LUT Alt-Az images

Comparison of Alt-Az Scans

Here we compare the scans taken Oct 2, Nov 20, Jan 26, March 25
Note that this plot has "measurements" not "corrections".


Comparison of Alt-Az Scan November 20 vs. Oct 2

Here are comparison plots of the Nov20 scan vs. the Oct 2 one. I would characterize the angles as agreeing quite well, and the decenters agreeing very well in shape, with offsets of up to 1.0 or even 1.5mm in some regions of Azimuth. This size change in the decenter is consistent with the variations in decenter, compared to the LUT, seen over the last 10 days of observations. From this I would conclude that 1mm size variations will continue to occur in decenter, and that if we wish to do better we will have to use the active system.

Note that for dz I show the raw comparison, and then also one with the dz from the Nov. 20 scan corrected by a factor Delta UpperTrussTemp * 110.microns. IIRC the Oct scan had quite stable temperature, whereas the Nov scan varies in temperature by 1.5 degrees. The comparison is certainly improved with the temperature correction.

Alt-Az Scan November 20

Here are plots of the 5 hexapod degrees of freedom from the donut measurements for the Alt-Az scan taken on November 20.

Note for cognoscenti: these plots are of the "measured value" not the "correction".

Comparing these plots to the previous ones taken Oct 2nd, there looks to be rather good agreement in dx, xt, and yt. However, dy appears offset or scaled from the previous images, but with the very much the same overall shape. And dz now looks somewhat random compared to the very systematic variation seen before. This latter could be due to the change in pattern - this scan was done by going down in Alt, over in Az, up in Alt, repeat, whereas the previous scan was down in Alt, around 2pi in Az, then down in Alt.

Alt-Az Scan October 2

Here are the plots from the donut analysis from the Alt-Az scan on October 2nd.