[g__day (Matthew)]

Last week I pointed out how a German equatorial mount can be polar aligned beautifully even if the mount itself is far from level. This is a consequence of it having two axes of freedom that needed to be pointed to a precise spot in the sky. Once you have this aligned, clever software can get the pointing right – even if the mount is not level.

But there was one point I didn’t think off – does the software build an internal understanding of whether the mount is level or not and retain it when the scope is switched off or put into hibernate mode.

This is obviously mostly relevant to folk with permanent piers – but all users of goto mounts can be affected.

Basically if your mount isn’t level – but is SCP aligned – this situation can be adjusted for in the software – and most likely is accommodated for by most mounts / hand controller combinations.

But what happens if you put your mount into park / suspend mode and re-wake it? Specifically does the mount keep not only the alignment data (e.g. 3 widely spaced stars) – but also the levelling data?

In the case of a Vixen Atlux with a SkySensor2000-PC hand controller – I suspect not. That is I have aligned my mount reasonably well on its pier – I’d say it’s within an arc minute of the SCP on both axes. But I’m beginning to suspect my mount is somewhere between ½ a degree to 2-3 degrees off level. Why – because on power on resume – my pointing is always about 30 arc minutes of its three reference stars in the same direction (mostly RA but also DEC) each day.

Once I re-align on these three stars pointing and tracking is very, very, very good. But on initial power-on resume from the previous nights viewing - all objects are consistently ½ a degree out of position.

Pondering why this could be (on the relevant Yahoo group) lead to the intuition that the level of the mount plays a key part – and this mount level or not information isn’t preserved between power–on – so the mount simply assumes a polar aligned mount is also a level mount!

Has anyone else experienced this type of behaviour? Appreciate your thoughts.