Hey guys,
Have a question concerning polar alignment. i know we can do drift alignment in the field cos the stars at zenith and at the horizons can be used. BUT what about if i'm doing ob from my balcony and i want polar alignent good enff to do some astrophotography work. With such a limited view of the southwest, how can i get a good polar alignment??
Thanks
Colin
polar alignment
Here's my take.
If you can only view to the SW and I am guessing you can't see the zenith, so you're seeing more about 15deg above the horizon, then probably the up/down alignment is more critical.
If you have a reticle eyepiece, then you should use that, centre a star near the horizon, align an axis of the reticle to your RA axis, then check for drift. If the star drifts North, then adjust your mount up, and vice versa.
After you've got the up/down sort of aligned, and alignment is still not good enough, you could work on your east/west alignment. Then you could try using as high a star as you can. If the star drifts North, adjust your mount West and vice versa.
After you get this, you might want to redo the up/down alignment as it may have been affected. Repeat as often as you need or until you give up :-D You have an advantage though. Once you do get it aligned, and you need to pack up your rig, don't move your up/down or east/west adjustment screws, and mark your tripod leg positions. You should be able to get it close to aligned again by just replacing the whole rig on the markings.
The important thing is to know whether the drift that you're seeing is northwards or southwards. The simplest way to confirm would be to move the whole telescope, firstly by looking into the eyepiece, to get the star to exit the eyepiece on the OTHER side of the drift direction, look up, and continue moving the scope. The direction you're moving the scope should be the direction of drift. Oh, point to note also is that the north/south mentioned above is not the magnetic north/south, but it's according to the celestial coordinates (e.g. if you're pointing towards the south horizon, then a northward drift is vertically up).
Hope this helps. Just trying to figure this out theoretically, so let me know if it works ;-)
If you can only view to the SW and I am guessing you can't see the zenith, so you're seeing more about 15deg above the horizon, then probably the up/down alignment is more critical.
If you have a reticle eyepiece, then you should use that, centre a star near the horizon, align an axis of the reticle to your RA axis, then check for drift. If the star drifts North, then adjust your mount up, and vice versa.
After you've got the up/down sort of aligned, and alignment is still not good enough, you could work on your east/west alignment. Then you could try using as high a star as you can. If the star drifts North, adjust your mount West and vice versa.
After you get this, you might want to redo the up/down alignment as it may have been affected. Repeat as often as you need or until you give up :-D You have an advantage though. Once you do get it aligned, and you need to pack up your rig, don't move your up/down or east/west adjustment screws, and mark your tripod leg positions. You should be able to get it close to aligned again by just replacing the whole rig on the markings.
The important thing is to know whether the drift that you're seeing is northwards or southwards. The simplest way to confirm would be to move the whole telescope, firstly by looking into the eyepiece, to get the star to exit the eyepiece on the OTHER side of the drift direction, look up, and continue moving the scope. The direction you're moving the scope should be the direction of drift. Oh, point to note also is that the north/south mentioned above is not the magnetic north/south, but it's according to the celestial coordinates (e.g. if you're pointing towards the south horizon, then a northward drift is vertically up).
Hope this helps. Just trying to figure this out theoretically, so let me know if it works ;-)
Celestron 9.25SGT, Meade ETX125, Orion ED80
This site has a video simulation and explanation on drift alignment, very useful: http://www.andysshotglass.com/DriftAlignment.html
