Obtaining an accurate polar alignment

This is one of those tasks that only needs to be done once if you have a permanent setup apart from occasional tweaking or if you change equipment on the mount, if you have a portable setup it has to be done every time the equipment is set up. If however, like me, you are able to leave the equipment set up under weather proof covers then it is not essential to do it every night.

Unfortunately this can be a time consuming job (anything up to an hour or so) but getting an accurate polar alignment is essential for long exposure imaging otherwise the dreaded field rotation rears its ugly head.

There are various methods of getting an accurate polar alignment including drift aligning and other techniques which can be found on the internet by looking in google so I won't be describing these in detail. However I will describe the process that I use as I use The Sky 6 software to control the Paramount ME and a very sueful program called T-point is included which is a mapping program to increase the accuracy of pointing which at the same time gives information as to the polar alignment and what adjustments to make.

First of all the Sky 6 software is started and then the mount is switched on (by this time all equipment is switched on and connected to the computer), then a link is made between the mount and the Sky 6. The first thing the software does is instruct you to 'home the mount' by which the mount is moved to a fixed position so that it knows where it is and what all the slew limits are, this is done by clicking 'ok' in the homing dialogue box.

Once the mount is homed, using the Sky 6 software I slew the telescope to a star close to home position and using the manual alt/az adjusters on the mount iteself I centre the star in the cross hairs of the eye piece on the telescope. When I have done this I will change the eyepice over to the autoguiding camera, focus it using Maxim DL and set it to 1 second exposures/continuous in focus mode which will give me a continuous update on the computer screen on where the telescope is pointing, I use the cross hair facility in Maxim to make sure the star is properly centred making any adjustment at the mount as necessary. In The Sky 6 software I now click on 'synchronise' so now the mount is polar aligned. This would be sufficient for observing but for imaging something more accurate is needed.

I will now open a T-point model and click on 'map' and then slew to another star nearby, this time using the telescope joystick (not the manual adjusters) I move the mount until the star is on the centre of the cross hairs of the camera image, then I click 'map' again. I will then repeat this process for about 15 stars. What this does is teach the mount the corections I make for each star and then it starts to make its own corrections and the pointing becomes more accurate. At the end of the '15 star mapping run' I open the T-point model and it tells me how far I am away from the celestial pole and what adjustments to make to the manual alt/az adjusters on the mount. I do this end then delete the T-point model and then open a new one, then slew to a nearby star and adjust using the joystick (from now on the alt/az adjusters are only used when instructed by T-point) and then click 'synch' as before and repeat the process of the 15 star mapping run. I may have to do this process 4 or 5 times which will take about an hour but by the end of it I will be within about 5 to 10 arc seconds from the celestial pole which is accurate enough for exposures in excess of 40 minutes+

This whole process sounds complicated but the software is very intuitive and it is very easy to do