[Shiraz (Ray)]

Hi Adam,
The primary mirror in Justin's scope is definitely tilted a bit, but it has almost certainly ended up that way as a normal outcome of the collimation process. The gadget can only show you this sort of issue, but it cannot indicate directly what the cause is (unless it is being used to identify intruding diffraction sources). However, it does give you some idea of what components to try adjusting if you identify that there is a problem (see below). I am not sure how generally useful this is going to be as a tool for Newt owners - anyone with a Newt above about f4.5 will be wondering why bother, since their systems tolerate typical alignment errors - its possibly only the owners of really fast Newts (or ones with rotating heads) who will see it as useful. Whatever, it certainly helped me to quickly understand what was going on with my own f4 scope.

Justin. If the scope is collimated, the collimation process will have aligned the primary so that it's optical axis meets the focuser axis on the surface of the secondary (and hopefully somewhere near the centre of the secondary). If the secondary is in roughly the right longitudinal position, the column of light coming out of the OTA should be symmetrical about the primary's axis (provided the LED is on the focuser axis - rotate it to check that the column does not move too much). As an aside, the LED acts as a nearly point source and it will not matter much where it is pointing, as long as it is positioned near the centre of the focuser aperture and generally aimed towards the secondary - it shares this insensitivity to pointing with the Barlowed laser.

It should be possible to walk the axis of the primary across to the axis of rotation of the head by adjusting the spider to move the secondary and then recollimating after each move - when the light column is centred after a move/collimate, the optical axis should also be centred (note that the secondary shadow should be offset a bit away from the centre of the column at this point). Provided none of the mechanical components are grossly out of square, this should be all that is necessary to get the optical axis and the axis of head rotation to coincide. At least I think this is the case...I am having some difficulty getting my head around the complications of a scope with rotating upper section! Will be very interesting to see what you come up with.

Regards Ray