The JCMT telescope is a 15 meter submm telescope located at the summit of Mauna Kea, Hawai`i. The surface of the main dish consists of 276 panels, each of which can be moved by means of 3 motorized adjusters. The panels were fabricated at RAL and consist of honeycomb structures with thin aluminum surface panels glued on top. Typical rms values for surface roughness and systematic deformations of a panel were estimated (in 1996) to be 12 and 13 micron, respectively. The dish is regularly adjusted for seasonal thermal effects using holography. The rms of the residual surface errors after an adjustment is made is typically 24 microns, as measured by holography using the new RxH3 receiver. This number does include the imperfections in the individual panels, in contrast to results from RxH2 before 2002.

Some older information about the surface until the first adjustments with RxH3 is given here.

In November 2002 the new panel analyses software was first used to derive moves files from RxH3 maps to adjust the surface. Since then we the rms at nighttime was improved from about 35 micron to about 24 micron. On 18 December this improvement was confirmed by comparing SCUBA FCF values with the 'old' and 'new' surface at 450 and 850 micron. Currenly we use 160 GHz maps to derive moves files since they proved to be more accurate (rms about 5 micron lower) than 80 GHz maps (which take less time to obtain).
In March 2003 we tried to move 30 motors with certain error status, and they appear indeed to move. This caused improvement of an additional few micron in the rms. There remained 35 adjusters which cannot be moved. However there are systematic deviations in the derived moves that are probably time (temperature) dependent - see e.g. here. This will be investigated as more maps are being obtained.
In Autumn 2003 improvements were made in the adjuster electronics which resulted in a repair of the lines of faulty adjusters in sectors 2 and 7, some of which had large deviations. The panels with these adjusters could be moved. However there are now two new series of adjusters (in sectors 4 and 12) which have phase errors, but these panels have only small deviations. At the moment (September 2004), 28 motors cannot be moved, 4 of which have large errors (>60 micron) and 5 have medium large errors (30-60 micron).

• Short instructions for RxH3 maps.
  
• Log of RxH3 observations and adjustment (tests).
  
• Adjuster motors and their status ; Priority list for repairs (9 September 2004).
  
• Changes in the surface observed in the period June - November 2004.
  
• Changes in the surface observed on 24 April 2004 and comparison with the measured temperatures of the dish.
  
• Calibration tests in different weather conditions. June 2003
  
• Correction of 28 motors with wheel errors and wheel reference. March 2003
  
• Adjuster tests made in May - August 2002
  
• Surface changes seen on 15 June 2002
  
• Standing Waves seen in 80 and 160 GHz maps.
  
• A drawing of the wiring connecting the adjusters in a sector of the dish.

The surface of other telescopes:
HHT
SMA
GBT
KOSMA: holography photogrammetry
LMT
IRAM 30m
Effelsberg
ALMA, also here or here