[Shiraz (Ray)]

Congrats Justin - really good to hear that you have had a successful outcome. Would it be worth trying to remove the residual 2mm by tweaking the secondary a tiny bit more - or is that close enough?
I agree with your assessment that this is a confirmation tool. Thanks very much for your help in sorting out just what this thing actually does. Regards Ray

I have been doing a bit of experimenting myself and conclude that, for conventional Newts:
1. this device is an adjunct to normal collimation tools - it will tell you how things are aligned and can indicate how to adjust the secondary (or possibly the focuser or primary if offset sideways), but the standard collimation procedures should always be used after any tweaking.
2. if you have a Newt with a central secondary, the light column will be tilted towards the focuser as a normal outcome of collimation. If you have a Newt with offset secondary, the light column should be central. In either case, don't mess with anything if the column of light does not run near any hardware in the input aperture or focuser extension (but remember that you need to allow half the diagonal of the CCD for clearance at the edge of the column).
3. if the light column offset is great enough to allow unwanted diffracting objects to intrude into the beam (easy to see), you can only adjust by moving the secondary and recollimating - you cannot fix anything by adjusting the angle of the primary in isolation.
4. If you are using a very fast Newt with a central secondary for imaging, it is worth considering a remake of the secondary holder to introduce some offset - turn it into an astrograph with a central light column.
5. and if you have gone to the massive trouble and expense of making one of these things, you may as well use it to accurately set your spider vanes as well.