WHT optics log
In the log below, the data lines give numerical results from the
Shack-Hartmann tests, in arcsec, with the following format:
- Date
- Focal station (aux = Cassegrain auxiliary port)
- Telescope elevation
- Raw image rms
- Raw image 80% diameter
- Rms with low-order aberrations subtracted
- 80% diameter with low-order aberrations subtracted
- Speherical aberration rms
- Coma rms
- Coma extent
- Astigmatism rms
The analyses were performed using Dave King's newhart program.
FWHM = 2.3 * rms.
9108 Secondary reglued
Date Foc El Raw Raw Sub Sub Sph Coma Astig
rms 80% 80% rms rms rms ext rms
941117 Aux 88 .11 .38 .28 .08 .05 .05 .05
58 .10 .36 .27 .07 .02 .05 .04
30 .10 .37 .26 .07 .02 .06 .04
83 .10 .37 .26 .07 .02 .04 .06
(very similar to 12/93 results)
9508 proprtional controller for mirror support
951007 primary aluminised
951008 wrong spacer, no useful data
951120 secondary aluminised
Date Foc El Raw Raw Sub Sub Sph Coma Astig
rms 80% 80% rms rms rms ext rms
960318 Aux 88 .14 .51 .36 .10 .04 .05 .24 .07
57 .12 .47 .29 .08 .03 .07 .33 .06
30 .11 .41 .29 .08 .02 .06 .29 .04
83 .12 .43 .29 .08 .02 .07 .34 .05
961002 primary aluminised, subsequent o/focus images show coma extent
of approx 1"
961017 mirror support definers tweaked to reduce coma extent < 0.3",
as judged from o/focus images
961122 Aux 82 .12 .43 .32 .09 .01 .05 .26 .06
52 .12 .43 .32 .09 .04 .06 .30 .03
82 .12 .44 .32 .09 .04 .05 .25 .05
Cloudy, test terminated by bad weather.
Increase of tel AZ changes x,y of spot by -5.5, -3.5 /arcsec
EL -3.5 5.5
971113 primary aluminised, coma ~ 1 arcsec evident from o/focus images
Date Foc El Raw Raw Sub Sub Sph Coma Astig
rms 80% 80% rms rms rms ext rms
971113 Aux 86 .23 .85 .42 .13 .00 .18 .95 .07
50 .20 .70 .38 .11 .01 .16 .83 .03
29 .23 .79 .43 .13 .01 .18 .95 .02
971119 primary-mirror axial definers tweaked
971119 Aux 83 .11 .38 .29 .08 .03 .03 .19 .06
(following tests to check optical quality at PF not compromised
by 97119 tweaking)
Date Foc El Raw Raw Sub Sub Sph Coma Astig
rms 80% 80% rms rms rms ext rms
980414 PF 85 .13 .47 .40 .11 .02 .01 .06 .08
74 .26 .74 .65 .22 .02 .02 .13 .13
64 .16 .57 .43 .12 .02 .04 .18 .10
50 .14 .50 .48 .13 .00 .04 .22 .03
down to elev 17 (seeing too poor to use data),
now coming back up...
31 .15 .39 .34 .14 .01 .02 .10 .06
47 .14 .46 .46 .13 .01 .03 .21 .04
60 .13 .46 .33 .10 .04 .05 .23 .05
81 .24 .78 .64 .20 .02 .02 .13 .12
88 .22 .82 .62 .17 .01 .08 .40 .11
9809 Primary aluminised (gauges measuring axial position
of mirror replaced since 1997 aluminising, hence no coma
expected)
980910 Aux 78 .06 .31 .07
62 .05 .51 .05
33 .02 .30 .06
77 .01 .38 .12
990506 1-kg weight fell onto mirror. Chipped, but no change in CALIBRATE,
so mirror not moved.
990527 Cass TV images markedly astigamtic, slit has moved
990530 Aux 65 .10 .39 .25 .07 .03 .06 .29 .06
000613 Primary aluminised
000616 Aux 77 .11 .37 .28 .09 .01 .05 .26 .05
50 .15 .36 .32 .12 .06 .06 .29 .02
31 .14 .40 .34 .11 .06 .07 .37 .03
Date Foc El Raw Raw Sub Sub Sph Coma Astig
rms 80% 80% rms rms rms ext rms
001108 Aux 75 .14 .47 .34 .10 .01 .07 .46 .06
40 .12 .41 .32 .09 .00 .07 .42 .03
(suspected optical problem actually a feature of INGRID)
010923 Secondary mount driven to (focus) limit, collision with
a cable connector introduces large coma.
Elevation CALIBRATE coefficient has changed by ~ - 40 arcsec.
011029 Secondary remounted.
Elevation CALIBRATE coefficient back to normal.
Shack-H mounted at aux port but seeing bad, reduction
software unable to match spots reliably.
Date Foc El Raw Raw Sub Sub Sph Coma Astig
rms 80% 80% rms rms rms ext rms
020326 Aux 79 .22 .85 .36 .10 .03 .17 .83 .10
(vector plot similar to that of 011129, so this is probably
residual coma from the 010923 event)
020420 Tilting secondary from handset:
Transducer readings 1 2 3
Control-cabinet channels 7 8 9
Correspond to pivot Q motor P motor
Pivot is in elevation direction.
Q-, P+ on handset increases transducer readings 2,3
assumed to indicate movement in elevation.
Q and P speeds are 4.0 and 2.1 microns/sec.
TCS displays of transducers out of range at +-100,
so used LCD displays of LVDTs instead.
Date Foc El Raw Raw Sub Sub Sph Coma Astig Coma
rms 80% 80% rms rms rms ext rms PA
020420 At start of night, star image slightly comatic on ShackH TV view.
020420 Aux 81 .17 .59 .34 .10 .05 .12 .81 .02 -6
36 .20 .69 .35 .11 .08 .13 .83 .05 -14
Move secondary transducers P and Q 50 microns and back.
67 .08 .12 .76 .06 -11
Secondary LVDTs now read -38 85 69 on LCD display.
Tilt secondary in elev to -74 135 119 i.e. 50 microns each on Q and P
81 .07 .12 .81 .03 -6
Tilt secondary in elev to -101 185 169 on LCDs i.e. another 50 microns.
77 .10 .10 .67 .03 -6
Tilt secondary in elev to -154 285 269 on LCDs i.e. another 100 microns.
70 .09 .06 .34 .06 47
Tilt secondary in elev to -199 285 469 on LCDs i.e. another 200 microns
on Q.
59 .07 .04 .22 .05 133
59 .06 .03 .18 .06 159
79 .06 .06 .37 .08 -172
79 .06 .07 .38 .10 161
35 .07 .10 .59 .13 140
35 .08 .05 .25 .09 118
82 .18 .62 .47 .14 .02 .04 .23 .10 138
NB PA of coma (from sharp to blunt end) on CCD is measured clockwise
from vertical. Stars move at PA -45 when elevation increased, PA -135 when
azimuth increased.
During reduction, inner and outer spots masked out but vanes invisible
(up-down, left-right) so not masked.
No evidence after tweaking for distortions of in-focus or out-of-focus
images on ShackH TV.
Net movement was +200 microns on P, +400 on Q, i.e. a tilt ~ 80 arcsec
(+- 20%).
A tilt of this magnitude should cause coma 0.6 arcsec, which is
consistent. NB we might have simply compensated for translation by
introducing tilt, which would degrade image quality off-axis,
but this will be < 0.2 arcsec at 2' radius (e.g. INGRID).
020420 UES CALIBRATE coeffs AZ EL HC have changed from -21 -140 70
to -25 -90 130. A change of 50 arcsec in the EL term
corresponds to secondary tilt 110 arcsec, broadly consistent.
Date Foc El Raw Raw Sub Sub Sph Coma Astig Coma
rms 80% 80% rms rms rms ext rms PA
020425 Aux 66 .09 .32 .28 .08 .01 .05 .24 .02 123
Checking no change after top-end flipped.
021218 Primary mirror replaced after first aluminising for 2.5 years
021218 Aux 79 .15 .49 .38 .13 .00 .06 .31 .05 79
Aux 45 .14 .47 .41 .13 .00 .05 .25 .02 135
030409 o/focus image pair taken at aux port by AZ, no aberrations
0411** secondary aluminised
041123 pointing ~ 1' out in elevation, focus at LIRIS, aux and GRACE
prob increased by 0.3 mm
o/focus image taken on LIRIS, aberrations < 0.5"
Shack-Hartmann OK:
Date Foc El Raw Raw Sub Sub Sph Coma Astig Coma
rms 80% 80% rms rms rms ext rms PA
041123 Aux 84 .12 .42 .28 .09 .05 .03 .18 .06 137
The support of the secondary mirror was apparently too rigid,
due to a misplaced washer on one of the springs. This could
affect pointing due to flexure of the mirror backplane being
picked up by the LVDT transducers and fed back to the TCS,
without affecting optical alignment.
Support adjusted.
Date Foc El Raw Raw Sub Sub Sph Coma Astig Coma
rms 80% 80% rms rms rms ext rms PA
041124 Aux 86 .12 .41 .35 .10 .05 .02 .13 .06 73
041124 Aux 57 .14 .46 .35 .12 .03 .05 .27 .04 116
041202 Primary aluminised
041211 Aux 76 .08 .28 .26 .07 .03 .01 .09 .02 -159
070131 Primary aluminised
Date Foc El Raw Raw Sub Sub Sph Coma Astig Coma
rms 80% 80% rms rms rms ext rms PA
070202 Aux 75 .13 .48 .36 .10 .05 .04 .21 .05 -88
70 .15 .53 .38 .11 .03 .07 .36 .07 -74
46 .14 .52 .47 .13 .04 .05 .24 .03 -137
33 .10 .38 .25 .08 .03 .03 .18 .05 174
070405 Test of optical quality at the previously-unused broken-Cass focus,
in anticipation of the possible deployment there of the HARPS-N
fibre feed.
Out-of-focus white-light images were obtained (the Shack-Hartmann
camera could not be mounted) at telescope focus 92.0 and 104.0 mm (best
focus +- 5 mm), elevation 70 deg. Results:
COMA: < 0.3 arcsec (FWHM)
SPH. ABERRATION: < 0.2 arcsec (diameter of disc of least confusion)
ASTIGMATISM: < 0.3 arcsec (diameter at best mean focus)
These limits are consistent with the values measured using the
Shack-Hartmann camera at the Cass auxiliary port 2 months earlier
(070202 above), each aberration ~ 0.1 arcsec FWHM.
On an image of the globular cluster M3, the images are round,
with FWHM 1.3 arcsec, and no apparent changes in form across
the 60-arcsec field of the camera (0.06 arcsec/pixel).
An image taken at elevation 20 deg showed the (expected) ~ 2-arcsec
dispersion in the elevation direction, but otherwise nothing
unusual.
091103 Primary aluminised (no subsequent Shack-Hartmann, because of bad weather)
120208 Primary aluminised
Date Foc El Raw Raw Sub Sub Sph Coma Astig Coma
rms 80% 80% rms rms rms ext rms PA
120209 Aux 82 .13 .43 .33 .09 .03 .01 .04 .08 -151
34 .12 .45 .34 .09 .01 .02 .10 .08 156
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