How does EQ goto mount alignment work?

[johngwheeler (John)]

I've just bought a Celestron AVX goto mount, but don't yet have a telescope, so haven't been able to try it out fully. I have some basic questions about how the setup and alignment process works.

1) If the mount is only very roughly polar-aligned (i.e. just setting latitude scale and moving tripod to point roughly to pole - South in my case), what function does the "one star" or "two star" alignment have if it doesn't physically change the mount position?

It seems to me that this may allow the mount to become aware of it's orientation, and maybe calibrate its go-to ability, but wouldn't fundamentally allow it to track objects because the polar alignment is not accurate. Does the mount do some adjustment to compensate for poor tracking by using both RA and Dec motors, in the way that I imagine Alt-Az go-to mounts work (which I assume must use both motors as they are not polar aligned at all)?

2) it makes sense that the mount must be physically aligned to the celestial pole by moving its altitude and azimuth settings, but the manual is pretty bad in explaining this. I gather that the physical alignment can be done by centring a known star multiple times and offsetting drift according to direction prompts on the hand controller. When the drift is zero over time, then the mount is correctly aligned. Is this how it works?

I haven't been able to experiment with the above without a scope, so any clarification you could give would save me time when I actually get the scope!

Thanks and best regards,

John.

[raymo]

You have to do a one or two star alignment a few times to get the
Go To working properly.[ It becomes quite easy and quick with practise ]. You have to adjust the mount's altitude and/or azimuth setting between each alignment routine.
If you are only doing visual, just setting the altitude correctly, and
aligning the mount due south [NOT magnetic south] with a compass
will allow quite good tracking. You only need accurate polar alignment for
long exposure photography.
The mount will not compensate for poor alignment by using both motors.
It cannot do that because of a thing called field rotation. To track
accurately, an EQ mount has to be very well polar aligned so that only occasional nudges are needed in Declination. An alt/az mount does not
allow long exposure imaging due to the aforementioned field rotation
that it suffers from. Your last point refers to a polar alignment routine,
which is different to a star alignment. The star alignment is performed
so the scope knows where it is in the sky. Confused? There are many
tutorials on the subject in Youtube.
raymo

[Somnium (Aidan)]

Originally Posted by johngwheeler

I've just bought a Celestron AVX goto mount, but don't yet have a telescope, so haven't been able to try it out fully. I have some basic questions about how the setup and alignment process works.

1) If the mount is only very roughly polar-aligned (i.e. just setting latitude scale and moving tripod to point roughly to pole - South in my case), what function does the "one star" or "two star" alignment have if it doesn't physically change the mount position?

It seems to me that this may allow the mount to become aware of it's orientation, and maybe calibrate its go-to ability, but wouldn't fundamentally allow it to track objects because the polar alignment is not accurate. Does the mount do some adjustment to compensate for poor tracking by using both RA and Dec motors, in the way that I imagine Alt-Az go-to mounts work (which I assume must use both motors as they are not polar aligned at all)?

2) it makes sense that the mount must be physically aligned to the celestial pole by moving its altitude and azimuth settings, but the manual is pretty bad in explaining this. I gather that the physical alignment can be done by centring a known star multiple times and offsetting drift according to direction prompts on the hand controller. When the drift is zero over time, then the mount is correctly aligned. Is this how it works?

I haven't been able to experiment with the above without a scope, so any clarification you could give would save me time when I actually get the scope!

Thanks and best regards,

John.

There are 2 alignments for a goto mount, 1) its polar alignment and 2) its orientation to the current sky. the second is served by the go to alignment process but if you are not polar aligned then the mount will not correct for any field drifting (unless you have a guide camera). also, if you are not properly polar aligned and you do a 1 or 2 star alignment on your hand controller, you are likely to find that your pointing accuracy will be way off making it difficult to find objects. even if you are only using the scope visually, the night will be a whole lot more fun and less painful if you align to the SCP. most common method in the southern hemisphere is using drift alignment (youtube a tutorial). there are also tools like astrotortilla that can help you to really dial in the alignment, but that is really for extremely long exposure photography.

[raymo]

I imagine that your Celestron mount has a polar alignment routine built
into it like my HEQ5 does.
raymo