Im with John on this one James, the right tools in the right hands will get it just about perfect, you cannot not be right when your looking at 3rd or 4th reflections eg correct me if im wrong the image has gone from your eye piece down the tube and back again 3 times now on my 1200FL F4.7 newt thats nearly 7 meters do some quick trig on that and you will find you are in the micron region of accuracy. I believe that auto collimators are readily able to get within 10 micron of optical alignment (assuming your reference spot and the like are right).
Pixel peeping can be hit and miss unless your seeing is BRILLIANT eg your stars are virtually still and even so can still hide optical collimation as if your seeing is better than 1 arc second (which it generally is not) then depending on your camera/FL set up your pixel is actually under the seeing limit! My F4.7 + qhy9 mono produces a 0.93 arc second per pixel so you see its kinda close ish. Then you have to contend with your mounts guiding/tracking and hopefully you are 100% guiding on a pin point if it wobbles your star has a whoopsy in it are you able to detect the difference in a guide error vs optical error from looking at a pixel?
I know its getting nit picky and all theoretical but at the end of the day if you take a image especially with newts you will see the ones who have nailed their collimation look at the diffraction spikes they generally have clearly seperated rainbows in them. I know that when i get my collimation right they are very distinct when i am out.... they are just whiteish.
Brendan
