Secondary Mirror Offset?

[ausastronomer (John Bambury)]

Originally Posted by Jason D

do NOT worry about how the secondary mirror is mounted.

Jason

Hi Jason,

While that is fine in theory; and in fact in practice, in terms of telescope performance, there are other things to consider. The main one being that most people that spend somewhere between $10,000 and $100,000 on a custom built truss dob don't understand the optical theory behind collimation and they don't look at collimation ray trace diagrams. They just expect everything to be squared, properly symmetrical and properly aligned and positioned. The fact that it doesn't matter in practice in terms of telescope performance, is totally academic to them. In this regard a well collimated laser does a good job of squaring the focuser and positioning the secondary when the Upper Cage Assembly is initially being set up for the first time.

Cheers,
John B

[Merlin66 (Ken)]

We seem to have drifted away from the needs of the original post and into the realms of multi thousand dollar telescopes.....

[Jason D (Jason)]

Originally Posted by ausastronomer

Hi Jason,

While that is fine in theory; and in fact in practice, in terms of telescope performance, there are other things to consider. The main one being that most people that spend somewhere between $10,000 and $100,000 on a custom built truss dob don't understand the optical theory behind collimation and they don't look at collimation ray trace diagrams. They just expect everything to be squared, properly symmetrical and properly aligned and positioned. The fact that it doesn't matter in practice in terms of telescope performance, is totally academic to them. In this regard a well collimated laser does a good job of squaring the focuser and positioning the secondary when the Upper Cage Assembly is initially being set up for the first time.

Cheers,
John B

John, it is the other way around. In my last post, I was advocating for a simple and a practical collimation method.
A laser does do a good job is squaring the focuser but it does not do a good job in positioning the secondary mirror under the focuser -- unless it has a holographic attachment.
Jason

[ausastronomer (John Bambury)]

Hi Jason,

You don't use the laser and center spotted secondary for anything other than the vertical positioning of the secondary holder in the UCA; and it does an excellent job of this task. You don't use the laser or center spot for any of the other secondary adjustments like tilt, or axial rotation.

Cheers,
John B