Does Go-To Dob Mount need to be level to accurately track?

[Scoobyroo]

Hi all.  Think this may be a silly question, but I can't seem to find a definitive answer.

I have a Sky-Watcher Heritage 150P Virtuoso GTi, with Go-To dobsonian table top mount.  I typically use the scope on my garden table, which is super sturdy and works well.  I would like to take the scope to a darker sky area not far from where I live and am considering placing the scope either on the car bonnet, or directly on the ground (on a waterproof blanket).  Pro's and cons to each of course (comfort, etc), but my question is more related to if (how well) the Go-To tracking system might work?

Normally, the base is Go-To calibrated on a level surface, north aligned and then uses two stars to finalise the calibration (with manual adjustments as necessary).  What happens in a scenario where the surface is not level?  In theory, the the 'two-star' part of the calibration should consider any 'wonkiness' of the surface the scope is mounted on - but everything I'm reading states that the tabletop mount must be level.

Anyone have any experience with this?

(wasn't sure if I should be posting this in 'mounts' or 'software' - mounts seemed the best fit).

Txs.  Rick

[happy-kat]

if the mount is not level and say you aligned using stars in the east and swest then went to an object in the nw then I guess you wouldn't see it in the eyepiece

[lvan]

I use levelling feet which also adds a bit of height. Take a small stool and you’re good to go.

 

 

 

[GordonD]

My Dob does seem to benefit in terms of Go To accuracy by having the base board level.  I say seem, as even when levelled it can be hopelessly unreliable some times, and work well at others. I have not figured out why. I think the bearings and motors are not really up to the job - this is the SW 12". 
But since I started making sure it was as level as I could make it, it has at least improved. I use a circular bubble level. 

The thing is I don't know why that should be.  In my head, if you have done a 2 star, or certainly with a three star, alignment I always think that should be enough information combined with an accurate location and time for the computer to work everything out that it needs, level or not. But level it seems to need, anyway.

Not sure of that helps.

[Mandy D]

Having it not level in the north-south direction is going to be equivalent to a change in latitude, so should not present a problem. Extrapolating this idea suggests to me that it won't matter east-west either, but I have not really thought that through yet.

[Rossco72]

I know my 14" goto Dob performs best from a levelled base. I added levelling feet and a bubble level to aid with this. I also have some magnetic weights to help balance if I am using heavy eyepieces or cameras etc.

I don't know the science behind why it should matter, but practice tells me it does so i do it.

[Scoobyroo]

Thanks all for the responses

I managed to grab a few hours with the scope again on Saturday (break in the clouds), but had to move the table it sits on (which is super sturdy) to a different area of the garden to get a good view of the moon in the slot I had.  The ground here is most definitely less level then where I normally spot from and I did notice that my Go-To was even less accurate than it normally is.  As such, I definitely feel that levelling is having a beneficial impact, regardless of calibration.

My Heritage Virtuoso 150P has a bubble level (though it's very inconveniently place right in the centre of the base plate, where it's difficult to see when the tube is on 😆).  I was hoping I may find the legs adjustable also (thanks for the tip Ivan), but seems they are fixed.  I'll take a look around to see if I can find adjustable replacements 👍

Thanks again all... R

[StevieDvd]

OK let's go through this with some logic (as I hope the scope does).

If it were perfectly level the mount would need to find which way it was pointing to work out its position compared to North.  Then it can turn round (360 degree) flat disc and elevate the scope to the target (it turns & elevates at the same time).  To track it would make small adjustments to both Alt & Az to keep it aligned.

Now if your flat disc is not level, let's say West/East, but level North/South then choosing alignment stars in West & East would allow it to compensate. But if you used stars in North/South it would not compensate for the  East/West slant.

In practice you'd be hard pressed to hit that exact situation, so selecting a couple of alignment stars should get the compensation figures worked out  - but they won't be as good as what you'd get with a levelled mount.