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Don't get me wrong, I really like my autocollimator thingie and I'm not saying you don't need one - you do. But we are not replacing it with an eyepiece here - it's being replaced with a camera. Lucky for me, my Catseye has two holes, so I can also view the alignment off centre and this helps a lot. But remember the sensor might not be square, the weight alone is probably enough to push the scope out of collimation - as per the video on my website.
It's also a practical matter - for the same reason lots of people use the CCD to do the polar alignment rather than swap the camera out with a reticle and then swap back to the camera, it also sometimes easier to use the CCD to do the the final collimation. Removing the camera to insert the autocollimator and getting it back in the perfect position is not always easy.
I'm not talking about the endless theory of collimation here which we all know back-to-front and no-one can despute that. It's the practical side that we all have to come to grips with and find a way that works for our own setup. For me, its easiest to use the CCD Sensor as the reference plane, and work back from that.
Lets say you collimate with a catseye and get it all perfectly stacked. Then you take an image and notice that the stars are wonky on the right hand side only. What do you do? Put the catseye back in and start over? Maybe. The alternative it to center a star and push it left or right using the collimation adjustments and see if it fixes it. That's what I would do.
James
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