I had to go back to the beginning of this discussion to make sense of the tangents.
...Many beginners purchase a laser collimator and follow the proper steps to find out they canâ€™t see all of the primary mirror clips via the secondary mirror. By proper steps I meant aligning the secondary mirror by redirecting the laser beam to the primary center then aligning the primary mirror by redirecting the laser beam back to its source. When beginners run into this issue they wonder if the problem is with the quality of their laser collimators. Then they realign the secondary mirror using the collimation cap to bring all of the primary clips to view. Now the laser beam no longer hits the primary mirror center. At this point frustration builds and no matter what they do, they just canâ€™t reconcile between the collimation cap and the laser collimator.
From this opening salvo I think I now see your vision process.
The goal is to achieve good axial alignment, with the primary mirror reflection more or less centered in the secondary mirror, using a simple thin beam laser and a collimation cap. We'll assume the tools have been checked and are up to the task.
The solution is a systematic approach, delegating focuser axial alignment (secondary mirror tilt) to the laser and secondary mirror placement (rotation and fore and aft movement) to the collimation cap, repeating the two alignments until both are correct. The alignment signatures are the laser beam aligned to the primary mirror center spot (focuser axis) and the primary mirror reflection "centered" in the secondary mirror (secondary mirror placement).
(Final primary mirror alignment I presume will be achieved with the collimation cap.)
Your procedure should resolve (to the limits of the mechanicals) the axial alignments and the secondary mirror placement. You start to address the mechanical alignment issues by including spider adjustments (at the OTA attachments)--but then you stop there (?). If your goal is "close enough", which I think is quite acceptable, I'd leave the spider centered and go with assuming the mechanicals are OK.
But, because the focuser/spider/secondary mirror geometry is basically unknown--there's a good possibility that the user will find himself in an infinite loop attempting to resolve a secondary mirror placement error that can't be resolved because of mechanical issues. This usually plays out something like, either the secondary mirror looks round but the primary mirror reflection isn't centered, or the primary mirror reflection is centered but the secondary mirror looks elliptical, or some variation in between... At this point, the user needs to choose "close enough", or a closer look at the mechanicals (possibly beyond the expertise of a beginner).
And I'm OK with using the "window" analogy (it's synonymous with using the bottom edge of the sight tube--except the window doesn't move with a sight tube--but we'll assume a sight tube is unavailable) for assessing which "direction" the secondary mirror needs to move. But if the secondary mirror isn't already close to where it belongs, the procedure could take many
iterations and leave the beginner second guessing how much correction is actually needed (many "tiny" adjustments or one "big one"
) and ultimately relying on "hit or miss".
In this sense, starting with the focuser axial alignment and a secondary mirror which could already have a significant tilt/rotation/offset alignment error, or a rudimentary secondary mirror "centering" under the focuser followed by a focuser axial alignment, should have little impact on the beginner's successful resolution of the alignment errors.
I guess what I've been trying to say, is that even with a systematic approach to resolving the alignment errors, even with
a sight tube, there's plenty of complexity here to confound the beginner who doesn't fully understand the mechanical geometries and the limitations they impose on the secondary mirror placement.