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Projecting the concentric ring pattern on a surface in front of the scope is the last step in the laser collimation procedure. It is for adjusting the angle of the primary mirror. It will only work if all the previous alignments of the focuser and secondary mirror have been made correctly.
The only thing to look for here is concentricity of the circle projection with the secondary shadow. You can make the gap between the secondary shadow and the first ring visible outside it even all around. Actually, you are seeing the secondary baffle shadow, so the baffle must be concentric with the secondary as well. The size of the projected rings can be adjusted to make the gap narrow by racking the focuser.
> . . my concern as being the spacing between the light rings,
> which can be clearly seen to be different left to right -
I'm not sure I understand this. The uniformity of spacing between the rings is not affected by collimation adjustments, and is given by the rules of diffraction. The picture was taken at an angle to the screen, so everything, including the circles, is foreshortened left to right, and taller up and down. The concentricity may be a tiny bit off, but it's close.
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