The British weather affords us few opportunities to image the night sky, so we don’t want to waste precious astrophotography time hunting and the sky for our targets. Once you have a permanent observatory, you need to make sure your telescope pointing is as accurate as possible.

There are a number of factors and tricks to bear in mind when trying to get your pointing as goods as possible for your equipment. Whilst it is possible to invest in software like Tpoint analysis to create a model of your mounts inaccuracies, this is perhaps beyond the means of most astrophotographers.

The first thing to remember is that the mechanics of your mount limit the accuracy of your pointing. The motors and optical encoders on your telescope mount could , in theory, point with sub-arc pixel accuracy. However, this doesn’t happen for a number of reasons.

First of all, polar alignment. All telescope pointing technology works best when the mount is well polar aligned. However, this is difficult to get perfect because the RA axis of the mount, the pier and everything else will sag a bit depending on where the weight of the OTA is positioned. All we can do is make sure the telescope mount is fixed to the ground as rigidly as possible, and make the polar alignment is as good as we can get it with drift alignment.

Drift alignment is the best approach because it does not rely on the optical axis having good alignment to the mount. Take time over the polar alignment for a observatory mount – if the mount isn’t going to move for a year, then spend a whole evening tweaking the polar alignment.

The telescope must also be rigidly fixed to the mount, and properly aligned as per your mounts instructions.

However, regardless of making everything as well aligned and rigid as possible, it is impossible to get it perfect. Because of this, most GOTO telescopes have a facility to synchronise the pointing model on a star near to your target, and then perform the final GOTO – this is known as High Precision mode or similar.

What a lot of observatory telescope mount users fail to appreciate, is that this local syncing process total removes the need to perform an inital alignment of the scope. When the scope is switched on in the home position, it can often slew accurately to a bright star without any setup aside from entering the time.

Here is my process with Meade Autostar:

  • The scope is position in the polar home position, with the scope “on top” of the mount and pointing north.
  • A webcam is fixed to the finderscope to save my neck and allow remote operation.
  • Turn the scope on and enter the date and time.
  • Connect the planetarium software (skymap) to the mount. Skymap now shows the mount as pointing at the celestial pole.
  • Use skymap to tell the mount to slew to a bright star not too far from the pole (e.g. vega).
  • The mount slews, and when it finishes, more often than not, Vega is visible in the webcam looking up the finderscope.
  • Previously the cross hairs of the finderscope have been aligned with the CCD camera looking up the main telescope. It is a simple operation to centre the bright star in middle of the CCD field of view.
  • Then I tell skymap to sync on Vega – it will update its pointing model.
  • Now I tell the scope to slew to a nearby target – e.g. M57 . The target will now be visible near the centre of the CCD field of view.

Very simple, and no wasted time doing “three star alignment runs” when all I want is one simple target on the CCD!