Setting up the focus Positioning Slit assembly

Camera

Mark the position for the camera in reflection mode using the template brought from RGOC. Insert an alignment post in the hole in the optical bench 1.5mm away from the pivot point (i.e. 325mm from X). One further hole in the optical table should be on the line joining R to the pole of the camera corrector.

To mark up for transmission mode, firstly position a laser pointing from the transmission position, through the pivot point, and onto the centre of R . (If you remove the two collimators, and remove the dummy grating from its cell, this beam should hit the centre of R , and then go back through the pivot point.) This defines the optical axis into the camera in reverse. position targets on this axis, remove R and send a laser back along this track from the position of R . make sure the laser is firmly fixed to the optical table. Position the transmission mode baseplate on the bench using the template brought out from RGOC.

Position the camera on its in reflection mode baseplate, and measure the separation between R and the camera. This should be 1257.9mm. Note that the camera should be evacuated to get this measurement correct - the corrector moves inwards by 0.5mm when it is under vacuum.

To square on the camera to the optical axis use the slit axis laser - rotate the dummy mirror in the grating cell to direct the beam to the centre of R . This should then pass through the alignment post positioned on the line joining R to the camera corrector, and pass  1.5mm from the post close to the pivot point. It may be necessary to tweak the alignment of R to attain this. Insert a perforated target between R and the camera. Assuming the camera has been aligned off-line (it should have been) the only alignment required now is to square on the complete camera assembly to the optical axis defind by the slit laser. This requires some judicious nudging - the complete camera weighs of order 125 kilos, and adjustment of the kinematic adjustment screws. After squaring on, check the R to corrector spacing. Clamp the baseplate securely to the optical bench, and lock the adjusting screws on the kinematic mounts.

To position the camera for transmission mode, raise the camera from the reflection mode baseplate (using the documented procedure - see section ??), and position it on the transmission mode baseplate. Place a target on the laser beam coming from R and square the camera on to it by nudging the complete assembly. Do not adjust the kinematic adjustment screws - it should be possible to achieve alignment without doing this, and if it isn't then something is wrong!. Check the spacing R to the camera corrector - again, it should be 1257.9mm. Clamp the baseplate securely to the optical bench.

Setting up the focus Positioning Slit assembly