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TWFS Alignment

CHARA-AO TWFS Documentation

Here we include notes, and links to documentation on how to use the AO system.

2015_06_11 - John's notes on aligning and using the system : JM's 2015_06_11 Alignment Notes

2015_12 – John wrote down the new procedure for aligning TWFS.

Following troubles of previous night, Mike, Judit, Laszlo, Matt, John all worked to align S1 WFS.
Here is a modified procedure: Use Red Laser and blank glass for dicroic
1. With no TWFS hardware in the way, adjust beacon to be centered in the acquisition hole and in center of the focus range. This is done using a cardboard target attached behind the TWFS. Mark optical axis center on the cardboard
2. Put in collimator. Focus and adjust to maintain the optical path by hitting the mark on the cardboard. Check that collimator is in middle of its range (+/-40000 counts).
3. Put on camera plate. Adjust the tilt using flat mirror (or use the mirror in the 1/2“ lens tube that comes with alignment kit).
4. Put paper target on back cam to find optical center (or use the target on front of 1/2” plug that plugs into the hole, that comes with alignment kit). Adjust WFS X,Y to center beam onto this target.
5. Put on lenslets. screw in telecentric relay (which should have been already focused)
6. Put on camera. Use range of motion allowed by the screws to center light at (45,45) on the detector. (see camera settings)
7. Spin lenslets. find the rotation axis. Try to move the rotation axis to the center of the pupil (secondary obstruction) as allowed by the loose screws that attach the lenslets.
8. Fine tune or do final correction by moving WFS x,y to lenslet rotation axis to the secondary obstruction. If this required a large move, then 'move back' the light to be centered at (45,45) by using the collimator.
9. adjust collimator focus (by hand) to fill the lenslets as expected. nominally 10.7 pixels between spots.
Looks much better now but not perfect.. could the collimator have been mounted backwards again? need to find out.

Note that it is tempting to use the collimator to align the spots on the camera. This is generally not a good idea… e.g. moving the collimator by 0.1mm will move the beam on the lenslets by about 0.1mm (0.3 lenslets equivalent), and will shift the image by about 0.3mm (one lenslet). But the beam will then shift on the first tele centric doublet lens by 0.73mm, which is close to the limit before vignetting (which is 1mm). To avoid vignetting, it is simplest to move the entire WFS assembly - the movement range is approximately +/- 3 lenslets prior to vignetting.

If the spots can't be moved far enough by moving the full WFS assembly… then the collimator should actually be moved so that the spots move in the opposite direction to that desired, following up by moving the WFS assembly. This is a last resort…

ao/twfs_alignment.txt · Last modified: 2018/07/08 15:06 by jones