

 

[Robindonne]

Ha great! One more questioning user!   But in the beginning, (and before polaralignment could be done with main or guidescope) its not really important what direction the scope is aimed for a good polaralignment.  
just Polaralign with the polarscope and thats it.  The position of the mainscope will be determined after you’ve done the 3 star alignment Or platesolving.  
 

 I asked this “home position” question because a lot of modern systems have the ability to polaralign with one of the cameras (main/guide).

And thats when a marked homeposition could be very handy.   
 

the traditional polarscope needs to be calibrated in the mount, as perfect as possible. But when doing a modern polaralignment through one of the scopes, suddenly you’ve lost your calibrated “eye” for this polaralignment.   Strange!!

I have to mention that that modern polaralignment can only be done accurate after the cameras have taken some shots from multiple positions    That way the software can calculate the current angle/position of the mount

at this moment i have some diy waterproof fineliner marks on my scope to help me start in homeposition.  
 

the differences you mentioned in the real position of polaris and the given position shown in the “PS align pro” app, Are because a bug in the app i think.  I have the same issue and noticed the timezone in the ps align pro is different then how it should be.  For example in Holland +1 and the app shows +2.  When i change the timezone in my synscan app to the faulty timezone in the ps align pro app, suddenly they both show corresponding figures.  So its a bug i assume
 

 

Edited June 30, 2020 by Robindonne