Quote:
Originally Posted by erick
OK, I'll keep "shooting from the hip" all the time then 
But I cannot visualise it, Gary. Isn't it the curved surface of the EQ table that moves in RA? How does the Azi movement of the dob become an RA movement? If I move the scope in Azi on a table, the OTA pointing direction surely doesn't move in the RA direction? 
See attached, thanks to:- http://www.backyardvoyager.com/EQplatform.html
Perhaps we'd better go to another thread - "Equatorial tables for Dummies"?  |
Hi Eric,
You're faster on the draw than me.
I was still editing my original post when you
provided your follow-up and I was in the process of correcting where I typed that
Az becomes RA and Alt becomes Dec. The key to appreciating what happens
when a Alt/Az mount is placed on a platform is that a new third axis is introduced which
is a polar axis. If I don't spot one online, I will try and create a graphic to help
demonstrate it, as it is not obvious to many upon initial inspection the first time.
The good news though is that when a Dob is mounted on an equatorial platform,
the third polar axis transforms it into an equatorial mount. Once the platform is
polar aligned and assuming the platform is tracking, any arbitrary point in the
sky to which the scope points will then remain within the FOV.
Best Regards
Gary