Levelling a mount

[robhatherton]

I'm having some success using setting circles on my cg4 mount with my omni xlt 120 refractor. By 'some success' I mean they get me in roughly the right place a lot of the time.

If I've done a reasonable polar alignment how important is levelling the mount? I observe on my back garden lawn which is a bit uneven and the built in spirit level on the mount seems fairly crude.

Rob

[Stu]

If you are polar aligned then whether the tripod is level makes no difference at all. All it really does is get you closer to PA in the first place, and make sure there is no interaction between Alt and Az adjustments when getting to polar alignment.

Stu

[baggywrinkle]

If you want to have a level meter and have an iPhone check out ScopeTools.

I have always levelled my mounts be they AZ or EQ. Anything to take out potential tracking errors.

There are articles about the Celestron AZ mounts which say it does not make a difference being level or not. and same with EQ mounts. I cannot understand that, if your base line is out then errors must be added to the overall setting.  Someone please correct me if I am wrong..

[brantuk]

I agree with Stu. The only reason the manuals tell you to level the mount is so you can set your latitude using the altitude scale making it more straight forward to polar align. For the same reason it tells you to point the scope north - so you get a reasonable start at PA from a "close by" azimuth bearing. It's good practise I guess - but not essential - so long as you're polar aligned accurately it doesn't matter what orientation the tripod is at - could be hanging off the ceiling lol.

(If using setting circles on an alt/az mount however - to be accurate at all it's essential the mount is level)

[philj]

This old question just keeps coming around. Your mount has altitude and azimuth adjustments, e.g. its just like a big universal joint with which you can point your polar axis anywhere you want. So religiously levelling your tripod just means you wont have to adjust so much to get polar alignment. As Kim says, more convenient.

The tripod therefore can be at 45 degrees from horizontal if you wanted but you could still get polar alignment by adjusting the altitude and azimuth knobs and it wouldnt make a figs difference to the mount its just that it would be a faff to adjust it.

[m37]

Mind you, if you start from level and the altitude is set once it should be pretty close next time. Your mount might sink a bit in the lawn though so I wouldn't sweat it. I like to level my tripod first as it only takes a couple of minutes, but I'm all about the detail, sometimes too much if I'm honest...

[robhatherton]

Thank you all, particularly Stu and Brantuk. That's immensely helpful and what I intuitively thought. Makes life easier too!

Rob