[Kokatha man]

Hi leinid - the 3 screws on the back of the secondary mirror (the open end of tube) adjust the tilt of the secondary as well as hold it in the orientation I mentioned before (the bits about having it appearing centralized and concentric within the bottom of the focusser tube.)

The central bolt/screw (also at the back of secondary and having the aforementioned 3 screws around it) is a spring-loaded "toggle" bolt/screw that determines where the secondary is in relation to the bottom of the focusser tube: "tightening" it by screwing it clockwise moves/pulls the secondary away from the primary and towards the open end of the tube, and vice-versa.

This means that if you need to move the secondary away from the primary you must slacken off the other 3 screws: but in your case if, as it appears, you need to move the secondary towards the primary, you can just turn this central bolt/screw anticlockwise and the secondary will move down the tube towards the primary (by spring pressure.)

When you've got it central under the focusser tube you do the bit where you turn it (the sec mirror) by hand to make the sec appear circular/round within the focusser tube's outline and also concentric within the focusser tube. In answer to your question about the central bolt/screw and turning the sec mirror: if the 3 aforementioned screws are not pressing on the back of the mirror the mirror and holder can easily be turned/rotated by hand as the central bolt doesn't actually lock the assembly, it only holds it in the position you set it in under its own spring's tension. There is no tightening or untightening of the central bolt/screw as such - unless you go too far with turning it one way or the other, which is neither necessary nor likely in normal adjustings. After doing the above manoevre you then need to "lock" or "set/hold" the secondary assembly in this position by pinching up" the 3 screws to hold it so. After this is achieved you then "fiddle" with the 3 screws to get the "tilt" of the sec correct as per the instructions, before moving to the primary to adjust that. You will find that you need to go back and forth a few times between these last adjustings of sec and primary to get everything all concentrical.

Cheers, Darryl. ps - bob's knobs instead of the 3 phillips head screws make life so much easier here!