Re: [ATM] Mirror cell for an 8" mirror

["Jerry" <wa4guu@verizon.net>]

Olivier

If you mount the cell with traditional 120 degree collimation points in a
proper orientation with the focuser it is as easy to adjust as the 90 degree
configuration. Mount the cell with one of the adjustments in line with the
focuser and call the focuser side of the tube "up". That one will be the
"tilt up/tilt down" adjustment. Either one of the other two can be the tilt
left/tilt right adjustment. It doesn't matter that it will have some up down
component to its motion. Just ignore it. You adjust it to bring adjustment
onto the up/down tilt line and that one has no left or right component in
it's adjustment. The third point is used for longitudinal adjustment along
the length of the tube to bring the focus to the proper height at the
drawtube. Don't use that one for left right tilt. 

Collimation is a 2 or 5 step process. The first time is usually 5 steps.
After that if you don't use the longitudinal screw to adjust left right
tilt, 2 will be all that is necessary unless you have made changes up at the
diagonal and focuser.

Assuming the focuser and secondary are properly aligned, the sequence for
the primary alignment would be to:

1) Adjust the tilt left/right screw to bring the reflections of the center
of the focuser and diagonal onto the up down line. That is the line of the
axis of the focuser extended across the tube.

2) Then adjust the up/down tilt to center the reflections. 

It is collimated. 
If the focal plane is not at the desired height:

3) Adjust the longitudinal screw by the desired amount to correct the height
deviation at the focuser.

4) Adjust the left right tilt screw as in number 1.

5) Adjust the up down as in number 2.

Collimation complete.

The procedure for the 90 degree arrangement is the same as for the 120
degree arrangement. The 120 is just as easy as the 90 to adjust. 

Mechanically I think the 120 is best.

Jerry




-----Original Message-----
From: Olivier Biot
When doing so, you can
*decide* where to put the collimation bolts on the frame that supports
the cell. If you want, arranging the collimation bolts can then be
very easily done in a 90 degree configuration (as opposed to the more
traditional 120 degree configuration in symmetrical cells that reduce
to 3 points). Think of the collimation bolt in the right angle of this
setup as a pivot point or a joint that you normally do not need to
touch (unless you want to move the primary up/down along the optical
axis).


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