Aluminisation

M1 M2 realuminisation. *Among the "normal" work together with the students and the astronomers, we gave a thorough clean of the telescope structure and the dome.

*Reflectivity: The M1 and M2 reflectivity was measured before and after the realuminisation. The reflectivity of M1 and M2 followed very closely the expected aluminum reflectivity See a plot: http://www.not.iac.es/telescope/refl/ The improvement can also be seen from the ALFOSC zero point monitoring. Notably, the present zeropoints are 0.15, 0.09, 0.05, 0.03 and 0.00 better then from the 2009 realuminisation, for UBVRI respectively,

*I have been helping Carlos & Graham with the M2 work

ALUMINIZATION

Participated in the aluminization, very hard and interesting, was many years since last time. The finger tip feeling for certain crucial parts was still there. Unfortunately the topunit displacement motion did not function properly and there are still issues with unsmooth motion, replacement of motor/gearbox is discussed, the encoder for the positioning might also be worn.

Aluminisation -------

Produced the working schedule for the aluminisation including travel plans and assigning jobs to people.

-With PB prepare for M1 alum. ,tools location, planning, elevator mounting and test, etc..

-A lot effort on M1 and M2 aligns, several tries, meassures, repositions...But a nice thing is that a new tool has been desig and built for removing out M2 from the top unit in a safer, faster and easier way.

FIES general

- The adapter pick-off mirrors were cleaned during aluminisation: guider, STANCAM, FIES

Top unit ----

Following the aluminisation there is an on going issue with image quality. On the first night a significant offset of the images on the detector was found, initially this was corrected for by applying tilts, via the tilt mechanism, to the secondary mirror.

On the following day the M2 cell was adjusted to try and correct for the applied tilts. The following night the tilts were again adjusted and seemed reasonable, in range. Sometime during this work it was noted that the displacement mechanism was not working properly, not covering the full operating range.

The displacement mechanism was adjusted by lifting the M2 cell and seemed to be ok, can move in its full operating range. Numerous things have been done to get the 0.6mm motion back to its pre-aluminisation state. At present it still moves it full range though with some unexplained apparent jumps. Also it seems to sometime stop moving at lower altitudes when track "down".

Both the displacement motor and its gearbox and the displacement encoder have been suspected, but no conclusive evidence points to either been the culprit of the variable image quality.

Image quality is variable, with a long period after aluminisation where the telescope never got images better than 0.7 arcsec even though the DIMMs were frequently showing better than this.

On re-measuring the vertical height of the primary mirror wrt the mirror cell it was found that at two load-cells, values differed from the numbers written down from before the mirror was removed. Checks it was discovered that one load-cell connection was not installed correctly. after this was fixed it is now believed M1 is correctly positions, though due to this change an even large tilt of the secondary, actually putting it at its range limit, is required to get images close to the centre of the detectors.

The NOTCam high-resolution (HR) camera has been used to try and identify the image quality problem but with inconsistent results. It has shown ellipticity of 0.3 but at a positions angle of 30 degrees where you would expect zero if caused entirely by the displacement movement of the secondary mirror. Checking with the internal 50um (0.367 arcsec) pinhole, no image distortion can be seen, with the pinhole giving virtually perfect round images.