This page contains 'typical' images along with some examples of 'odd' images with a brief explanation of what is causing the problem and some advice on how to fix it.

Pupil Images

Pupil images, and hence the lbcfpia code, may be affected by the internal factors which can be controlled: conditions of the mirror (is there a temperature gradient; are all actuators functioning) as well as external ones: seeing. If seeing is greater than 1", it is probably not useful to spend too much time trying to focus and collimate with lbcfpia, and instead to simply use the collimation lookup table (ask the telescope operator to 'revert to collimation lookup table'). The following images show 'typical' pupil images for which lbcfpia converged (zernike coefficients less than ~200 nm) in 1-2 iterations and those for which it did not and manual intervention was needed. |

Pupil images on which* lbcfpia *works
typ_s30.jpg collimated Pupil image when well-collimated. Rotator angle = 6 degrees. Note the small scale variations in illumination which are a sign of good seeing, but the overall large-scale uniformity, a sign that the system is reasonably well-collimated. This was taken before starting a 10-pt dither sequence, the first image of which had stars with ~0.7" FWHM. Obtained 12-Dec-06 UT**
typ_s33.jpg collimated Another pupil image when well-collimated. This was taken at the end of the 10-pt dither, ~20min after the image above and at the same RA/DEC. The last image of the dither sequence had stars of ~0.75" FWHM at B. Rotator angle = 17 degrees. Obtained 12-Dec-06 UT**
lbcb.20061121.034505.jpg excellent seeing This pupil image was taken on 21-Nov-06 UT in 0.5 arcsec seeing. Note the uniformity of the pupil and the crispness of the swing arm shadow. Rotator angle = -193 degrees. There is a bit of residual thermal gradient leaving the image with slightly too much positive spherical aberration.
Pupil images for which manual intervention is needed
ringout.jpg Radial Temperature Gradient The mirror temperature was warmer than ambient which caused a radial temperature gradient over the primary after opening up. This manifests itself as a bright ring around the outer and inner perimeters of the pupil, similar to a higher order spherical aberration which lbcfpia does not correct. Manual intervention is needed. Ask the operator to add ~1000 nm of Z11 (spherical) and try lbcfpia on the pupil image taken after that. Obtained 04-Oct-06. Rotator angle = -245 deg
ringin.jpg Radial Temperature Gradient Another manifestation of the radial temperature gradient. In these pupils the bright ring around the outer perimeter of the pupil is gone, there is no discernable central hole, and instead there is a steep fall-off in the illumination with increasing distance from the center. Obtained 04-Oct-06. Rotator angle = 13 deg
t2_1212.jpg Radial Temperature Gradient This pupil image from 12-Dec-06 shows again the strong fall-off in illumination from the center to outer perimeter of the pupil. On this night, the dome had been shut for several days and the mirror was 10 deg C above the ambient temperature, the limit of operation. The inner ring is more visible than in the previous example. Adding ~500-1000 nm of Z11 brought the pupil into the regime where lbcfpia could converge
tempuneven.jpg Uneven temperature distribution across primary mirror This blobby pupil image was obtained on a night when mirror ventilation was not working well. Later it was discovered that a hose had been disconnected and the air was not distributed through the mirror cell. If you see an blobby pupil image, ask the telescope operator to plot the faceplate temperature distribution.
** The shutter was stuck open this night, but these pupils are bright enough that the readout trails do not significantly affect the pupil illumination and structure and the images are fine for illustrative purposes. Coma and poor seeing lbcb.20061223.071044.fits:
coma1.jpg Coma & poor seeing This pupil image was obtained at the start of a night when these was some difference between the ambient temperature (-7.5C) and mirror (-5C). The bright crescent near the bottom is indicative of coma and was corrected manually using the chart ByEyeAOa.pdf in ByEyeAO. The pupil image is so blurry, because of poor seeing, that the spider doesn't show up and the rotator angle was read from the header. The bright crescent is on the same side as the spider opening angle, which according to the cartoon, indicates that negative Z7 should be added. Z7 = -1000 nm was given.
coma2.jpg Less coma & poor seeing This pupil image was taken immediately after giving Z7 = -1000 nm. It still shows coma, but lbcfpia was able to take over and after 2-3 more iterations converge.
coma20070108_014724.jpg Coma at beginning of night A comatic pupil image from the beginning of the night on 8-Jan-2007.

Other pupil images
norot.jpg Pupil image with no rotator A 32 second pupil image taken near zenith with rotator disabled. It is easy to overlook the fact that the Telescope box in the OB execution page should be checked to enable rotator tracking, as well as the telescope functions (slewing and telescope open-loop tracking). The pupil image uses a subset of rows on chip 2 near the rotator center. Note the pupil shapes show rotational trailing.

Science Images

lightdagger.jpg Light Dagger Scattered light pattern, position on focal plane array changes with rotator angle which suggests a fixed source, perhaps outside the instrument Latest news from F. Pedichini is that the fiber optics connectors to the controller emit near-IR (850nm) light. Fibers were rerouted in January 2007 to suppress the stray light.


uflat.jpg U flat The pattern is from the CCD manufacture and is removed in flat fielding. It shows up more in U than in B or V. The rings on the left center and bottom right are out of focus stars. There is vignetting around the edges for all filters.


shutterstuck.jpg Shutter Stuck Open The image shows trails in the positive y direction caused by the shutter remaining open during readout. The problem first occurred in December 2006, and was cured in January 2007 by replacing a damaged ball bearing in the shutter drive.


015312.jpg Horizontal banding on Red Array These images are not infrequent - we think they are limited to low background images. The amplitude peak-to-valley of the banding is about 10-15 ADU (see plot of row vs sum of counts across ~2000 columns) and is about 10% of the background. Redbanding.jpg
-- OlgaKuhn - 19 Dec 2006; JohnHill - 02 Feb 2007

  • lbcb.20061121.034505.jpg:

I Attachment Action Size Date Who Comment
015312.jpgjpg 015312.jpg manage 124 K 18 Jan 2008 - 23:22 OlgaKuhn Image with LBC-Red which shows horizontal banding
Redbanding.jpgjpg Redbanding.jpg manage 46 K 18 Jan 2008 - 23:21 OlgaKuhn Banding amplitude ~10-15 ADU. This plot is the sum over columns of chip 2.
lbcb.20061121.034505.jpgjpg lbcb.20061121.034505.jpg manage 174 K 25 Jan 2007 - 04:54 JohnHill lbcb.20061121.034505.jpg
tempuneven.jpgjpg tempuneven.jpg manage 10 K 18 Jan 2008 - 22:32 OlgaKuhn uneven temperature distribution over faceplate
Topic revision: r13 - 21 Jul 2009, NormCushing
This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding Foswiki? Send feedback