You do realize that you just called Vic Menard and Nils Olof Carlin secondary alignment ideas irrelevant!!!!

Gosh, am I supposed to start trembing, or what We are not discussing names here, are we. Frankly, names do not matter, yours and mine included.

Vla

No, I did not expect you to â€œtrembleâ€ but I did expect you to show more "respect" to collimation ideas presented by Vic Menard and Nils Olof Carlin. After all, both have significantly contributed to improving and clarifying collimation and both are well-acknowledged collimation experts among the amateur astronomers.

FYI: The (D-A)A/4S formula is not exact but a highly accurate approximation. The mathematically accurate formula is long and involves the solution of a quadratic formula. For D=300, S=1250, A=70, the exact offset is 3.228337732mm, the exact H' is 376.2239073mm, the F'-ratio for the extended apex cone is 5.420746358. The (D-A)A/4S formula gives 3.22mm. Of course, pursuing offset precision beyond 0.1mm would be absurd; therefore, the (D-A)A/4S formula is more than adequate.

Well, thank you, Jason - I appreciate you acknowledging something posted by me as valid and useful. You seem to have missed it, but I did state that the above expression for BO shift is not absolutely accurate, since it neglects mirror sagitta. When it is taken into account, the formula is only a bit more complicated: BO=(D-A)A/4[S-(D/16F)].

Vla

Do not be too presumptuous!!!! Sagitta has nothing to do with the point I was making. My point is that (D-A)A/4S is not an exact formula â€“ mathematically speaking â€“ for calcuating the offset for a line segment slicing an isosceles triangle at 45 degree angle.

In addition, despite your claim that you have independently derived the above formula (D-A)A/4S, you do not seem to be aware that the formula assumes the eye is placed at the extended apex point â€“ not at the focal point.

For several pages in this thread we were debating the optimal placement of the eye to center the illumination field. You kept insisting that the eye has to be placed at the focal point to center the illumination field. You did not even have a concept of the extended apex point. Are you agreeing with us now? That is, are you agreeing that the optimal eye placement to center the illumination field is the extended apex point?Let's see. What you are proposing is to place sight tube's pupil at the apex levelâ€¦â€¦. What do you gain by doing collimation in this manner? The field of full illumination gets centered around focuser's axis, as opposed to being 1.7mm decentered if you collimate from the focal plane level.

What about the other subject that consumed countless number of posts? I am referring to your incorrect formula:

UO/BO OFFSET = AS/(D-A)Hâ€™

Do still believe the formula is accurate?

Jason