Help please - telescope alignmnet - offset centre of rotation ?

[MikeODay]

I was playing about with trying to check/improve my polar alignment.  In the process I pointed my scope as close to the South Pole as I could get and then rotated the RA axis through almost 180deg.  I discovered that the centre of rotation of my telescope is offset from the centre of the image sensor.  (please see images below)

Telescope:  Skywatcher Quattro 10"

Camera: Nikon D5300 (6000 x 4000 pixels)

Rotation offset:. 708 pixels ~= 9.4' (or about 12% of the width of the sensor)

Please note that the collimation of the scope seems to otherwise be ok.

 

Questions I need help with please:

1. Is this in fact due to an offset centre of rotation (is this also known as the "optical centre")?

2. Is it a problem or can I just ignore it?

3. Can I do anything about it or is it a feature of the Newtonian design?

4. When I align my GOTO system should I centre the series of alignment stars at the image centre or at the centre of rotation or does it not matter?

 

Thanks very much for your help.

 

and a crop with annotations ...

 

[Carbon Brush]

The optical axis of a scope is not necessarily the same as the mechanical axis.

I once owned an Orion Optics UK scope that had the optics way off the tube axis. At about 20 metres, they were about 400mm apart apart. That was tested by viewing a target mark and projecting a red dot from a laser fastened onto the OTA.

My fix (from memory) was to adjust the primary mirror so the optical and mechanical centres were coincident, then go through the usual collimation.

Hope this helps.

[MikeODay]

5 hours ago, DavidValentine said:

The optical axis of a scope is not necessarily the same as the mechanical axis.

I once owned an Orion Optics UK scope that had the optics way off the tube axis. At about 20 metres, they were about 400mm apart apart. That was tested by viewing a target mark and projecting a red dot from a laser fastened onto the OTA.

My fix (from memory) was to adjust the primary mirror so the optical and mechanical centres were coincident, then go through the usual collimation.

Hope this helps.

Thanks David.

Does it matter if I leave it as it is?  Will it cause significant tracking or goto errors?

[MikeODay]

Does anyone else with a Skywatcher Quattro also have this offset?